- Diode Test Range In Digital MultimeterPosted 379 days ago
Electronic Repair Questions/Answers and Testimonials- Part 55
How you doing,i hope everything will be OK.
Jestine;i can’t explain how much i appriciate,honour and love you,you are such a great person.because every moths electronic repair tips you e-mail to us are very interesting and teaching and also on the way gives me a message of affection which you have love and honhour on me/us.
Jestine,tell oyu trully what i think alwways,it was good to work together in one workshop with jestine.specially when i read the interviews you made with Steve French,your questions are the main poins which happens and feels to every tech.
your questions affected me because of your deep interest you have on me/us.
THANKYOU VERYMUCH JESTINE!
Hello Jestine I would like to say again thank you for your being generous and for me you are really great because even I am seldom in responding your newsletter still you did not stop sending me. And for your information all of the electronic repair tips you had sent really helps me a lot and I know that I could really get a lot more from your ebook.
Thanks for the links, I downloaded and took a quick look in all. Many many things are described and illustrated and I must admit it\s very impressing - the work to build those books, the experience and the will to show to others – this is really noble.
You are really something. You are a happy man (family + professional success).
It/s a great honor for me to meet you and your work.
I will get back soon to you for the other ebooks.
I find your book extremely useful and I am so glad that I bought it.
hi jestine: ive read a lot of your ebooks extensively and they are fantastic i cant keep my eyes off of them because ive learned so much from them
I just want to tell you thanks for your Blog section. Even reading your answers to the ERG members helps me to learn more about electronics. It is very helpful.
Thank you for your mail, I downloaded your report and found it to be very
informative. With the information you provided I was able to isolate and
repair the faulty capacitors in the power section of my fathers 15 inch
Viewsonic VA521 monitor. He was going to throw it away but I stopped
him and said no there has to be a way to put life back into it. I love to
repair computers or components but lack the knowledge. At this stage
I am self taught and am looking at going to university next year to study
and gain the knowledge to carry out more complex repairs. I am yet to
obtain your ebook and I look forward to reading its contents.
Have a great day..
My suspision moved on to the two transformers. These transformers are on the line with the two big diodes on one side with the two big filters and the + side of the bridge rectifier on the other side. When I touched the primary and secondary winding pins onboard with the analog meter probe X1 time. It makes a beep sound proving continuity. So these transformers seem to be the culprit to make one of the diodes (closer to the TF) to have two readings and the bridge rectifier to have continuity reading every pin i touched.
Well it could be the primary and secondary winding have shorted. I guess you need to remove it from the board to test again.
Do you have any idea how or where to get the replacement for the transformer (PF08A-42-PFC).
Usually smps transformer can’t be get from the market because they are unique in windings unless you can find the distributor for the set.
The primary side has 2 pins and the secondary side has 3 pins. No way to repair it right?
You may send to any motor/transformer rewinding shop to rewind it.
And, will it be a problem to use a jumper instead of the Thyristor?
No problem using jumper to replace the thermistor (not thyristor). In the future if there is any surge, the main components may blow.
My other question is; suppose I got another working SMPS, is it good to measure the plus and negative signs of the bridge rectifier DC voltage?
Yes you can measure the DC voltage when power On to see if the section before the bridge is good or bad.
Hope you and your family are well.
They are fine thank you.
I am thinking of getting an oscilloscope of ebay..what would be the least mhz that i can use for repairing lcd monitors and tvs as at the moment it will be a second hand one for now and don’t want to make the mistake of getting to low a mhz?
Get at least a 100 mhz.
I have read a little bit about scopes and also your info on scopes in testing electronic components and SMPS ebooks that i have from you.. Are there any tips you could pass on while i am trying to find one..
Those tips I have already include in the ebooks like testing sine wave of crystal, output waveform of oscillator ic and etc.
Have you ever considered an ebook just on the oscilloscope with a few more tips on testing certain components on monitors and smps showing the waveforms one should see and a section on the best settings to use for certain components ( like you did in the above ebooks you wrote) as i am sure it would be a good seller . I for one would pay for that info in an ebook.
