- Diode Test Range In Digital MultimeterPosted 380 days ago
Electronic Repair Questions/Answers and Testimonials- Part 35
Hi Jestine !
Hope you are fine. Thanks for the “master’s hand” in this wonderful and easy to understand piece of work. The newest person in this field will feel confident after reading just a few pages of your work. More greese to your elbows!
Hi Mr Yestine
Yesterday for the first time we did repair a LCD TV MONITOR SAMSUNG
The device had this malfuction When the client wanted to turned it on , It became on and off unvoluntary so out of logic According to your lessons we soon realised the the problem was concetrated in power supplay SECTION Measuring we noticed that a CAPCITOR 10V 1000 MICROFARAD was not working properly
We replaced it and WWWWWWWWOOOOOOOOOOOOOWWWWWWWWWWWWWW
The plasma worked very good as being a brand new. So your books really helped us
For us is as you gave to us for free that books Thank you again and regards to your family
Your friends from albania
ADI & BLEDI
You are probably aware of the issue of defective inverter module transformers because these transformers are burning up or the windings are opening up internally so we need a foolproof method of testing the primary and secondary windings of these transformers.
For example, I now have two Westinghouse, LCD TVs,
This weekend another customer brought in a second Westinghouse TV to our shop with the same complaint. I then removed what I though was a good transformer from this TV and installed it on the first TV with a known bad transformer. When I installed the repaired PCB back in the first TV, and pressed the power button, the TV came on with a good picture and sound and stayed on. So, I then knew for certain the defective inverter transformer was the cause of the TV going out.
Next, I removed the repaired Inverter/Power Supply PCB from the 1st TV and installed it in the 2nd TV and it came on with a good picture and sound. So, I know it is again a defective inverter transformer issue. The original Inverter/Power Supply PCB/module is manufactured by Darfon and has a model # B070-401, as well as the part number 4H.B0700.051 /B1 printed on the PCB. The part number of the inverter transformer is 4301H746030 <GP> printed on the transformer.
So, Jestine, what I would like to have is a simple method using an ohmmeter to be able to check the windings of the inverter transformer. I am assuming these transformers have a primary winding, as well as a secondary winding, but have never seen a schematic diagram of an inverter transformer. So, it would be helpful to me and other Electronic Technicians to have a simple method of testing these transformers. Do you know of a simple method to test inverter transformers? And, if so will you send me a copy of your method of testing them?
As always, I appreciate your help and support in resolving this technical issue.
Thank you very much!!
Thanks for the email. To test the high voltage transformer, i would normally do two test. The first test is to test the secondary winding (output winding) with Blue Ring Tester to see if it had developed any short circuit or not and the second test is to check the ohm continuity of primary winding with ohmmeter. It should show very low ohm. You can also use ohm meter to test the secondary winding that will show higher ohm, may be several hundred ohm. However testing for the continuity at the secondary side is not accurate that’s why is use the Blue Ring Tester to check it.
I suggest that you visit http://www.eserviceinfo.com to download some free schematic of lcd tv or even lcd monitor to analyze the inverter board and see how the high voltage windings are connected. Hope this helps!
this article (Understanding The High Voltage And X-ray Protection Circuit In CRT Monitor) is very vital and useful for anyone that work in the field of repair .i got to much
benfit thank you so much
I want to thank you for the information given by you that has enabled me to repair my lcd successfully. I do not have any electronic background but I can find my way to schematics and understand some basic instructions and had make a few diy devices in the past.
This is the website I went to – http://www.electronicrepairguide.com/dell-e153fpc-lcd-monitor-repair.html
I must say your tutorial is most informative and the pictures is a plus for us half-blind-man. Sorry for the metaphor.
Keep up the good work.
Sir, can you help me how to test this component str f6656 sk2520. it looks like a transistor but it has four legs. it is hot so i want to test it but i dont know how.
The components is an IC and you need to power on the equipment to test it. Since it is hot then i suggest that you get a new one for replacement.
Good day,thank you very much for the info.Now I have a monitor problem When i turn on the power of monitorit it is ok, but when i connect the vga or touch the pin of the vga connector monior is shutdown.can you give me what section of the cause the monitor to shutdown.thank you and God blessed.
If it it orange color (the LED) then it could be a defective CPU IC. However you need to confirm first that the signal cable h-sync and v-sync signal cable is good (no loose connection internally). Missing one of the signal could cause display to shutdown.
Hi I’m a little confused with nte numbering system.
I have version 13 on my pc for exp. i type in c3940 it gives me
replacement nte293( what is manufacturer part no for this transistor then)
Is it possible to explain to me how it works to better understand the
replacement of semiconductors etc.
According to my databook C3940 or 2SC3940 spec is 30v,1 amp, 1 watt and 200 Mhz and the equivalent number are 2SC2236, 2SC3226, 2SD1207 and 2SD1331.
Just a short note to ask a question of you on LCD monitors,
I have about 4 monitors to repair, the first has power but no video , I have followed your notes on checking for power, I have 300 volts dc at the filter capacitor and at pin 6 on the ic I have only 10volts dc instead on 16volts. I have checked the data sheet and it states that pin 8 hv has 300 volts dc and it generates 16 volts at pin 6 .Do I assume that the IC is faulty?.
