- Short Circuit FinderPosted 4 years ago
Electronic Repair Questions/Answers and Testimonials- Part 53
Dear Mr. Yong,
Thank you for your excellent and so interesting blog, I follow it daily waiting for new posts. Thank you for very informative newsletter too.
Good day sir, i downloaded the ebooks from the link you gave me and i have been reading them, the material inside are very rich. I am a repairer but what i discover in your book is amazing, i am encouraging you for the hard job you are doing God Bless you and your Family.
Ustad (teacher) J.Y.
Thank you very much for your news letter and sharing your experience as well as detailed guideline for your LOVERS.
I am attached to this field probably since 1974 and still learning. I am not praising because you send me newsletter but your are sharing your valuable knowledge without any hesistation and helping people/students so that they are successful in this field.
I pray for your good health.
With best wishes
Hope you don’t mind me asking another question..
I have a psu that i have taken apart as i have had an intermittent fault with it..So i decided to test most of the components in it either by soldering out one lead or completely removing it and testing..
Now i came a cross some schotty diodes attached to the psu heat sinks ..3 on one side and 2 on the other..
There is 3 bigger schotty’s and 2 smaller ones..now i did your testing method from the schotty pdf i got from you..
Used analogue meter ( exact same one you have) at X 10K red probe on middle leg(cathode) and i touch black probe on both outer legs (anode) and get the right reading pointer full deflection ! then i reverse the black probe to centre leg and red probe to outer legs ..pointer moves up just a bit ..so this is a good schotty diode right ?
You are right. It is good.
Now when i tried to take a reading as above on the smaller size schotty diode ( marking on diode is STPS20H100CT )
I get the pointer swing full deflection when red probe touches middle leg (cathode) and black probe on each outer leg ..but when i reverse it by putting the black probe on middle leg (cathode) and red probe on each outer leg i am not sure that the pointer moves because it is so small a movement i don’t know if my eyes are playing tricks lol.. If my eyes are not playing tricks then the pointer movement is less than a mm if that .. hope you can understand what i am saying only it is hard to express it in an email..
So my trouble is now ,is this a good schotty if it did move by a hairs width ? Have you come across this yourself when testing ?
They are good schottky diodes even though it moved a little. If it swing full scale when black on the middle pin and the red on the other pins then it is shorted.
Now the psu problem is intermittent like i said it will power and start up my pc then when i turn the pc off and try to restart it will sometime work normal and other times it won’t boot the pc..
It may be the problem of a start up resistor and sometimes a bad POWER IC may cause such problem.
I am in the process of changing out all the caps apart from the 2 big main filter caps so i thought i would learn to test while i have it apart and put use the great ebooks that i got from you..I have never studied electronics as stated before so i am learning every day thanks to your ebooks that guide me.
You are welcome!
Just one more question if it no trouble ..when testing smd components like caps,resistors and diodes (this psu has some smd on the pcb) do they also have to be soldered out when testing .
Yes you need to if possible.
Thanks once again Jestine for all your help as it is much appreciated.
You are welcome
I have this question for you. I am working on a ITT dvd player..one of the expensive one actually. I found a dead short in the power supply and one of the shorted part is a mosfet 900 volts 9amp. I got a new one in 600 volts but 20amp mosfet. it is a brand new but but strangly when I get the whole circiut with the lopt/FBT with the mosfet on, it gives me only four bars… but when I take out of the circuit, it gives me a full bar? I find that really strange since it is a good and brand new one..any ideas?thank
Thanks. Have you check all the components in the primary side? In some SMPS design, the tester may act this way. If you have confirm that all the components in the primary and secondary tested good then go ahead to on it.
hi Mr yong
I have a problem with one of the printer power supply.i recently work in
burma as a hardware engineer for locals and NGOs in myanmar
as you know ,this contry is short in both supply and information.this PS
have some water spill during transport which the user does not notice
the water spill down to the bottom of the printer where the power supply
module is mounted.when the supply is powered,the regulator IC( i assumed)
and the FEDs in the sys goes out.as i examined,there is no other harm but
just the above mentioned prob;.the FEDs are replaceable and i can have them
local market.but the regulator ic with 6 terminal (and a heat sink attached
is not aviable in local market.there are no stock aviable like the hole PS
i need replacement for this ic.the ic is coded MIP0246SY 445R.it is not
included in ecg/nte or so so on internet.if you can (please) help me,mail me
or the main function of this SC or the terminals output diagram.with best
Thanks for your email. Generally Printer power supply ICs are hard to get. We also facing this kind of problem when repairing HP printers. Sorry i could not find those parts.