Thanks for your suggestion but at current moment i have another project on thus i will put on hold all other topics.
Like i say the tips on the scope in your ebooks is very good and i am wanting to learn more using a scope for testing certain ic’s.
Yes you should and need a scope for higher chances of success repair rate.
Also would like to thank you for the fast shipping on the blue ring tester i ordered from you,a very useful tool indeed.
You are welcome and thanks for the support!
The Interview with Steve French was great .I found many answers to my questions.The Interview is very effective and motivated me a lot.
Your News letters are always full of guidance .Please continue the good work you are currently at and also share good and bad experiences of other techs as well .
Thank you sir Jestine for your unselfish work in dessiminating useful solid info in
the field of electronics.i really appreciate knowing you and have your email.i see i will realy benefit from you in the future.Thanks again sir.
Hello Jestine..sekiranya nak check voltan antara 250 to 300VDC dekat G2 di CRT board boleh ke kita switch on monitor tanpa cover heatsink yang menutupi CRT board tersebut?Kebanyakan CRT board monitor ditutupi dengan cover heatsink ini tidak seperti TV.
Boleh no problem.
2.Boleh tak beri saya tips cara-cara untuk check voltan heater?
Meter set a dc voltage, probe hitam ke ground dan probe merah ke heater point.
3.Mengikut tips yang awak beri sekiranya bacaan di G2 250-300 VDC masalah no display mugkin disebabkan ceramic capasitor yang terdapat dekat line G2 di CRT board.
Sekiranya nilai G2 rendah, ia boleh disebabkan oleh ceramic capacitor (along the line), flyback screen voltage (Variable resistor) dah set ke terlalu rendah.
Soalan saya adakah value ceramic tersebut sama dengan semua monitor atau berlainan value.
Bergantung kepada model. Cari gantian yang mempunyai nilai yang sama capacitance dan voltan.
Oklah saya harap awak dapar memberikan jawapannya nanti yeer dan saya ucapkan ribuan terima kasih.
SORRY TO TROUBLE YOU WITH MY PROBLEM I HAVE A KROSS60MM
LCD TV/VGA MONITOR AND WHEN YOU SWITCH IT ON YOU CAN NOT SWITCH IT OFF ONCE IT IS ON
PULLED OUT POWER AND WHEN I PUT THE POWER BACK ON IT COMES ON AGAIN I HAVE NOT TOUCHED IT YET OR TRYED TO FIX IT
SO COULD YOU PLEASE TELL ME WHAT COULD BE WRONG
I suspect there is something that had gone wrong with either the MCU or the EEprom programs assuming if the front panel buttons are okay.
i am AWAIS AHMAD from
I read your e-book ”how to test electronic components” and i find its has much helpful knowledge for me, i read the book to find the method to check mosfet and, i find its a good and easy method to check the mosfet.
Thanks for the support!
but still i have some problems to check the mosfet. i am trying to repair APC 1500VA smart UPS, its overload LED show on without any load, some body who repair these types of UPS tells me that its a power mosfet problems. Number is “IRF3205″ So i desold all these power mosfets from the circuit and check with your method that you can describe in your e-book, So all mosfets IRF3205 are showing good health. but when i examan these mosfets one by one with a magnifing glass i find that in all these mosfets there are some symptoms such as very small hole, hair line fracture, black spot on the body that shows like heatup on these mosfet.
so i think mosfets are not working at 100% when thay are in the circuit. so becuse my UPS show overload without any load.
kindly help me to solve the problem to checking these mosfets or tell me its is possiable that multimeter shows good health of these mosfets but thay are not woking 100%.
I could only says that the Mosfet can breakdown when under load. Even if you have the best tester on earth and the problem is small hole and etc, it still can’t be tested out. I suggest that you directly replace such mosfet and retest the set again.
Have a good day!
Thank you for the update and articles. Great article.
You are welcome!