Before that did you get any output voltage at the secondary side of smps? Try remove the power IC and test the voltage again. May i know what is the part number of the power IC. By the way pin 8 should not have 300 vdc otherwise the IC may have problem.
Another monitor that I repaired went great for about 4 days then I lost the video , if I switch the monitor off for a few seconds and then on again it comes on for a second or two, I am still thinking about that one
You mean the display shutdown after one or two seconds? If yes then it could be a bad backlight or problem with the inverter board. May i know what colour of the power LED when it shutdown?
.Another monitor that I repaired replacing the two push pull transistor in the output stage shorted out very quickly upon startup leaving me very surprised.
Check for dry joints at the high voltage transformer and also the p-channel FET (if the monitor have this transistor). Check also for tuning capacitor located nearby high voltage transformer and the value should be around .15 uf to .22 uf.
Your manual is very good and I am learing a lot about testing the monitors quickly , thankyou.
I have a Toshiba Qosmio laptop. Recently, the LCD Screen has “kong out” on me. It only display a vertical bar / line (as attached JPEG file). I was wondering whether you can help me fix this problem as your book only mentioned trouble shooting LCD Monitor.
From the description it seems like the problem is in the LCD panel. I had came across quite a number of this type of problme in LCD Monitor.
I have a laptop that is working fine but not very often, i got this problem. everything white on the lcd screen changes to pink. I am thinking about the inverter. any ideas?
If there is a nice display and the screen slowly change to pink it might be from a bad backlight. If it have only white screen and no wording (can’t see windows icon and etc) then suspect a bad lcd panel.
Dear Mr Jestin Yong,
Goog Morning,I Have assymblyed your Zener tester,but I have problem as test zener 18 VDC not accurate than I test zener 5 VDC ,is mesuered by analog pointer 6 VDC,the zener part is very hot than Resisotr and IC too hot, What is the Diagram is true ? Or any part to add for the diagram because when I short the probe RED AND BLACK sprinkling.fire on pointer..here your diagram circuit
Thanks for your instruction and replay my email…
Sorry i can’t open that link. I had many members that had successfully built the zener diode tester and the diagram is correct. Perhaps yours may have some problem that you need to double check. Have a good day!
Hi Jestine –
Downloaded your book And it is great –I have repaired CRT TV’s for many years .your book has a lot to offer to any tech .I was able to e[air an 32 Polaroid LCD that was competely dead ---no pilot light --would not turn on with switch or remote .There was an zener diode in the power supply that shorted ---cliped it loose and WALLA --back in business .Thanks for your help with How to check a zener Diode -----thanks again
Wow! Congrat and keep up the good work!
hello, mr jestine, how are you. here in
Take out the IC and power On and see if the supply voltage is too high or not. Test it with analog meter which can read faster than digital meter. If it higher than normal i suggest that you check the smps area.
Hope you are doing well.
I want to know that what is the logic behind placing the red probe(positive) of our multimeter at the cathode end of the diode and black probe(negative) at the anode to make it forward biased. Where as normally while connecting the battery terminal to the diode in order to make it forword biased we have to connect the negative terminal to the cathode and positive terminal to the anode.
Good question. The answer is because some of our meter have a output of reversed polarity from the probes. You can test the output polarity of the analog probes with a digital multimeter and you will know what i mean.
hi !!! jest
l have go through all the ebook
l am new cos not very sure how to put good use to it
but will try my best ,so now hope you can help me with this
1 have got a shorting circuit pcb borad for cecullar phone
how to find out where cos the shorting if repalcing
certain smd component l have ald manage a little bit of that
but comes to shorting am at a loss ,normally how to check
what cos shorting and from where to start the checking
Start tracing following the circuit trace where you found it shorted. That means along the line if you see any components connected to it then you have to solder out the component and retest the board again until found the culprit. Check especially semiconductor and capacitor component. Tracing this short circuit using the x 1 ohm range of analog meter. If you have other question please do email me again.
I would like to have some information / guide for CRT monitor repairing.
would you please help me to explained whole of the CRT monitor
Is there any way to replace Flyback monitor with anothe flyback because it dificult to find the original fly back for the monitor.
Sorry no. The best is still use back the same flyback. Have you try http://www.hrdiemen.com ?
I need another help from you. I managed to get hold of a Viewsonic VP171b LCD monitor, it has no display and no power light on the power led. I followed the e-book section of the "LCD Monitor Critical Voltage Test Points" to test the power supply, here is my finding :-
Bridge Rectifier :- 238VAC
Filter Capacitor Voltage :- 320VDC
Vcc(Pin 6) of Power IC 203D6 (I have attached the datasheet) :- 9.7VDC
Secondary Output Voltage Diode D5 :- 9.7VDC
Secondary Output Voltage Diode D6 :- 328VDC
Does it mean I need to change the Power IC 203D6, Diodes D5 and D6 since the reading is different from yours?
Thanks for the file and your test result. From the test result it can't be that the voltage of secondary diode D6 have 328vdc. This is too high. Did you put your black probe to cold ground when measuring the secondary diode? May i know what is the D6 filter capacitor value? I need this info in order to help you out fast.