I have just sent you an email before this one , I have CoolerMaster SMPS product no : RS-350-PCAR-I3 350 276W it stops and dead it’s fuse is good and I tested the outputs and all is good expect the +12V nothing with it no 12V, may I start troubleshoot with the primary part or the second part ?
If all output are good and only the 12 volt line have problem then you should check problem only in this line. It could be dry joints, bad filer caps, bad output diodes and etc.
I have fixed an HP D5060a lcd monitor
The symptom was flickering
So I checked the inverter board for dry joints and found an inverter transformer was dry jointed
I re soldered all transformers .
It is working good now.
BTW a tip for ERG members
when I fix LCD ‘s I always re solder the transformers as it is high tension get quite warm & solder goes dull.
Thanks for the email. Yes i agree with you that one has to resolder the high voltage area as i came a lot of LCD Monitor with this kind of fault.
Jestin nice again,it is true ,microprocessors in smd form is difficult to fix,but we are lucky that they are not damage easy.
You are right!
Jestin i am stil study your smps repair book,i have it in bookform by printing it,so small small if i have the time i read it.
this book is also a master peace,i respect you verry wel,thats why i have again a tip for you .
Thanks for the support!
my friend ,listen you are a wonderful technician with ,experience, you are chairing /dailing your secret with technicians over the whole world. you are a very good man.i dont know how many members you have now, but i think you deserve an reward.
You are welcome. Currently have about 34,000 ERG members.
yuo are real a honey,s person,i mean you are not cheating people, I think mayby you can think about it to start from next year january with a small contribution for all the members,maybe 10 or 15 us dollars a year. This because every thing is getting expansive ,and to keep your site running you have to do this and so on.
Thanks for your suggestion. There is a website that charge USD7.99 for a question asked on electronic repair. But at the moment I’m still ok with the financial because my ebooks still can sell. Thanks for your concern too.
Have a good day!
I have a problem with crt color tv LG 21″model CF-21S32EX,the voltage
G2 of television increase and decrease frequently the light of tube of
picture increase and decrease consequently the light of picture that
saw of tv too,also the color of picture increase and decrease or or
sometimes total screen blue for instant again picture return,I was
tested parts of power supply ,b+,fixed and not changing also I varied
behind high voltage trans potentiometer(screen and focus)when varied
the potentiometer of screen the picture of tv bad and again problem
exist I replaced ic number tda8842 but again problem exist,i am
sending low resoulation film (3gp format) about this problem please
Try remove the G2 wire and test to see if it stable or not. If the B+ voltage to the flyback is stable and the G2 wire output is not stable then suspect a bad flyback divider. You may need to replace the flyback transformer. If the G2 voltage is stable then most probably along the G2 line there is components that may have problem especially the high voltage ceramic capacitor. You may need to direct replace the capacitor because the normal digital capacitance meter can’t really test if it is good or bad. By the way, sorry i could not open the video. There was an error that says video file not working.
Finished your monitor teaching course? Like to ask 1 Question. Any substitution for transistor A2039, Can U check for me please.
Thanks Jestine for your help & God bless
Just completed few hours ago. The substitution for A2039 is 2SA1244, 2SA1795, and 2SB1203
I have a 15” LCD Monitor HCM510 LSA, HCL make monitor which is having display goes after some time, I have corfirmed the LCD panel ok, problem in the conversion board, pls. gide me to repaire this board. I have cheked both mosfets in output section found ok.
Thanks & Regards
You may need to check the backlight because a bad backlight could cause such problem.
After few days-Michael sent me this email:
Replaced other working backlight tube, now the monitor is working fine, thanks for your valuable suggestion.
I have returned the set, without burning in and the next day the customer brought back this monitor.
His complain was the raster is getting stronger by itself without adjusting its brightness control after using for sometime, causing the color to be washed out. What is causing this problem? I’’ve checked all the caps on the CRT board.
If the flyback divider have problem it will slowly go bright. You may check the G2 voltage to see if it slowly increase in voltage.
I am disconnected g2 wire and measure voltage by voltmeter ac and
dc,varied voltage of g2 infinitesimal about mili volt and b+ fixed,AND
NO PROBLEM IN PICTURE ,
You should only test the G2 wire with DC voltmeter and not AC meter.
I connected again g2 wire ,and varied screen and focus potentiometer and problem again appear afterward
disconnected g2 wire,again problem exist but the light tube lower than
when connected g2 wire ,the voltage of g2 wire varied more than
ago(FIRST TIME DISCONNECTED),
Sorry i don’t get what you mean. If you have removed the G2 wire and the dc voltage not stable then replace the flyback. If the dc is stable then directly replace the high voltage cap along the G2 line in CRT board.
also I was measured pin of trans high
voltage namely ABL that go to pin (ABL)of ic TDA 8842,this pin of high
voltage varied too but in low voltage,
WHAT IS WORK THE PIN OF ABL?