Sounds a little like myself except I later went to college and got a degree in electronics. My earlier work out of high school was in a TV station working as an engineer but without a degree. I learned by independent study and actual work towards what I needed to know in broadcasting. Now I work for a community college in the electronics department. I am currently working with one student doing repairs on 4 basic 0-200 volt DC power supplies. Our science department keeps blowing them out. Each has some problems in various circuits and once they get fixed I’m going to watch what they are doing with them and find why they keep blowing them out. I need to put in some protection circuits such as adding a light bulb to the positive output which would light up if they were drawing too much current to reduce their failure rate. Some are blowing an LM350K regulator and opening up a 2.2K resistor which is in series with the regulator. Some failures are with the head end and the bridge rectifier gets destroyed so the power supplies blow the main fuse.
So I’m going to start working on some protection methods to keep the failures limited to dropping them on the floor.
Thanks again for the newsletter. As usual, well written.
Nice to know you and your background in electronics. You are smart to put in all the protection circuit otherwise there would be lots of bad equipment for you to repair. Keep up the good work!
hi jestine i am looking to buy a digital scope for my home and put together a home lab for my retirement time i never heard of atten from china and i know you visit the area is this epuipment ok will not use daily was thinling 40mhz for the tvs is this enought for lcd monitors thank you russ
I suggest that you get a 100 mhz so that you do need to upgrade later. I have ATTEN vga spiltter and the quality were very good. I guess Atten Scope should be reliable too.
Hai Justine, saya ada membaiki sebuah TV jenama Sharp 21 inci yang tiada display sewaktu switch on.Bila saya adjust kat bahagian screen di flyback di paparan keluar satu line horizantel warna putih.Saya telah
Adakah anda dah check IC supply voltage? Kadang kala vertical yoke coil rosak (open circuit) pun boleh menyebabkan one horizontal line.
2. Saya tengah membaiki crt monitor jenama IBM yang tiada power.Selepas saya troubleshoot saya dapati HOT dia shorted so saya tukarkan dgn HOT yang baru tapi bila saya switch on HOT tu shorted semula selepas beberapa ketika.Apakah yang menyebabkan HOT shorted semula?
Sila masuk laman web ini http://www.jestineyong.com/?p=403
Thanks to you I fixed my first Acer 17″ monitor. Replaced the caps and that was it.
The problem is no output when the 5V (22A main output) feedback circuit is connected to the SG3525A PWM controller IC inverting error comparator input (U5 pins 1,9). When I disconnect the feedback input the power supply outputs higher voltages on the outputs that do not have additional linear regulation. The 5V output is 24V and the 24V output reads 69V with no load. Is this what you should expect when the feedback loop is open?
Yes, in some design whenever there is a resistor open circuit, the output voltages will shoot up. In other design, the power supply will blink and may be shutdown
I am going to try with 10W resistive dummy loads and check with the feedback circuit connected and disconnected. Any other ideas? I have disconnected the o/c, o/v shutdown circuits.
I suggest that you check all the components in the feedback circuit since it does not contain lots of components.
can you please explain to me on g2 and the heater on my problem
G2 or screen is the red cable of flyback transformer and it can be varied from 0 to 300 over vdc by turning the screen pot behind the flyback. Heater is required to heat up the cathode so that the electron can be release in the picture tube. Tv use 6.3 vac from flyback and CRT Monitor use 6.3 vdc from power supply.
hi! how to determine the ABL in the plyback?
Connect two analog meter like battery and set to x 10 k and check from anode to any one of the pins in flyback. The one that show a reading is the ABL pin.
1.Bagaimana nak check dengan meter B+ voltage dari SMPS ke flyback primary transformer?
Dgn menggunakan meter. Black probe ke ground dan red probe ke B+ point.
2.Boleh ke diode FMS IN5817 gunakan diod yang mempunyai part number yang lain?
Ia anda boleh mencuba IN5818 ataupun 1N5819.