Today I try to repair again this monitor, after few days ago got its FBT from
From last time all the local electronic repair shop never sell Monitor FBT. They only sells TV FBT.
I also found that the HOT shorted between C & E, then I changed with C5411 ( from BIC ) and it works! But after knocking the cover to check if there was still problem, the display became narrow in the middle, and I can't make it wider ( see the attached photo ). What is causing this kind of problem? How to solve it?
It was caused by a dry joint near flyback pin especially the modulation/damper diode package and if you did no solve this dry joint problem. It will cause the HOT to get burn again.
When you repair LCD monitors, how do you know whether the test point is logic 1 or 0, since they have several voltage level there, f.e.: 1.7V, 3.3V, 5V.
I don't troubleshoot LCD Monitor using logic probe because it did not have the TTL ICs. I'm only checking the voltage and the waveform signals.
Is there any logic probe in the market which could cover different voltage levels?
As fara s i know normally logic probe only covers logic low and logic high (max 5 volt)
refer to 2003 esr chart.
1- i can test caps that thier working voltages are not more than 250 v .
what about for exampel filter caps. in power section that their
working voltages are about400 or 450 how can i test these important caps. ?
Yes you can test cap of about 400 to 450 volt. You can make your own chart by testing on good 400 and 450 volt cap. From experience any cap that have low ESR regardless of the capacitance value is consider good.
2- what about caps that they are inbetween other voltages for example 47 microfarad but with 40 v not 25 and not 35
You can take the reading in between the two voltages for example if the chart value of 35 volt is 0.5 esr and 63 volt is 0.6 esr then you will know that 50 volt cap should have between 0.5 to 0.6 esr value.
is there any othr chart more comperhansive and in wider range?
Sorry at the moment i could not get any other good chart.
3- caps that their capacitance value are in between othres for example16 microfarad with25 v working voltage
i will be very thankful of your answers
Similarly with the above answer if you come across any ecap that have 16 uf then refer to the in between the chart for example 10 uf have 0.5esr and 22 uf have 0.9esr then the good value of 16 uf should be in betweenfrom 0.5 esr to 0. 9 esr.
For your information normally whenever a cap have problem the esr value will shoot up real high and you can easily spot them with ESR meter.
I read your news letter repair for the month of april and i thank you for all ideas that you shared to me.
You are welcome!
I just want to ask you about the trouble of one the monitor that i repair.The problem is the horizontal pincusion control can not adjust,but all contoll are functioning except for the horizonal pincusion.i can not adjust the horizontal size of this monitor.I follow your instruction on how to find the horizontal signal i put my anollog tester to the range of 10VDC,i select the osd on horizontal size and i press the + and - adjustment on the front pannel.while im pressing i put my positive prob to the pins of the ic one by one.and i cant find the signal the supply that varry up ang down.i have the same board of the AOC monitor in my shop i actually replace the eeprom and micro controller ic.but still does't change.Is this posible that the problem came in the flyback?I cannot actual it becouse the board here in my is missing the flyback.Is there any suggestion you help me to find the trouble of this monitor thank you for your help.
Okay you can try follow another method. Try tracing from the output of the horizontal yoke coils. Horizontal Yoke coil have input from the flyback high voltage (collector pin of HOT) and there must be an output. Follow this output line and test out all components especially the modulation diode and the pincushion transistor (usually attach to heat sink). If one of them shorted the display will have pincushion problem. Hope this helps!
I m from
This is a common fault and the problem is in the program of the MCU.
I have been reading on the repairs of the Samsung 153v but my one has
different syntoms when you switch it on it flashes the backlight goes
off. I have read your rightup on the 153v and cannot find the fault what
else could cause this problem.
thanking you kindly
It could be a bad backlight. Check all the e-caps and also the 4 pcs of 8 pins IC located behind the inverter board.
I am extremely impressed with your immediate reply and i must thank you for being great assistance to me. I bought this Hp entertainment pavilon laptop in late 2007
I handled my merchandise very carefully . Last week , i had no problem in downloading some music, transferring some music from my external disk and watching some movies.Last Friday, when i try to switch on my laptop, the whole screen was black and there was sound that the computer is on but nothing appears. It is not booting at all. I waited patiently like usual, but only to find nothing appearing at all.
I am at lost now, i can't do my work, neither can i check my mails or etc.
I sincerely hope ,you could assist me.
If the laptop can't boot this suggest that there might be problem in the mainboard. It could be Ram had loose contact, power supply failure or even bad motherboard. I suggest that you send to the laptop specialist to inspect the problem.
If the laptop can boot but could not see the display (it may be dim display) this suggest that either the inverter board have problem or bad backlight problem.
About the LG CRT Studioworks monitor problem, I didn't find any dry joint at the FBT area and had resoldered the damper diode and the safety capacitor, etc. But the display still can't become wider. Could you think any other possible cause of this? See the attached schematic around the HOT. The display can occasionally become normal but rarely happens.
If it can occasionally become normal then this suggest there is dry joint. Assuming there is no dry joint then you should check all components located along the collector line and also the Q761 area.
Getting the info about the safety capacitor from your blog yesterday, I do want to measure the capacitance of the safety cap to see whether it has dropped. Today I try to find the substitute from the junk mainboard of the LOGIX 17" monitor ( the pc tube already dim ), but unfortunately I can't find the 5600pF 1.6KV capacitor.