Is to control the contrast.
WHETHER MY PROBLEM RELATED TO THIS PIN?
Your problem is screen bright and dim (raster) and not the wording bright and dim thus it is not related to the ABL.
Previously replaced TDA 8842 THEN MY PROBLEM IN HIGH VOLTAGE TRANS OR
IN OTHER PLACE !!!!!
DO YOU SAY REPLACE TRANS HIGH VOLTAGE?
I meant if the G2 dc voltage is not stable and the B+ VOLTAGE stable then replace the flyback transformer.
Hi Jestine Yong
Try check and replace the backlight.
Thanks for the april newsletter.Yong, just one to ask you one question.
Lets says,we want to remove the bad SMD ic in any of the main circuit board.so we will use blower, right.so was is the best temperature to set at blower,when we solder back the good SMD ic at board?
The temperature i usually set to 400 to 450 degree celcius. When we solder it back i just use my normal solder gun 25 to 30 watt will do.
Boleh you hantar gambar atau video ke e-mail saya, macammana cara betul untuk discharging CRT TV anode
Try view this video:
Is it necessary to pull the G2 cable out or just measure the G2 point on CRT board when checking the G2 voltage?
Have a nice weekend
Either way also can. However, if you suspect that the G2 line voltage down due to component breakdown when under load then you should test it off board.
Jestine could you recommend the right multimeter to purchase.Thank you.
Sent from my iPhone
For analog meter get a Sunwa Meter (must have x10k ohm range). For digital meter get any good brand like Fluke, Sanwa, and etc.
Hi, I’m trying to fix a CCTV DVR/monitor combo. I believe the flyback transformer is at fault. That’s what an electronics repair shop said. The part is hard to locate. I was wondering if it’s possible to disable the monitor part of the combo, and use an external monitor. Currently the unit doesn’t fully turn on.
Thank you in advance for any advice.
Thanks for your email. Since i have not modify this type of circuit before thus i could not provide any definite answer to you. However, if you could locate the right signals/voltages from the DVR then i guess there may be a chance that the Monitor will work.
Hi,how are you?Hope you always fine indeed.Thanks for the info about transistor c5707 in your blog.It’s a good post.Few shool in my area use lot of dell lcd monitor and they send to me about 30 unit lcd monitor symptom like this.But the problem is the spare part.So last school holiday i travel to few places for vacation and drop by at the electronic store and found out this transistor in kuantan for rm 7.00 ea,in Muar for rm 5.00ea but in Seremban it just rm 3.00 ea.At least the problem is solved.I’m gonna open my own electronic and computer shop in the end of this year.Hope everything going well as planned.Lastly can you tell me your experienced and advise about how you charge your customer base on job that you already done.Thanks for all the support.
Nice to hear from you and the Seremban electronic shop sell that part very cheap! I’m charging a customer on a flat rate basis. I’m charging RM100.00 for a 15 and 17″ LCD Monitor and this charge will inclusive of labour and spare parts. If i can’t find any parts and can’t repair the monitor, i will return the monitor back to customer free of charge. It is more like a give and take situation. Congratulation on setting up your repair business!
I saw a shop which sells the vertical half-cut flyback, just like the picture of one of your article explaining what is inside the flyback.
I wonder why the manufacuter make it like that?
Are you referring to the flyback divider (monitor blur buster)? If yes then the purpose of the manufacturer is to create the flyback divider to solve blur picture problem.
I read your book “troubleshooting and reparing SMPS” and learned many good information. now i begin to make tests on running atx power supply, i open one and testing the ac and dc voltage in the primary side which require to remove the board from the case to test the voltage over the filter. so i remove the 4 screws which one of them connected to the ground (green cable). and after i finish i dischage the 2 main filter and return the board to its location but i forget to fix the ground cable to the 4th screw. when starting the ps with shorting the green and black wires at output , i lost the fuse, 2 diode rectifier, 2 capictor and the 2 fet (short circuit). i search what is the mistake i do, nothing except forgetting connecting the ground green line with the screw.
do you think this is the true reason ?
I don’t think this is the cause of the problem. Most probably there may be something that have connected wrongly or it could be a bridge of solder underneath that had cause the power supply to blow. PS usually have shutdown circuit and if the green wire really shorted to black wire, the ps will shutdown and will not blow.
Where can I get a good zener diode tester. I dont want to build one.
So far have not come across any electronic shop that sell the zener diode tester.
when i power up the tv appear horizontal line in the middle of screen red and green tin color only.no rastar but the sound is ok…last night i try to replace the vertical and horizontal ic LA7625 but the problem cannot solve…at now when i power the unit the relay click but the lights from the crt neck is gone and the sound dis appears….
