Hello teacher,its Ajaz again with a problem of a german made tv.[BLAUPNKT] [MODLE IS70-51VT] [CHASIS NO FM412.40] I dont have its orignel remote control so I am using univarsel TV remote for this. Once while using remote may be I had pressed 2 or 3 buttons atonce.And it lost the colours.It seems that the colour system has been changed.The coloer working bar is moving up and down but there is no any colours.I had changed so many remots.All remots are working every thing but the problem is that no any remote have the MENU button and no any INPUT COD is replasing any button into MENU button so I change the vedio system.I had downloded 5 saprate files of its EEPROM[SDA2546] but no one is working. 2of them changed the aduio system and 3 of them changed the language and all 5 of them dont recover the colours. PLEASE HELP ME.Or menstion me to a univarsel remote having or working the MENU button.                            ITS SYSTEM IC NO[SDA20561-A015]     [MAY GOD BLESS YOU THE REALITY OF FATHE ON HIM]

Hi Ajaz,

You need the original remote and the service code in order to solve the problem. I suggest that you post your question into the eserviceinfo.com forum to see if anyone have this kind of original data.



I am bholanath
sir,a problam onida tv no red colour? (onida smart14/20/21)chroma IC no.M52771ASP Colour control hi to majanta colour. colour control lo B/W picture ok.RGB out put volt,ok.RGB VIDEO OUT PUT SECTION ALL OK.
Please halp me.THANKS

I suggest that you compare the voltage/signal in the crt board. look for the R,G,B pins and if there is difference in the voltage/signal then you know where to troubleshoot and if all the voltages/signals are good then the problem is in the picture tube.



HI Gasant,

My questions are.

1)      What drives switch mode power supply  transformers AC or DC currents. (I am under the impression that AC current drives them).

The transformer will get the 300 DC volt from the bridge rectifier and apply to the transformer primary winding. Next we have the power FET that can turn on/off by a signal generated by the oscillator ic (PWM IC).  When the FET is turn on, ac current will be stored in the primary winding and when the fet is turned off the stored ac current will be transferred to the secondary side and appear as DC voltage after it has gone through the secondary diode.

2)      The function of SMPST is to convert high volts to low volts or vice versa.

It can convert to high or low voltage and is depends on the secondary windings. The secondary voltages is determine by the number of winding loops. The higher the loop turns the higher will be the voltage.

3)      Bridge rectifiers convert AC to DC.

Yes you are right.



Repairing power supplies.

One other question,  I am looking for an oscilloscope.  There are many available,  analog, digitial, various ranges, pc based, etc.  can u recommend what would be the best suited for , or what specs should I look for.


Hi Terry,

I have a client that have bought the below scope and he found it to be very good:


Getting a 100mhz scope so that you do not need to upgrade again.




Since you didn’t sell the leakseeker 82 anymore can i ask you how good is this instrument

cause in your e-book you did mention about it .

This meter is good if you repair a board that have lots of components ex computer motherboard.

Let said if the supply line 5V missing how can i use this leakseeker to troubleshoot it as i know after wrong pad i probe i need to reset it again , is it .

5 volt missing can be due to power supply or voltage regulator problem. This meter is meant to check on any supply rail line that have shorted components. Ex if a board 5 volt line have 30 non polar ceramic cap (ex-0.1uf 50 v) connected between the 5 volt line and the ground and one of them have shorted, this could cause the 5 volt line to drop or the whole power supply will not work. By using this meter you can trace the fault out but then again it is not easy to use and you may need a schematic diagram of the board for fast troubleshooting.




