HI Luiz,

Hi Jestine, thank you so much for you answered me.

No problem.

You ask me, if after or before  of using  isolation transformer in eletronic repair, I mean after , when my isolation transformer is ready and I’ll be work with it on smps (for example), I’ll safety about electrocution, if (how I said),

-> if my hand accidentally touch the point that measure 500 VDC (after PFC diode) , I will not feel this 500VDC!!!!???? I will not electrocution!!!!????

Assuming you have used the isolation transformer and accidentally touched on the voltage, you will still feel the pain but very slight pain but you will not get electrocuted.

and please one more question:

-> the use of oscilloscope powered from the same isolation transformer , and, (as you said), “Yes it can ….. I used to connect this way”.

Now I ask you , “it can”,  but not necessary…(the oscilloscope can be powerded direct from AC) ….

or  “it must (obligation, absolutely necessary)” be powered by isolation transformer, by the same (as you said), or any one, since that has an isolation transformer??

Yes you are right if the smps already powered up using isolation transformer then the oscilloscope can be directly connect to the ac main.



about 20 years ago a older tech was testing some rf transistors (out of curcuit )with a scope.even though they tested good on a radio shack transistor tester he checked them again with a scope and 2 of 10 showed a pattern with a curl .he told me these were bad.i can,t recall how the test was set up.do you know how? regards s.w.r.

HI Sherland,

I’m not sure if this the one you are referring to:





Helo Sir,

I am a computer hardware technician and would like to study electronics for motherboard troubleshooting. I mainly service laptops and in search of a good multimeter with everything i need for testing motherboard or any electronic circuit. Heard that “FLUKE” is a good brand but i am confused to select one from my nearest showroom because there are somany models with same functions. Please advice a specific model for my use. price no matter.

Here is my nearest showroom’s website link for your reference  http://radionics.rs-online.com/web/c/test-measurement/multimeters/

Awaiting for your valuable reply


You can select the one that have the ohm, current and voltage range and it can be from any other good brand like, greenlee, Sanwa, Kyoritsu and etc. It all depends on your budget. Besides a good multimeter you also need

Blue ESR meter
Digital capacitance meter
oscilloscope and
Smart Tweezer.



HI Boling,

Thanks for the praise.

You deserve it because of a never give up mentality

Sorry, I mean the blown 1000uf 16V e-cap was ESR tested well, so are the dual big filter e-cap. Actually, now all the sets use the original dual big filter e-caps, the rubycon is only used for revealing the hidden problem. If there is a special capacitor tester that can test ESR, capacitance & voltage rating ( 3 functions ), that will be great for repairman.

Yes there is one but very expensive Sencore LC103. It can also test coils/inductor.

By the way, do you have ATX power supply tester, could it be like testing with real load?

Sorry i do not have usually i will use the motherboard and harddisk as load. You can buy one and test and see how accurate this tester is.

Have a good day!



Hi Jestine Yong
Thank you for sending me the site of repair of the print head, but right now
I’m interested in how to open my transceiver GP-78 to try to fix it because it
crashed and I would like to fix it. Does the friend has some tips on this equipment?
Thank you and see you soon, keep watching their site.

HI Dilermando,

Thanks for your email. Since i have never repair such device before thus i can’t give a direct answer on how to open it. What i can see is that usually this type of device have a clip or lever that is located inside the casing and it will be hard to open it if one does not know where the clips are? Sometimes i do came across lcd monitor that do not have screws and all of them have the internal clip to hold on the cover. Trial on errors that have made me to successfully remove it.



HI John,

what is the best or easiest way to find a short circuit on a circuit board.

It depends on what type of board and what kind of component shorted. One can use an ohmmeter or specialize equipment like leakseeker 82b from EDS.

My PSU continues to supply power but there is nothing connected.

cause of the problem: too much voltage

Some power supply design will produce output even though there was no load. You need to connect to a load in order to test the output voltages.