I guess there must be something that had wrongly done otherwise the TV should have the high voltage. When you said you heard a click only that means the flyback is not energizing. I suggest that you double check again or even put all components back to original and retest it. One horizontal line could be due to missing supply voltage to the vertical IC.
I have a Rca HDTV that was having a problem the picture lost its converence i bought a converence repair kit removed the bad compents and installed the new ones the tv worked fine for about 13 hours the picture went black and when i tried to turn it on all i would get is a the green light would come on for a sec and go off and come on and go off it did it 3 times and that was it someone told me it could be a bad capacitor or the flyback..
I suggest that you isolate the problem using the link below:
You may need to read this article as it can give some ideas to you:
Hello Jestine..Saya mempunyai sebuah amplifier jenama Pioneer dan masalahnya transformer dia rosak.Soalan saya dimana saya boleh beli alat ganti transformer ini?Model transformaer ini adalah XTT3006 TAM A M 0534.
Saya harap Encik Justine dapat membantu saya.
Biasanya parts untuk produck jenama, kamu kena balik pada distributor dan beli. Part nombor transformer itu sebenarnya adalah code sahaja dan tidak mencerminkan apa-apa spec tentang transformer tersebut. Sekiranya anda tahu tentang volt, dan amp transformer itu, anda boleh beli satu dari pasar road dan modify it.
I have a question?..,I have a 21 inch. SONY Trinitron television the problem is the video of this tv are not showing on the screen but the sound are good and clear…I thought this is a tube problem but when I put this picture tube on the old model SONY Trinitron television the picture of this tube are still good..is there any solution forthis?thanks a lot …..
Have you check the G2 voltage at the CRT board and make sure the tube is lighted up. If no light that means the heater line may have problem.
Hai Mr Jestine,Saya nak minta tips daripada Encik Jestine.Saya sedang membaiki CRT Monitor yang mempunyai masalah no display.Flyback ok,high voltage ok.Kemudian saya resolder bahagian komponen yang ada dry joint.Bila saya switch on monitor display ok tapi selepas tempoh 30 minit display hilang semula tapi LED dekat power button on/off still green.Saya berharap Mr Jestine sudi memberikan serba sedikit tips kepada saya bagaimana untuk mengatasi masalah ini.
Sekian,terima kasih atas setiap pertolongan yang diberikan semoga tuhan membalas jasa anda.
Kamu kena check G2 dan heater di bahagian CRT board. G2 kena ada voltan antara 250 to 300VDC dan heater mesti ada 6.3 vdc.
Hello Sir Jestine,
Thank you so much sir for sending me a repair newsletter it helps me a lot. By the way sir i have a problem of my Sony Television an older version around 2000 model. The problem is I replace the horizontal deflection output driver ( transistor 2SD1878 ) it works only around 30 minutes and again the transistor 2SD1878 is shorted. What might be the problem Sir? Please help me about this problem.
Thank you Sir Jestine.
Have a nice day.
Please check this link:
thanks for your time giving me suggestions. I do have a problem on fixing a LCD monitor, i got it from my friend, it is an old LCD monitor, but it’s dead now, when you plug the power (it’s a DC power adapter for this monitor), the power light is on, but no display on the screen. I dismantled the case and found two circuit pcb boards, for i have not repaired this before, and i barely have enough knowledge on LCD monitor, could you plz give me some suggestions on how to resolve this problem.
thanks very much
With power but no display can be cause by the mainboard or the inverter board. What is the color of the power LED of the LCD Monitor? If you know how to perform the voltage test then you should check on the mainboard and the inverter board supply voltage. Without the right voltage there will be no display.
One of the methods you use to repair SMPS in lcd monitor is removing the power transformer first befor checking the component. Can i use this method also when repairing atx PS ? and if it’s true, is this means removing the three transformer or just the big one.
Thanks for you comment.
If there is 3 transformers then the best is to remove the three to test out all components.
I recently got an NU model QL-711V lcd monitor that wasn’t working properly and upon hooking it up, I noticed a distinct burning smell coming from it.
I shut it off, disassembled it, inspected the board and immediately saw an area that was slightly discolored. I smelled it and it was indeed the area that was giving off the odor. There are two transistors located here, both labelled C5706. They are located on each side of a small square box with the numbers .22J100 on top.
Are these transistors known to short out and if so, do they take other components with them or will replacing them rectify the problem? From a visual standpoint, everything else on the board looks fine and all the capacitors look ok as well with no bulging tops.
These transistors are common to have problem and usually would take out other components too. Check the .22j100 volt tuning caps and make sure no dry joints.