I have a nice problem for you i have been given a philips23pf9956/79 tv/
And the problem is that after 5minutes centre of the top of the screen
Starts to flicker only in the centre then after a few seconds their is a 2″
black line
From top to bottom then after a few seconds the black bar changes and colour
lines running down

When you switch off and wait 10 minutes it is back to normal then starts

Have you come across this fault before


Hi Eric,

Thanks and same to you and family.  In your case, i suggest that you check on all the filter cap in the power supply section especially the secondary side. Make sure no dry joints in the power supply and vertical section.



i have a question about the anode cap. Do you know the name of the grease that can be found under the cap to prevent the hissing sound or is there any grease i can use? Thanks

Try this link:





Dear sir,
Firstly i want to wish u a Happy New Year 2012. My work is going fine. thinking yours also fine. I have some problem in my hp 1020 leaser printer. Printer does not power on even the switch is good and i have check all the cables printer switch. Can u give a suggesation for reparing the power board. I would be glad.
Thank your

Your sincerly

HI Sumit,

Printer no power- any output voltages from the smps? If yes then the mainboad could have problem. If no then you may need to check all the components in the power supply side.



Hi Tana,

I just followed the way I took it out. I have photos to help me. Anyway Thank you. I am working on another one View Sonic VX2423w . Everything on the power supply Board is good except the power fet. P10nkz70fp.
I am not able to source it . Can I use P10NK80zfp? .

Yes you can

Can I buy it  from your shop?

Sorry i do not have this part and my shop do not sell parts.

Jestine I have a Question. Correct me if I am wrong. When you connect the power cable and switch on, the smp Fet will be working assuming everything on board is ok. Will the secondary diodes  have voltage. Will The swp ic  get its  Vcc.

The start circuit  will only send power to the inverter IC after  the main board has sent the on signal. For the main Board to send the on signal the main board should  already be  getting its power supply.

The moment you plug in the power cable the output must have atleast one output to power the mainboard MCU. MCU got to have voltage in order to “think” by sending necessary signal to trigger the start circuit.

On what conditions will the power fet  not work.

No signal from the power ic, fet itself bad, shorted primary winding, shorted components in the secondary side and no supply to power ic.




I have been receiving your emails for some time now.  Now, I have the opportunity to test your knowledge because I have a problem.  If I can solve it, then I need not throw my spolit fan.  The problem is this – I switch on my fan and it automatically turns off either using the remote or manually.  I know a resistor is faulty but I do not know which is it.

What is your advice?



Hi Elan,

I have seen a ceiling fan board before and it does not consist lots of electronic components. I suggest that you remove the board and just check all the passive components and hope you could locate the bad resistor.


Hi Jestineyong the moment i switch it on  it goes to standby


HI Thami,

Have you check the dc supply to the main power supply power ic? Certain power supply use optoisolator ic and the cpu will send a signal to the optoisolator ic either when the remote control is pressed or the tv front power button is pressed in order to fully turn on the main power supply. If there is a missing signal or the cpu is bad then check the optoisolator ic area or replace the cpu.



Have problem:  I have 12 v and the current very low

The Process:does not work at first After you’ve checked sivich mode transformer input MOSFET, smd transistor and diodes short-circuited.I changed them all short circuit material.now, although it should be 24 volts, ı get 12v and very low current.I checked the robust 24 volt mosfet.have integrated circuit but ı can not test What can I do and different faults in my hand that I have 3 more.I hope I can repair.

HI Cihan,

Did you check all the components in the primary side. A low ohm resistor that increases in ohm could cause the output voltage to go low. Typical value for the low ohm resistor are 0.1, 0.22, 0.27, 0.33, 0.47 and etc. If your meter can’t test such a low ohm then directly replace and retest the power supply.



HI Max,
it was a pleasure getting a respond fron you since then i have purchase your book and download and i must say its awesome book i am totally enjoying all the information there is, great job putting all that needed information togather your are a blessing to the world of electronics.


if you don’t mind me asking say your SMPS goes bad what is your sequence of trouble shooting, meaning were do you start first and what are the most common component to go bad first and perhaps in what order if such. i greatly anticipate your quick response, thanks again.

It depends on what is the complaint. if totally no power i will check on the fuse, filter cap voltage and power ic supply voltage. If the complaint is low power, shutdown and too high voltage then i will check on the e-caps for high esr value, resistors and even transistor.



One thing is the other ATX power supply is have a shorted brigde rectifier can i replace it with four diode?

Yes you can replace with four 1N5408 diode.



2 More great articles, thanks.  Quick question, when your troubleshooting, do you have access to schematics for the devices your working on?  I have tried troubleshooting many things without schematics and it proves very difficult.

