Hi. I was reading your article about how to repair an ATX power supply, but can you please tell me in which points of the output supply do you measure the output voltages?



Hi David,

I measure all the points after the secondary side diode. That means the cathode side of the diode.




I am karthik now iam doing B.E EEE i like electronics works from my young age when i was studying tenth standard i visit many electronic repairing shop and ask them how this circuit functioning and if any problem means how can i identify it and how to test the troubled electronic component some one would explain a little bit ideas and many of the techniciens neglected after that incidences i will search every were and refer some electronics books that will give me only basic ideas after these incidences i have crossed the preview of your e-book testing of electronic component i was suprised and after reading the complete e-book i have got the confidence and i starts to  trouble some simple electronic components like FM and some AUDIO AMPLIFIERS and some CELLPHONE CHARGERS successfully my thoughts encouraged me myself

Hi Mr. Yong,
Thanks for this useful article.
It makes me want to ask whether you have the guide for replacing sony vaio laptop E series lcd screen?
I have mine which cracked due to car accident and I brought it to sony service center to be replaced. After replacement it worked well but I didn’t notice that the lid sensor was not working. I assume it comes from the connection to the sensor near lcd.

If you have the article, it would be great for me.
My laptop is Sony Vaio VPCEB37FH.

Thanks and Regards,


HI Andrie,

Sorry i do not have such article on the lid sensor. You can send back to Sony for warranty claim because if the lid sensor is not working, you may have power but your screen may not come on



Hi Olaoluwa,

Thank you for the SMPS repair guide,i have gained a lot from the book.

You are welcome!

please sir i need your adivce/support on how to solve the power problem of this lcd monitor(dell 1905fp).the problem of the monitor is NO POWER(it does not not turn on at all).i have carried out the following tests as explained in your SMPS repair guide.

1–Blue Ring Test:i tested the primary winding of the smps transformer and all the LED of the ring tester  were ON which indicates that the power ic ,primary winding and secondary diodes are okay.

2–Flickering Test:i removed the smps transformer in order to know which section is faulty,the needle of the meter flickered which show that the primary section is okay.After this test,i tested the output voltage of the secondary diodes.there are three(3)shokky diodes in the secondary section.

Diode 1:it gives 5.42volts without load(mainboard) and also 5.42V with Load

Diodes 2:it gives 13.07V without Load but gives 19.40 with load.

Diodes 3:it show only 1 on my digital meter both with load and without load.So  i suspected this  number 3 diodes.i removed it from the board and tested it but it was okay.

so i put it back into the board.after this,i then carried out the resistance test.

from the resistance,it showed that there is a  problem in the output line of Diode number 3 because when i did the resistance test,the pointer flickered toward infinity while the pointer flickered  towards zero ohms in the case of diode number 1 and 2.i have tested almost all the components in the output line of diode number 3  but i did not see any faulty component and i do not have the schematic diagram to trace all other component.i would be very grateful if you could guide me on how to make further test.

thank you for your usual support and understanding.

best regards.

Please if you know where i can get the schematic diagram,kindly link me to the web site.thank you.
From your description it seems the power supply is working because it could produce some output voltages. If you did not see the power LED light up this could mean there is no signal coming from the MCU mainboard. What you need to do now is to make sure the mainboard is getting 1.8v, 2.5v, or even 3.3 v from the voltage regulator ic. The supply to the voltage regulator ic is from the power supply. Assuming if all the ICs in the mainboard are getting the right voltages, this mean the MCU could have problem.

Please update me on this repair case-thanks.




Hello Jestine, you should make a book about fixing mother bored lines. Currently I have this problem were my lines are broken, I have a conductive pen to reconnect but it’s making a mess, I don’t know what else is out there to fix it. Can you give me a tip?

Hi Alex,

Use the smallest single core wire to join between the two points.




Hi Justin,

I was hoping you could assist me with the diagnosis on this particular model Sansui SV -EPD 4206, plasma TV.  The display is covered with black patches/spots when you switch the set on and as the TV warms up gradually disappears. Could it be a gas problem from the display?

Please find four photos attached to illustrate the problem.

Hope you can assist.

Hi Jan,

It can be the panel problem but first you may need to use coolant on the z sus board if the sansui panel is LG. If it is Samsung or Panasonic panel you may need to check the x sustainer board  first. If the problem gradually disappear the quickly spray on those board with coolant to see if the problem comes back or not. If the problem eoms back then you know the problem is in the board and not in the lcd panel.


Dear Sir   please let me know how to repair ups for computors, problam is out put from ups is 170v ac, as soonas power failure occurs, battery used is 12v 7amps.new battery replaced      ups is apc-500

I dont have any ups ccts,

Thank you

Hi Karunanidhi,

Sorry we do not really focus on UPS repair because the price here is very cheap. Usually what we do here was to replace the UPS batteries and reprogram the EEPROM IC. In your case, if all the components check to be good then it may be the EEPROM data had corrupted.



My dvd player dosen’t on, when I open it I found out that one of the capacitor has swell up. Value of the cap. Is 47uf 400v then I replace it with 22uf 400v can it work


It is a bit low. Evehn if it can work I’m afraid it may have some ripple. I suggest that you replace it with a higher cap like 68uf 400volt.


HI Gill,

This is Gill from Coconut Creek, Florida (USA).

How are you?

I’m fine thank you.

I bought your e-book “Troubleshooting & Repairing Switch Mode Power Supplies”, some time ago.

I really enjoy this e-book for the top notch info you put together with it.

I’m already having a fair amount of success in repairing LCD and Plasma TVs sets based on the information in your book.

Thanks and congratulation on your successful repair.

but once in a while, as you know we bump into a “tough dog” (hard problem).

Most repair tech will encounter this kind of problem.

I’m trying to fix a Samsung LCD TV forty inches, that the relays keeps clicking continually, and never turns the tv on.

By checking the power supply, I noticed that one of the terminals for the power transformer had a “dry” joint. There is no

bulged caps. I resoldered the terminal, but the problem is still there.

I would appreciate your thoughts regarding this problem.

First you need to check if all the voltages from the supply voltage good and stable or not. If it is stable then the power supply is good. The relay have clicking sound most probably the signal coming from the MCU fluctuate and this cause the small relay driver transistor to open and close continually causing the relay to have clicking sound. You need to make sure that the supply to the MCU is good and if it is good then most probably the MCU have problem. If you have the scope try check if there is any sine wave at the pin of the crystal oscillator at the MCU.

By the way, any new e-books from you, that I still don’t have?

Thank you very much.

have a nice day!

Not at the moment but my partner is coming out with a printer head repair ebook soon.

Have a good day!


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