I have a power supply for 2 in VCR AND DVD there is no power on the Seconary side and when i put my Multimeter on the mosfet 2SK3566 smoke come from the power supply board and if i check the brige rectifiers the volts change up and down could it be the mosfet is faulty and when I first put the power on the transformer has a nosie for 5 sec then stop

HI Warren,

First you need to power off the set in order to test such components unless you are really sure about how to perform the voltage test because a slight mistake could it to have problem. I guess in your case, since there are components shorted, check all the components in the power supply which include the secondary diodes because a shorted secondary diode could cause the noise problem.



Hi Sohair,

I am so glade to receive your mail,but  I am so sorry because I haven’t time to write  to you  continually . Every time I have chance to be free I harry to read your mail with pleasure to obtain more information.

No problem.

Now I need your help . As you know  I work in repairing electronic cards and systems in different branches of industrial companies , I mean that repairing any electronics cards and different types. Most of them without circuit diagram and sometimes old fashion ,I lost more time to translate it from layout to circuit diagram to analysis it and repair it after that.

Now I have converter I think that it is Italiano from the data on it ( convertitore AC-Dc .4     livello A   TASK84  SPA ) , I drew its trigger circuit and module of thyristor and change some fault ICs

. Then measured the dc volt of the card , every thing is OK but there is no out put DC volt to operate the load (  dc motor).

Believe me I made all my best on it and the customer is very  sad because of his factory ,I want to help him .Please try to send me help to complete its repairing.

As you have said card is harder to repair because of lack of information. Since you are repairing card i suggest that you get a HUNTRON tracker from
huntron.com to compare the signature of the card. Any differences is the clue for you to start troubleshoot it.



Dear Jestine Yong

Thank very much for all your attention to me.

Now I got a problem and want to if you can be of some help.

I got a LCD HP ZR24W monitor from a customer and the problem is as the following:

When connected to the Central Unit it displays correctly et can work perfectly. But it can keep working for about 30mn and everything disapears from the screen but the power on led we be still on .

Is tried to test all components ( resitors, capacitors, diodes) et everything seems normal but the problem is steel there.

Do please of heping I with your suggestions.

Best regards



HI Adama,

No display after 30 minutes. Ok first is all the output voltages good and stable. Next make sure no dry joints in the high voltage transformer. The next thing you need to check if there is any dc supply voltage to the inverter ic or not. If there is no voltage suspect the MCU in the maiboard may have problem.



Hi Jestine

Hope you are having a good day

I am trying to repair a Panasonic tv which keeps blowing the H.O.T.immediately. I have tested the transformer using The Blue Tester and it tests O.K . This transformer has a split diode secondary and I was wondering if this test is accurate on this type of transformer from your experience

Thanking you and keep up the good work



HI John,

The tester is for checking on the primary winding only and does not include the diodes. You can visit the link below for more information:




I have a Staples SP1706 monitor. That has me stumped. Using your course I have fixed about 10 monitors, mostly for myself and friends. However this Staples monitor got me. The power light is on but the screen is black.I looked at the screen with a flashlight to see if anything was there, nothing. I can not find who manufactured this monitor , therefore I can not get any information on this monitor. Any information you can give to me about this monitor would be greatly appreciated.

Thank you.

Anthony Dean

PS: Your course is great.

HI Anthony,

Thanks for the support. In your case, try measure to see if there is any supply voltage to the inverter ic. If no supply voltage chances is high the MCU in the mainboard could have problem, Before that make sure there are right voltages entering the MCU and make sure there is sinewave in the MCU crystal. Keep me update on this repair.



Dear Sirs,

I’m a regular reader of your news letter.Sir, I’ve a approx. 15 yrs. of hands on exp. in repairing of electronics appliances. i also have an exp. in teaching electronics theory & practical in various institutes. I wish to start my own electronic training center. pls, guide me how to start, manage training center. Your valuable support is most precious for me.

Thank You.