Then you have to find some value that is slightly higher then the original number.
When I searched for the safety cap from the junk board, I happened to see ( actually often sees this kind of mounting ) unusual mounting & soldering of a component ( marked as RV22 & RV29 on each of the pins ) near the big filter capacitor. See the attached photo. At first, I thought I can just pull it out, but it can't be pulled and finally got broken. Why the maker need to make this kind of mounting? What kind of component is that? Firstly I thought it was a varistor, but after checking with analog meter, it has resistance about 5 Ohms.
This is a thermistor and should show low reading. I do not know why the manufacturer wanted to put in that way-perhaps to secure it more effectively or to prevent from excess vibration that can easily break the outer layers.
Regarding the ATX power supply problem, the fuse is glass type and after the explosion still good. Actually when I repair many ATX power supply with blown MOSFET, resistor, optocoupler etc, I have never come across the fuse blown too. It is very strange or could it be the design of the circuit is bad? Instead, I found one of the varistor ( the board has 2 ) had short-circuited ( 44 Ohms ) marked as VDR2 on the board. Could the explosion sound come from this varistor?
If the fuse did not blow then yes i believe the sound came from this varistor. For your information not all power supply use varistor.
I overlooked this component when seeing at first glance because it was wrapped by black shrink tube. Since I don't have the part, could I power the ATX on without this part?
Yes you can but now the power supply have no more protection from surge
Do you think I could find this varistor in the local market?
Yes you can easily find one or you can salvage from another power supply
Could you help me make sure this component is a varistor?
Yes this is a varistor
Is the rating 150V? See the attached photo.
Yes the rating is 150 Volt that's why when you set to 230 volt, it immediately blow this varistor For a normal 240 V ac line designer will use a 270 vac varistor.
Last time you told me that your local stores don't sell monitor FBT anymore, so how do you get the FBT parts?
I refurbish on my own (for shorted cap). If i found shorted winding i will just return the set back to customer. I actually had bad experience about flyback from
May be after completing my fourth book i will write a book on how to completely refurbish a flyback.
i just received a 17 LG monitor model G774,the problem is when on around 10 mins the OSD automatically display out,can you guide me how to make trouble shooting,i seen your article like this before but i can not locate it anymore.
Make sure the eeprom IC get steady 5 volt supply and the
Can you please confirm the value of a resistor colour code brown, black, blue, yellow
Is this 10 Meg.ohms fouth band yellow 4% = 9.6 M ohms or 10.4
I have not work out this type of value for some time.
Yes you are right about the calculation but i'm doubt about tolerance. I have never come across such tolerance value before. Could it be 46 ohm with 1 percent tolerance if you read the other way round?
Also what is the best type solder to use on LCD circuit boards.
Use a 60/40 type of solder. (60 % tin and 40 % flux)
Where can i buy best quality soldering/ desoldering station
smd complete rework station, tired of surfing the net to no avail.
Try this website http://www.howardelectronics.com/
I will soon let you know when to send the link.
Both red wires voltage reading are 12.65V.
I guessed something is really faulty with the power supply?
Not really. You need to see if behind the red wires, s it connected together or not. I presume yes, it should be connected. This 12. 5 volt proof that the power supply is working. The 12.5 volt may go into another circuit that convert it into smaller voltages like 3.3v, 5 volt for use in the Mainboard. If there is voltages going to the mainboard and the power LED does not lit then this suggest that the mainboard indeed have problem.
could u please help me repairing samtron 4Bni model
it show short when connected in series light bulb every 3 seconds. If base of HOT is disconeected every thing seems to be OK but once base is connected it shows short. I checked x-ray circuit, B+ is ok diodes and IRF 630 are fine. I chkecked all the transistors they seems to be ok. where may be the fault, I'd be greatful for your precious help
It has a common fault of shorted internal capacitor. Please visit this link:
I have a Tv sony KV-BM14M40 with the problem of color, the violet color is dominated, it has RGB IC N0:- TDA61108AJF (TRIPLE VIDEO OUTPUT AMPLIFIER)
can u help me what to do
You can compare the signal and voltages of the color section in CRT board or even from the color IC. If the signal is not good from one of the output pin of the color ic then replace the ic and retest again. Before that you need to get the IC datasheet from the internet.
Thanks for reply. I understnd you. You are right. Problem is mcu (SE7889).
The SE7889 is not MCU. MCU is the other big IC with 44 pins.
Your Ebook is very resourcefull and informative. My LCD monitor developed a red and green line at either ends. What do you think is the cause?
Please if you have notes on how to repair CRT monitor, please send me. Currently, its CRTs that are common and needing lots of repair work.
I wish you the best.
If it developed lines across screen either horizontally or vertically then this is a fault of bad lcd panel and you need a new replacement. As for the CRT repair information please visit this link:
Have a good day!
Yes, you are the real master of computer monitor. Thank you for helping me repair this LG monitor and now this monitor works perfectly. I overlooked some dry joints because I didn't use any tools to observe the board, one is the Q761 and the other is Q753 ( KTD1413 ) which has the same heat sink as the HOT around the FBT.