3.Anda mengatakan vertical yoke coil rosak (open circuit) pun boleh menyebabkan one horizontal line.Jadi bagaimana caranya nak
mengesan kerosakan vertical yoke coil menggunakan meter?
Check dgn ohmmeter.
Spare part ini ada jual ke dikedai-kedai .
Biasanya tidak jual.
sir thank you for the information how to buy your books.
You are welcome!
Sir I have a question Re. AOC LCD Monitor Model LW98+
This LCD Monitor are use in Recording Room,Last sunday the monitor has a Problem
there is a standby power but the screen white at the same time saw many vertical lines, and then I unplug the Monitor for about 30 minutes and plug it again normal ,after 5 min same problem. I open the LCD I Found out one of the capacitor in the power supply deform the value is 150uf/25v 105c I replace 220uf/25 85c,when a test LCD with new capacitor same problem occur. this Lcd has external power supply 12v. Or there is another Problem!
Check other filter capacitor with esr meter and for dry joints. Sometimes a loose connection cable between the mainboard and the lcd panel may cause such problem.
I have good news regarding the SMPS repair which we corresponded in our email. I finnally had an idea to locate the bad components. The two MOSFETs gone bad and I am replacing them. These two components cause one of the diodes, the bridge rectifier as well as the big filters act like open circuit. I, first, thought it was the bridge rectifier and transformer. After removing these mosfets the diode, filter cap and bridge rectifier (when tested with resistance method) keep quiet.
Now, what I would like to know is about the Thermistor that was blown up during my test. Is it OK to put it back instead of using a jumper? When I tested, it showed continuity so I thought it would be like a jumper.
Yes you can put in a jumper but the power supply is no longer surge proof.
With these SMPS repair experience, I also got another idea to locate the bad components on the LCD interver that I reported to you with picture before. The problem was the two SMD Mosfet on the power supply line. I am odering the parts and I am very reluctant to put on it.
Sometimes in this repair field we have to take risk so that we can learn what works and what don’t work.
As always, I am thankful to you for your ebooks and email support. I have been having fun finding out the culprits on the circuit board just like a cop in the town.
You are welcome!
Hi Justine i wanted to thank you for sending your reports,
they are very helpful.My lcd monitor is flickering and it changes
the brightness.When the flicker starts it affects the brightness.
Could it be the lamp?
Yes it can be the lamp or bad filter caps or even dry joints.
Actually I want to ask you about laptop repair . I already fine the faulty part than already replace but before replace that part no power When you turn on than after replace one faulty diode there the power is turn on Than after a few second the power turn off automatically something like NO/NC contact Do you have any idea some solution to check? Hope fully you opinion to assist me on To solve the problem
I guess there might be still some bad components in the board since you said you already replaced the diode. Trace along the diode and see where the line go. check all components related to that line particularly on the smd resistor. If all tested okay then i guess you may need to replace the power ic.
im a bit confuse about it. you mean connect the two testers in series connection to determine the abl?
connect the black and the red probes? then the remaining test probes will be connected to the ground (black probe) and the red probe will be for the terminals in the plyaback?
First connect the red probe to the black probe of another analogue meter. So now you left one read and one black probe. (is like connecting 2 batteries in series). Now test the flyback anode to any of the flyback pin either ways. If the flyback pin shows two reading (one high and one low reading) then that pin is the ABL pin.
Yes I have replace the vertical IC output section, bad caps changed, dry joints all resoldered, but still the same even changed one bulged capacitor in the CRT section. By the way Jestine how to check and make sure the supply voltage to the vertical output IC is good and stable?. Can Jestine please show me how?
Thanks Jestine & God richly bless U and Family.
First find the spec of the vertical IC and locate the supply voltage pin. Then place your black probe to cold ground and red probe to the supply pin of vertical IC and read the voltage. If the voltage is good and stable then directly replace the non-polar caps around the vertical ic output area.
Thanks Jestine,if it is the lamp how do you check them?