HI William,

No not really unless if there are components burn or you really do not understand how a particular circuit work.



H George,

Sir jestine, I have 3 units of defective CRT monitor office gave it to me. when i came home i try it to test using the light bulb tricks,and the 3 have different results the one is totally bright, the other is blinking slowly, and the last one is blinking fast. is it okay to test the CRT monitor even if it is not plug in to the CPU? also is it okay to diagnose it like troubleshooting TV?

The best is to plug into the computer as some monitor will not function properly without the computer.

i do some isolation technique like removing the center pin of HOT, removing the Horizontal and vertical connector but the short is not remove until i remove the degaussing coil then the light off. do you think what i’m doing is right? what i mean is my isolation technique is right?

It depends on the problem and degaussing rarely have problem. If the posistor is shorted the mainfuse will blow. I suggest that you follow the link below to isolate the problem:


Have a good day!



HI Victor,


1. with analog meter,how is the continuity of the lcd monitor power transformer,optoisolator,power ic and inverter transformers tested?

For transformer you need a Blue Ring Tester to test it. Testing optoisolator is already mentioned in the testing electronic components ebook.



2.if the power mosfet is burnt,cracked or shorted,does it affect the power ic and which other components are likely affected?

Yes most likely it will affect other components as well.


3. what is the work of the two or three schotty diodes found at the secondary side of lcd monitor power circuit?

To convert AC to DC.


4. what is the work of optoisolators in lcd monitors?

As a feedback for regulation purpose.


5. how is the str transistor-the power transistor with five legs tested for continuity with multimeter?

It can’t be tested with meter. You need to direct replace and retest.


6.  how can i know if lcd monitor power circit is 12v,19v,24v or what are the various voltages of lcd monitor power circuits?

You can know by performing the onboard voltage test. Common voltages are 5v, 12, and 14 volt.


7. can optoisolators,bridge rectifier and schotty diodes be replaced with any one seen whether same number or difference of numbers?

Yes three of the devices can be replaced with other type of part numbers.


8. what can i do if the circuit is working but the led light doesnt flash?

If power supply working and the power led does not light then the problem is in the MCU.


9. what can prompt one to search for schmatic diagram?

If there are components burnt or if you do not know how a particular circuit work.

10. since i am specialising in repairing lcd monitors,please list for me the type of components i should have in stock in my workshop for repairs which are commonly fail in lcd monitors?

fuse, bridge rectifier, big filter cap, power fet, secondary side filter capacitor, schottky diode and pico fuse.

11. is it adviceable for one to condemn lcd monitor power board becos of fault or when do you think one can condemn the board and go for replacement or modification?

If it has been strike by lightning or too many components burnt beyond recognition and no spare parts/schematic available.



Hello Jestine,

I was bought you book “Troubleshooting & Repairing Switch Mode Power Supplies” and want ask one question.
I want ask you about “Resistance Test Method” in pages 168-170. I can’t understand how testing equipment with this method. I understand that this test need to do with load (when testing monitor with main board). But what yuo mean when say that “if any the output voltage lines shows two same reading (low ohms readout), then suspect that there is a problem in that output line”? You mean that all voltage lines ohm reading must be separate?

Thanks for answer

HI Irmantas.

Thanks for the email. Let say the power supply have 4 output voltages which mean it has 4 lines to power up 4 different circuits-correct? This also mean that there are 4 output diodes. Now place your probes one to the cathode side and the other one to ground and test it one by one. A good  output line should have few hundreds to thousands of ohm whereelse low ohms mean there could be a problem in that output lines.



Hi Mr. Yong.


Last time I wrote I was about to order a new transformer to replace the defective one. The new transformer finally arrived, I replaced it and the backlights has come back to life. In other words, now the TV is working (as expected). FINALLY!

This has been a very, very long journey toward a successful repair. But, without you, I’m not sure I could have reach this final goal. Many, many thanks for your help and time toward this long quest. Also, thanks for your knowledge. Now, I know a little more about troubleshooting this type of problem and I also know a little bit more about transistor, regulator and transformer.

Again, many thanks.