Congrat on your successful repair-means more $$$$$!
Unfortunately I can't find the varistor in the local market for the ATX power supply. Do you think it is possible to replace it with ceramic or pelyester film capacitor? If it is possible, what is the spec of the capacitor?
If you could not find then don't install any components in it. Installing cap in this circuit would not help because it defeated the whole purpose of using the varistor. The cap is not meant for protection (surge).
I am determined to fix this one.
I sold the customer a new PSU, and kept this one to learn on it.
I replaced the AZ7500BP with a Fairchild KA7500.
I replaced the burnt resistor with a 100 Ohm, as you recommended below.
Now, when I switch on, the primary side works, but not the secondary.
Off the new 100Ohm resistor, connected to the KA7500 Pin12 (Vcc), I measure 15.5VDC - I think that's good. It doesn't burn!
But on every other pin on the KA7500, there is 0V!!!
On the LP7510, to the right of the 7500, also 0V on all 8 pins.
Almost all measurements on the secondary side show 0V.
It is as if the whole secondary side is locked down.
Now I saw something interesting, which I have not seen in another SMPS
There is this orange component labled THR2.
THR2 is maybe a thyristor, which can shut down a complete circuit. It is marked 500 642+.
On THR2, itself, is showing 73 Ohm resistance. I do not know of any otherway to test it, if it is a thyristor.
All the caps are OK ESR.
All diodes are checked OK.
The TL431, and 2SC945's are all checked OK.
Do you have any idea at all what can cause this complete lockdown?
No idea on that component but pc smps circuit is rather complicated. It required the first voltage to be present at the 7500 ic so that it can switch the two transistor and eventually sending signal to the switch the two transistors in the primary side. I suggest that you read this article at http://www.repairfaq.org/sam/smpsfaq.htm#smpsbdhtp
Saya sedang membaiki LCD Monitor Benq 17" M:Q7T4 masalahnye ialah Transistor FU9024N (Q805) rosak, saya dah tengok data sheet iaitu IRFU9024N, bolehkah saya dapati ia dipasar road dan apakah Equavalent bagi transistor ini, terima kasih
Parts ini biasanya saya dapati dari kawan saya tetapi dia telah berpindah ke
Hi Jestine I have a tv that wont turn on, there is no light
or sound just a humming noise, where do you suggest I should start. I
have never worked on this field but I want to learn so your
suggestions will be great thank you.
Check on the primary side of smps components first. A shorted HOT and secondary side diode could also give humming sound. The best is to separate the section by following this method at http://www.scribd.com/doc/2957819/TT204-Identifying-television-SMPS-problems
I can find three voltage regulator on the main board, U1 (1084 CE 492F6, TO-252), U2 (19 2D, SOT-89) and U3 (1084 CE 492F6, TO-252).
If I test the voltage regulator U1 and U3 based on generic 1084 as attached and using common ground, I get the following reading :-
U1 PIN 1 GND
U1 PIN 2 Vout - 2.57V
U1 PIN 3 Vin
U3 PIN 1 GND
U3 PIN 2 Vout - 3.4V
U3 PIN 3 Vin
If I test the voltage regulator U2 based on attached and using common ground, I get the following reading :-
U2 PIN 1 Vss
U2 PIN 2 Vin
U2 PIN 3 Vout - 5.16V
Both U1 and U3 have same part no. but readings are different, is this possible?
If u1 and u3 have exactly the same number then it should have the same output. Now the problem is it could be some leaky components (or shorted semiconductor) that can pull down the voltage. You can remove the pin 2 of u1 and u3 and retest again. if both have the same output and once connected to board and it drop then this means something had shorted that had pulled down the voltage.
The power supply went dead. I tested some of the coils with a flyback tester and it doesn't shows any LED light. I expected the coil is bad.
It depends on how big is the inductance of the coils. If the coils have higher inductance then your meter could test it. However if the coil is small and have less inductance your blue ring tester might only show one bar or no bar at all.
What places does customized coil that I could order from it?
I have no idea since many of the electronic shops do not sell customized coils. Not only coils even the smps transformer also they would not sell.
What would you do if you need to replace this type of coil?
I have to really sure that indeed the coil have problem otherwise i would be losing my time in repairing it. Assuming the coil is really bad then i will just send back to customer because those PC SMPS coil is not easy to rewind. I suggest that you take out from other smps coil and compare the reading for accuracy.
Is something I could winding this type of coil myself?
If the coil have single winding then you can try rewind it on your own. Just get back the same diameter and lenght of good coil and start to rewind it. If the coil have many windings in it then it will be more complicated and will easily take up your precious time.
You are welcome!
Thanks a lot and i have a quetion. that is Why SONY TV STR IS Damage quickly after replace new STR IC?
May be there is still other bad components that is corresponding to the IC. That means you have to check on other components first which include components in the secondary side before you replace the ic and turn on the power.
I am still trying to repair the lcd monitors that I have here, the one that I did have working for four days will still start up ok and the led remains green even when the screen goes black.The BENQ screen always comes up first followed by the computer screen but only for about 2-3 seconds, I have tested all the components that are visible to me and found them all ok, but I checked the voltage at the peco fuse and it was 27 volts which I think is too high and that's why the screen cuts out . I am not sure at the moment just where to look for that problem , I have been studying your ebook everyday and seem to come up with some new idea to try once I read your book each time.