Do you check the caps and dry joints and if there ok replace
I used another working lamp to check them because lamp can’t be tested with a meter unless you have the lamp tester. If all check to be good then i will suspect the lamp.
I successfully repaired the TV SMPS and already returned it to owner (a friend of my wife). Thanks again for the ebook.
Dear Mr Jestine,
I want to ask about crt monitor.
First this LG Flat 15″ monitor is dead with tick..tick sound
and using your testing method i foud that the STK630 FET is shorted.
After I replace the Fet the monitor is ON, but the display is white bright and blank, with the left and rigth side is moving,sometimes wide,sometimes narrow.
Can you tell me what I have to check sir? I believe you have ever face this kind of problem. Please help.
Thanks in advance.
White display can be G2 set to too high, G1 negative voltage too low or even missing supply voltage to the CRT board especially the pre-amp IC.
How you doing?i hope you doing well.
I’m fine thank you.
I need your favor regarding the tv repairing. Fyi, i am still beginner in this field. I have one set TV 29′inch model Quayle that was no power. I already check the HOT area and it going good, but the filter cap kept the voltage around <200V. I suspect the power transistor is not working and it true.
It can be open start up resistor or even bad power ic.
The part no is D5036. My problem is i can’t find the specification thru the internet. So i hope you can suggest what the suitable replacement. Is it D5703 and D5702 can use as replacement?
Sorry i have no info on this too. However, from some of the website links that i found from the internet, they said the replacement number can be d5038,st8812fx and Bu 4508dx.
Very thankful to you. I found 2 open resistor with high value (supposed 220kohm) then i change it and it working. Again thank you Jestine!
what is pattern generator and how it is used in troubleshooting in Tv
It supply the appropriate signal (test pattern) so that you will know which section have problem when you look at the test pattern. If the test pattern curve inward or outward then you know it is the pincushion circuit have problem.
hi j.yong thank you for your news letter its very usefull to me its
helpfull for my carrier j.young i have one problem samsung samtron
45bn model crt moniter it have the problem is the width of the screen
is very high it dosnt control by using the control panel switches
what is the problem pls reply me thanking you
Try check the modulation diode that is nearby the flyback transformer for short circuit. Check also the pincushion transistor that is located at the heatsink.
Help me sir,…I can’t distinguish between hot ground & cold ground clearly on the computer main board —– ???
Computer motherboard do not have hot and cold ground. The hot ground only can be found in switch mode power supply primary circuit. Computer motherboard is all cold ground.
I finally found the spark spot, that was nearby the bridge diode, there was a pile of black carbonized dirt causing a hard short, the spark spatter even reaching the blue non-polar caps ( see the doc ). That is why I used much time finding the culprit.
You can use thinner to clean the area.
Now the monitor is ok, but the moment after powering it on, the display (with signal) shows but with horizontal scratch / wave full occupying the entire display; only after about 3 minutes the display would be normal. What is causing this？
It could be some carbonized dirt that causes the problem and you really need to clean up the board. If possible you can use a pen knife to cut out the carbonized area.
I had taken the photo, but cannot show clearly the problem. Also from the picture tube ( right beneath the flyback anode ) there is faint noise. What is causing the noise? This kind of noise I often hear from many monitors, but seems have no effect to the display. How to eliminate the noise?
The noise may comes from the yoke coils and there is no way to remove it. Sometimes the noise can be cause by coils underneath the picture tube. So you need to listen it carefully. If it comes from the coil then you can dip the coil into shellac for few minutes and then let it dry for few days and the noise will go away.
i would like to thank you so much for this service.it really helps me to
develop my career tips and handle electronic repairs confidently.
You are welcome!
i have few questions about trobleshooting this; an LCD monitor having
vertical dark lines on its screen-which components are likely to be bad?
It is the lcd panel.
The other is a crt monitor with bright horizontal line dividing lower dark part
and blurred upper part.
Check the vertical output ic , dry joints and supply voltage to the vertical output ic.
i also have a DVD with low output on 12v (+) and (-)
supply from smps but the optoisolator is okey. much appreciation for your help.