HI Abhay,

You need some model like buying instruments, tables/chairs and you need to prepare a workbook for your type of course. Before that you need to do some survey to see if there is anyone interested in your course and if they are willing to pay for it or not. You also need to have a marketing plan like how to make your courses known. Marketing is the hardest parts among all the above. Managing the center will come in later part as if the courses grow you can hire more people to take over some of the task.



Hi Jestine,

I hope you and your family are fine.

I have an electric bread toaster that keeps tripping the power circuit at home whenever I switch the toaster on.   I have both digital and analogue multimeters, a 30MHz Trio oscilloscope and a function generator (I doubt i need the last two equipment to troubleshoot, har har!)

Please give me some troubleshooting tips. thanks!

HI Arjunaidi,

Tripping means either the live wire shorted to ground, neutral wire shorted to ground or even live shorted to neutral. I suggest that you open up and check if the filament in the toaster shorted to the body or not.

Set your analog meter to x 10 k ohm and measure the live/neutral to ground to see if there is any reading or not. It should not have any low reading. Make sure you turn on the toaster (without power) switch check it.



Hi Justin,

Saya mahu tanya, jika LCD monitor on dan keluar gambar dan dalam masa 3 saat lcd automatik off.


HI Hasnol,

No problem krn ia datang dgn support saya. First, make sure ada bekalan kuasa ke supply pin inverter ic. Check dan tengok samada dry joints kat kaki high voltage transformer ataupun sekiranya ada electrolytic capacitor yg dah bengkak. Sekiranya semua test ok make salay satu backlight dah ada kerosakan.




Hello Jestine

I have a monitor speaker which has sound output is distorted. I did test all the capacitors around sound amplify and I did find anything faulty. what should be the problem on that monitor speaker of mine?

I need your advice please!

Kind regards


Hi Esther,

If the components checked to be good then you either direct replae the sound/audio ic or check if the supply voltage to the audio ic have any ripple or not (by using scope). The supply voltage has to be good and stable.



HI Boling,

I have solved this CRT “sering mati” problem as it is written on the picture tube, but the image is asymmetric vertically. How could I make it symmetric?

Try check if there is any bad components surrounding the horizontal linearity coil. If can, try place the horizontal linearity coil the other way round and retest.



Hello Mr. Jestine,

I am facing a problem with Samsung syncmaster 15″ monitor. The problem is, when i switch on the cpu the monitor indicator blink and no display but when i unplug and replug the power cable of monitor, light comes normally and run as usual. This happens every times when i switch on the computer. I have seen this type of problem in about 2 or 3 monitors but could not guess the faulty section. Please guide me in which section i have to check and what type of component may be faulty.


Gopal Sharma

HI Gopal,

This can be the problem of bad Monitor CPU. Before that make sure the output voltages from the smps are always good and stable. Make sure also the CPU is getting 5 volt.


Hi Jestine,

I am planning to buy your SMPS ebook this month when I get paid. Hi really got my “moneis wrote” after reading  the first ebook on Testing Electronics Components. Jestine, I need an Ebook with more info doing voltage testing. The bonus book on Voltage Testing only wet my apetite, I need more info on voltage testing!!

Jestine, I must say that your ebook really help me. I love it…….



Justine, Saya sudah check semua E-Cap dan tiada yang bengkak atau bocor. Jika salahsatu backlite rosak, bagaimana boleh ok dalammasa 3 atau 5 saat selepas itu blackout?

HI Hasnol,

Krn ia ada feedback circuit di mana backlight yg lemah ataupun dah rosak tak akan hantar isyarat (dlm miliampere) ke feedback maka feedback circuit ini akan hantar isyarat ke inverter ic dan suruh inverter ic padamkan waveform generator ke high voltage transformer. Kalau tiada waveform maka high voltage tak akan berfungsi dan high voltage akan turun balik pada kosong volt. semua ini berlaku dlm masa beberapa saat sahaja. Itu sebab anda dapat lihat gambar dan selepas itu terus padam.


Comments are closed.