Have you check the backlight? A bad backlight could cause the display to shutdown after 2 to 3 seconds. At least after shutdown the led still have green light other wise the mainboard may at fault. Check the high voltage transformer area too for dry joints. Compare the resistance especially the semiconductor between the top and the bottom lamp circuit. Any difference in resistance is a clue for you to locate bad components.
One of the other board which didn't have any video I found the peco fuse to be faulty but I have not tried it again since finding the fault.
If possible check the semiconductor components first before you install a new fuse. The fuse can break by itself or cause by shorted components downstream along the fuse line (supply voltage line). Have a goodd day!
How are you doing, hope ok,
Yes i'm fine thank you.
I`m enjoy receiving you newsletters, and learned a lot, as I’m a pc tech and have my own small repair shop, but I’m not a electronic guy, but as mention I learned a lot with your NWS letters and e-books,
You are welcome!
How can you test a inverter board of a lptop.
We have a lptop for repair
1 dim image on screen
2 video ok on external mon
3change lcd panel for known working one same problem.
All lead to a faulty inverter board.
But how can you confirm this by a test.
I did the following.
From the mother board to the INV board I got on pin 1, 19Vdc before and after the f1 fuse (fuse f1 is ok),so I assume that the MB is sending voltage to the inverter board?
The voltage is coming from power supply and not mb.
But what about the oter pins ?
Other pin is to trigger the circuit in inverter so that the 19 volt can be apply to the inverter IC.
Also found on the web that using a voltage meter with Khz reading (50khz or more) you can conclude if inv board is working or not.
Yes if the meter could pick up the signal this generally proof that the high voltage transformer is working fine.
hi bos good to see u r letter again, thanks very much. i know my skill in tube monitor not much but this is very amazing to me.
What is the price of the E Book and is there any bonus with the purchase of the book.
It is USD47.77 and yes the ebook comes with the bonuses.
Dose the book have fault remedies as I have a Diamond View LCD Monitor which is blinking all the time and the signal is only visual for 20 milli seconds.
It does not cover your lcd monitor model because in the market have just too many brands and models.
The reason i did not mention the specific brand was because i want all my readers to grasp hold of how i solve the problem so that he or she can apply the method to solve any other brand of LCD Monitor. There is a saying “If i give a fish to you, you eat for a day. If i teach you how to fish you will eat for life!” This is the same concept apply to LCD Monitor repair. I can’t write a book of power problem for brand “A”, brand “B”, brand “C” and etc because in the market there are few thousands of brands of LCD Monitors. Then another subject of display shutdown for brand “A”, brand “B”, brand “C” and etc. I always believe this word “Once you know the principles you will know the rest”.
Dose the book also show what voltages should be expected at testing points.
Yes it does show the voltages and waveform (but nor for your model). It is more as a guideline.
Do you give on line help and for what length period.
Yes u can email me if you have any lcd monitor repair question as long as you have question.
If you have other question please do email em again. Have a good day!
I am looking for something reliable. I saw some on ebay. What is the meaning of 10khz, 100khz and 200khz on the LCR meter????
This is a frequency used to test on cap for accuracy. You can read more by visiting this link:
The other meter I am looking for is the Insulation tester. I don’t know is the Kyoritsu brand reliable? a link on Ebay.
Yes this is a good meter and you can go ahead to get one.
Want to know if resistor get 0 ohms, open or short circuit ?
Normally resistor become 0 ohm (open circuit) or turn into high ohm that you need to test it with digital ohmmeter. so far i have not come across resistor that can get short circuit.
Hi Jestine, can you please tell me if you get a B+ of 90V
and B+ must be 97.5V, does it mean that your B+ is to low
to get the horizontal deflection started. In other words
must B+ be exactly 97.5V or can it be a little more or
less? Thank you
No not really have to be exact. That voltage was good to start up the flyback transformer . You also must make sure the Base of HOT is receiving a waveform from horizontal oscillator ic.
Thank you very much your quick response agin. I have a problem with computor ATX Power supply(Mercurry 450W). But Iam unable to find the fault yet. Plese can you help me for that. Problem is when swith on and short the PS-ON pin , Quickly turning the powersupply fan and within about 1 second it stop.It has a control ic call KA4515406303H and Iam unable to find the data sheet of this IC. Can you think about this problem and What is this ic? Please help me
It could be cause by bad filter cap at secondary side, bad IC, or even faulty components in the primary side. I suggest that you check for bad filter cap first with ESR meter then only move on to the primary side. If all tested to be good then only replace the ic. Unfortunately i do not have the ic datasheet.
i have got a samsung 153A lcd for repair. the problem is when we switch on the display comes and the light goes off but the display is there in the background.
is it the invertor problem or the lcd lamps.
It could be bad backlight or inverter board problem. Check all the e-caps in the inverter board and also check on the pico fuse too. If one of the smll 8 pins IC located behind the inverter board shorted also may cause the display to shutdown.
Thankyou Jestine for this wonderful newsletter on the Troubleshooting and Repairing of Mainboard. This gives me an insight to repairing mainboard with multipins ics. I often end my work on the mainboard if I suspect the ics are the problem. Often I look for replacement mainboards or cards only. But what you wrote now shed a new light into my work.