I guess you need to check all the components in the power supply. Check the filter cap with blue esr meter.
Sorry for asking so many question too you. But I don’t have friend that kind enough to give me information about monitor repair.
Sir, what is the problem when I replace SMPS using 18 volt zener when it is suppose to be 6,2V zener?
What is the problem when I replace using 6,2V zener when the actual part is 18V zener? will the SMPS blow?
You place the 100 watt bulb inseries with the fuse. If the bulb did not light and you got voltages at the secondary side then it is safe to put back the fuse and turn it on.
When do we must discharge the tube? Do I have to discharge the tube when resolder the crt board?
For CRT Monitor you don’t need to discharge but CRT TV you need to do so. You need to discharge whenever you want to open up the anode cap from the tube.
Is it safe to touch the flyback pin when the tube is not discharge?
Yes it is safe.
I try to turn on the monitor using light bulb series, I use 60W bulb,but the monitor cannot on,
After I remove the light bulb series and I connect directly to power, the monitor is ON.
What is the correct watt of the light bulb so that the monitor can ON and Safe,
cause in your ebook you said 100W should be enough.
It depends on the size and design of the Monitor. 60 watt supply too little current thus it is not enough for the smps to work.
Sir, I have a crt monitor that only have one bright horizontal line accross the screen and below the horizontal line
there is a gray shade about 2inch, and the other is black and blank. Can you tell me which part is the faulty?
Vertical ic output area. Check for dry joints, bad vertical output ic, bad corresponding components and make sure the supply voltage is good and stable.
Is it okay to turn on the monitor in that condition while I check the voltage?
Yes you can but you need to dim down the brightness so that it won’t burn the tube with a burn mark
Is it the vertical section? but why the screen is blank and rather brigth?
Yes it is the vertical section. It depends on which area that failed in the vertical section. Remember that inside vertical IC have lots of components.
Hope you are well..
I’m fine thank you.
I have just got myself a techtronix 465B 100mhz oscilloscope ..
Nice to know that.
Now i would like to get an isolation transformer but not sure which to get or where to get one..Do you have any suggestions for me or any links to any that would work with my scope ?
I suggest that you check from your local supplier to see if they would make one for you. Many electronic shops do not sell a ready made isolation transformer.
I am from the
Since the isolation is heavy thus ordering it from other country would be very expensive.
Also while on the subject of testing ..When you come across a monitor ( i have a compaq monitor that uses a benq pcb) now i wanted to test out some voltages with dvm but the board has components on both sides i.e a couple of voltage regulators facing the panel and there is a connector on the main board that connects to the panel from underneath the board . how would you go about testing any components with power on but board facing where you cannot probe ? do you solder a piece of wire to the component and test that way ?
Yes you are right, i solder a wire for testing.
There are also some ic’s on the same side so what is the best testing method when you come across these situations ? Maybe you could give a few examples in one of your reports or on your blog with tips regarding these type of situations as it would help the newbies like me and others that only have your ebooks to learn from as the ebooks i have from you do not really cover this type of situation.I know we have to come up with ways when faced with this type of situation but it would be a big help to know how a pro like yourself gets around this.
Same as above, for testing IC i just solder a wire to the supply voltage pin and a wire to the output pin (to check the waveform). You can also trace from the smd ic pins to see at which big components leads that it is touching. From there you can place your probe onto the big components directly from above the board instead from behind which is difficult to do so.
Have a good day!
This is Humberto I purchased an ebook from you awhile back and have learned a lot from your websites and blogs.
I had a question about uninterruptible power supply repair(UPS). Are these units worth repairing?
Because of the low price of the equipment and the high price of the UPS batteries thus it is not worth to repair it.
Should I spend time learning these circuits?
If you have the time you can go ahead to learn all the circuits in UPS.
I have a doubt as to how much time I should spend on a $500 UPS unit. Thank you for your time!
If all the UPS is high end type then you can start to learn this circuit.