Thankyou very much once again Jestine.
Have a safe evening
Hi young, lam a regular reader of your fine electronics articles. i really enjoy them very
much. thank you very much for the effort you a putting in especially for some of us who want to be competent electronics technicians.
Hallo Mr. Jestine,
Thanks for the microcontroller news letter.
I have a Dell 17″ LCD monitor (model:E178FPb). the problem with it is that it changes colors (ie blinking red, green, blue etc)n which makes it un comfortable to the eye.
I have tried to open and check it but could not detect the problem
I would be grateful if you can help guide me into fixing this problem
Is the cable internal wires good? If it is good then suspect mainboard problem.
I´m a peruvian electronic technician but much time I´ve worked for telephone companies so newly I´m begining to do tv´s repairs. I have a problem because mostly of my clients ask me to work in their house, it´s to say they don´t want to move their tvs. Are there some tips for these kind of service ? Please I´ll wait your answer. Thanks
It is so inconvenience to work in customer house because you have to bring along test equipment and even parts with you. I can’t give any advice on this because i’ve never been to house and repair customer equipment.
How would you test varactor that might have been damaged to some degree by a near lightening strike? It seems to operate OK, but under a load, it heats up more then usual and if the load peaks, it seems to be erratic.
I suppose you are referring to Varistor and not Varactor. May i know at where you found this component? If it is a varistor then use an analog meter set to X 10 Kohm and it should have no readings in either way. If you found it to be erractic then direct replacement is the best solution.
Thank you for your info about Shenzhen elecronic market,
Is the content in coming your fifth book about refurbishing FBT also applicable to TV FBTs?
Only for CRT Monitor
In general, what are the requirements that an FBT could be refurbished, besides the primary winding is still good?
A shorted cap inside the flyback which contributed about 80% of flyback problem.
Before I look for the FBT in the local store, I did try buying junk ATX power supply from a computer store, but since I am his frequent buyer, he just gave it to me. After coming home and looking it inside, there is no varistor.
Some design use Varistor and some design do not have any.
The reason I insist on repairing this ATX is because I’m using this power supply to power my old HP Vectra desktop computer and it seems that this ATX ( Astec brand ) has its own proprietary design pinout of those 20 pins connector, the colors of the cable used for each pin are different from the common one. Now, this ATX is working well without one varistor as recommended by you. Thanks for your guidance.
Now, I am working on old Aiwa Integrated Amplifier. The problem is the protector relay for the speaker cannot tick ( losing 24V DC somewhere ). I have replaced the Speaker Protector IC but to no avail, then I replaced some resistor & capacitor in this relay & IC circuit. In fact those resistors and capacitors checked OK with meter but seems slower to the meter reading response. I have been working on this for a week, so instead of replacing those suspicious components one by one, I replaced them altogether. Because if replacing one by one, it would take longer time as I have to resolder some cables every time I need to test this set. Now, I did solve the problem, but I don’t know where is the real culprit. Do you always replacing suspicious components one by one?
Yes if i wanted to in order to find out the real culprit
Another interesting point is that there is a color-coded capacitor on the mainboard which first I thought it was a resistor. Do you ever see this kind of component when repairing monitors?
No, these kind of color coded resistor mainly used in older type of equipnment.
See the attached .doc. Also, there are some switches on the board, some of them are the function selector. If I want to clean the switch contacts, which cleaner should I use. When you would use the degreaser cleaner? See the photos of two kinds of cleaner.
Use the oil based cleaner 390SS.
Now I am about to repair a Philips CRT 105 S monitor, with the problem of no display, only with faint motor-like sound when turned on. Do you know what is the problem? If I find the BU4522AF HOT to be bad, can I also replace it with C5411?
No i have not come across such problem with this Monitor. As usual once you heard those sound, start checking from the HOT and isolate it to see if the problem is in SMPS or in the high voltage section. As for the replacement you can try that and then touch it with your hand. If it turned Hot within a second or minute then it can’t be use as replacement. You may have to use back the original number.
Last question is about the inverter tester in your newsletter, where did you buy it and how much.
I haven’t buy it because i’m not into LAPTOP REPAIR. The newsletter is more to educate technician how important to have good tester to help out in electronic repair work. You can try visit http://www.lcdparts.net and the selling price is USD119.90
hello sir how r u.sir i have a HCL HCM580 15″ CRT Monitor. what’s the complaint is when ever monitor switched on display comes and then monitor shutsdown immediately. i checked the B+ voltage which comes to FBT When we switch on the monitor there is 130-160 Volts and then suddenly it drops to 88Volts and it remains until we switch off the monitor.i cut the jumper between B+ line and FBT and in the place of jumper i installed a 60W Bulb in Series then the display is ok and voltage is about 120v-130v.i replaced all ecaps in Powersupply in both primary and secondry side but complaint is same. please help me to solve this problem.thanking you sir.
Try use the method in the link http://www.scribd.com/doc/2957819/TT204-Identifying-television-SMPS-problems
to isolate the problem. Check also for capacitance value change in the safety capacitor. If possible try remove the B+ fet and On to see if it shutdown or not. If no more shutdown then suspect the h/v oscillator sending a wrong waveform. Hope this helps!
Many thanks for your reply and guidance.
I’m still not able to fix this monitor. Here is what I have done:
Measured collector voltage of HOT and its steady at 88.5v for Windows and 49.4v for DOS.
Cathode voltage of of the diode feeding the xray protection circuit – Initial voltage is 63.7v and rises to 65v when it shutdown.
Gate voltage of P channel buck MOSFET – Initial value 182.7v and 186.8v when it shutdown.
Replaced the safety capacitor – tried again and same problem.
Replaced the TDA4851PS with TDA4856. I don’t have the TDA4851PS but I checked datasheet and specs and pinouts are the same. Tried again and same problem.
You have to use back the same part number. I came across this datasheet before where everything was same but just don’t work.
Next I removed the diode from the flyback that is fed to x-ray protection input pin 2 of TDA4841PS through some voltage divider. Tried again and still shutdown when HV is 25.2kv and become just 8kv. So I think it is not the xray protection circuit tha’t causing the shutdown. Jestine, do you think the internal capacitor on the flyback is the culprit ? If the internal capacitor value decreases as you apply the operating voltage will it cause the HV to rise ?
Yes it is possible-have you see this article before? http://www.electronicrepairguide.com/testing-flyback-transformer.html
I sprayed with freeze spray surrounding components related to xray protection, TDA4841PS IC, HOT and even the flyback itself but made no difference. I don’t believe it is heat related as HV shutdown happened within 1 minute after turning ON the monitor from cold.
Yes i don’t believe that either.
And why there is 8kv when it shutdown. Isn’t should be zero ?
The 8 kvdc could be still the charge from the internal capacitor. Yes by right without B+ voltage and base signal of HOT it should be zero.
I like to replace the flyback but I don’t have replacement for it. To let you know, I just salvage parts from other scrap monitor and power supply. This is the only Phillips monitor I have and all the rest are HP branded. Actually this monitor is already scrap, I just want to know what is cause and solution to this problem and get more experience as well.
If you need to replace the flyback, you must get the excat one otherwise it may immediately blo the HOT and cause some other weird problem.
Saya dapati wire putus di hujong backlight….ia itu wire warna pink..macam mana cara nak atasi problem ni..
..board ni kesmua nya ada 4 connector ..di bahagian atas 2 dan d bawah 2….terletak selepas inverter iransformer…2 set of wire pink dgn puteh 1 connector dan blue dan hitam lagi 1 connector..skrg problem wire tak bleh sambong lagi …dan lagi pun saya tak pernah buka backlight nampak macam susah aje….tolong saya mcm mana nak bypass ni wire?…sebelum tu ada problem power board tapi saya baiki ikut cara article awak….e153fpc…capacitor problem..
terima kaseh Isa
Wayar putus kay bahagian backlight nampaknya ia sukar di join kembali kerana tiada ruang yg lebih untuk solder gun sambungkan wayar tersebut. Oleh kerana ia pun dah putus, saya cadangkan anda keluarkan backlight tersebut dan tengok sekiranya anda dapat mencari ruang untuk kamu solder join tersebut.
I’m still reading your e-book, is realy interesting, all your experientices in LCD repair but I’m having some problems finding the information about some IC’s I found in a monitor, you mention some thing about find Vcc pin, but in order to fin it I need the diagrams of the component in cuestion, and there is the problem i can’t find web sites who offer them, I’m following your instructions as well as I can, another thing I need to solve is found some electronic stores around here and buy the parts locally to avoid time comsumption, other thing is how can I determine which are the right parts you are mention in the description you detailed, if the monitor is a diferent model, I’m a little confuse about it, thanks a lot for your time and help.
how can I course a class with you trougth internet as the same as you teach to your students in your school ???
Assuming if you can’t get the datasheet from the internet, the only way is to trace from the smps output that leads to the inverter IC. Normally the voltage will be around 12 to 18 volts. As for the parts, give yourself sometimes first and after many repairs you will know what are the components that you should store. As for the course, i can’t provide online course because this type of practical course got to get them to come here to experience themselves. However if you have LCD Monitor repair problem just send an email to me and i’m glad to help you out.
Do u have LG Flatron ez T 711S monitor service manual ?
Sorry i do not have. have you try http://www.eservicinfo.com ?
My friend send to me that monitor is no power . Why the back cover of this monitor had to open ? It’s only have 2 screw on the bottom , no other screw . After removed the screw , the cover still can not open , do u have any idea ?
No idea because i have not come across such model before. Is the Monitor still no power and what have you check?
From Shenzhen , do u get any new idea or spare part which is hard to find in
There are plenty of shops selling different kinds of electronic components and since my time was limited we just scan around and didn’t really look for hard to find parts in
Your Name: Waleed
Message: greetings. I know you are busy but i need to ask you this question. is there an article you wrote about reading the numbers on the fly back transformers? there are so many numbers and I do not know which one is the actual number when ordering ones on line or from the store. for expample. here are some number on this tv flyback transformer.
In fact sometimes i also confuse about the part number. In your example in can be the BS7773 L102 or the 13420020. I suggest that you email to the owner and check from them.