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Electronic Repair Questions/Answers And Testimonial- Part 22

By on November 16, 2008


Yes I did get it nice job. Me & my team agree you are just Awesome!!!!! I told you about a problem & unlike most people who would have just pushed there product. You instead directed to a site with a lot of free information. That shows great integrity. Please understand I hold you in the highest of respect. I will be going over to a friends a bit latter. He wants to or may all have bought your e-book for me the only concern he had was the money back it showed that Citi will only refund defective products but your site say 100% guarantee. Of course my gut tell me we will not need it any way. I’m quite sure it a power or ground problem cause took the second fan out & tested it & it works the all diodes work as well when I test them just not on the circuit board. In any case I thank you for your insight & help keep up the great attitude and work.





Hi M,

One more clarification is P7NK80ZFP is zener protected device internally,will it effect for external circuit.

As far as i know of using substitution number, there is no effect.

Can we use higher voltage and current rating i.e.P7N90C  900V, 7.5A in place of FQP7N80C (800V,6.6A).Because FQP7N80C is not available at present in the market.

Yes you may use a higher voltage and current.


Dear Mr. Yong,I bought your EBook + bonus books, thanks very much for
distributing knowledge among us,we enhance our knowledge by reading your
books,it is written in simple English language which even a child can






Jestine Yong

if you can answer then plz reply me

what is the difference between a normal speaker,piezo buzzer and horn speakers


Hi Sharan,

Check out this page as it has a long explanation :

and horn speaker at

Hope this helps!




I’m working on a RCA CTC 187 Chassis the problem is, this set initially had a shorted H.O.T. I replaced bad output xsistor. The unit powered on. This worked with the xsistor in, but the transistor gets hot.The regulator i had to replace after checking, and finding collector voltage was @ 210 volts dc after replacing the regulator i measured 167 (should measure 145 volts dc to hot ground) volts @ the regulator output now i understand the set is not on  when making these measurements. The H.O.T. voltage should be approx. 145 volts dc.


This is a 31″ set. The 145 volts is running when the set is in standby, but whenever, i measure the voltage at the regulator the H.O.T  voltage jumps up to 210 voltage from cold ground.I replaced primary side diode, ( this feeds 145 volts to the fly back i also removed the pin that feeds the H.O.T from  xformer) capacitors, and resistor 33k ohms to ground at the cathode side of the diode.


If the B+ voltage too high it would kill the HOT slowly or instantly. If you see other voltages increases too then suspect power supply problem. If this set use optoisolator then check on this circuit area.

Visit this link as it has information on how to isolate the problem at

Best regards,



Hi B,

 Here is your questions and answers:


 I’ve eventually solved the smps problem after struggling for about one week. The culprit was the leaky power transistor 13007 in primary circuit. But it is worth the effort because it helped me to know the real power of the ring tester.

Congrat on your repair.

Your suggestion to remove all of the big transformer and use analog meter set to x 10 k to check on all of the secondary side output diode, I haven’t done it because I have scanned through all the secondary diodes and all are OK. But I am very curious to know why should we remove the big transformer first before checking the secondary diodes as removing all the transformers is quite an effort to do it, I’d like to know your logic thinking about this.

This way i don’t need to solder out secondary diode and i can straight test the diodes on board with accuracy too.

After downloading some ATX smps schematic, I have problems to identity where is the primary of the transformer, even after reading your blog about identifying transformer or inductor. Some are obvious to know it, but some are not because it seems to have more than one primary ( primary A & B ). Here are some of my questions about this.
1. Is it true that the winding drawn on the left side of the core in the schematic is always the primary winding?
Most of it yes!

2. Could the inductor and transformer all be wound together in one entity, so it is a mixed form of inductor and transformer?

No, its all independent

3. Is it always true that the primary side has fewer pins and has higher resistance than the secondary side?


4. Could it be that the two pins of a winding is crossing the core ( face to face ) instead of
side by side

Yes it is crossing the core but separated by an insulation tape

5. Where can I find in the internet the various lead pinout of those many kinds of smps transformer?

I guess you find it from monitor/tv schematic diagram which is much easier.

About the isolation transformer that I’ve built myself, your suggestion  is to power the device  under repair and the oscilloscope from the ouput ( two pins ) of the isolation transformer, but the manual of my digital storage Oscilloscope says it requires to connect the protective grounding conductor of the AC power to an earth ground. Which should I follow?

Infact yes you can connect the digital scope to ground because the output from the isolation transformer already has no connection with the ground. As for me i like to connect both

Best Regards,
Jestine Yong



Mr,Jestine Yong

                          i am very thanks full to you that pdf file you send me. i read these files it is very very easy and helping for me. i hope full next week i buy ur e-book because i need it. this time i want a help i repairing a lcd but problem in this lcd when i do power on of lcd display will ok but after few second screen will be white. pls tell me what & where problem in lcd. pls u can send me pdf file whit diagram. thanks,


Hi F.W,

After sometimes turn into white display suggest that it could be dry joints problem, bad e-caps at secondary side or even a bad lcd panel.



I am trying (right now) to figure out an issue with a Princeton VL1919 LCD monitor.  “No input signal…going to sleep” is the message on the screen.  I replaced all the caps and thought it was the issue.

On Nov 10, 2008, at 7:44 PM, Jestine Yong wrote:


Hi R,

Thanks for recommending your friend-appreciated that. As for your Monitor, have you check the connection between the vga connector and the mainboard. A loose horizontal or vertical signal wire could problem like that.



I am looking through the information I purchased from you on VGA connections or components.  I have a Princeton 19″ LCD that works with the white DVI connection but not the blue VGA connector.  All the caps on the graphics board look okay.  Is it possible to have only one section of the graphics board bad?  Meaning…the side with the VGA and not the area with the DVI?





Hi R,

Yes it is possible. Some LCD Monitor have the setting of which one you want to choose from the menu. Since you said the vga have problem, now try trace from the vga connector at the mainboard side and look for if there is any smd diode shorted or not. In fact you can compare the resistance between the 3 colors. Check the resistance to ground to between the 5 lines (RGB, H and V), It should not show any low ohms reading.

Hope this helps!



Gud Day sir..i repair a monitor AOC model 771s..and its so very hard for
me 2 fix it because i dnt knw what is the relly problem..the picture is
dark and its in the above of the scren,and i cannot adjust the menu..


Hi C,
Try check the vertical circuit and replace the vertical ic and retest again. Make sure all the output voltages at the secondary side of power supply is good. Hope this helps!



Hi Jestine,recently i hv  facing problem on Dell 17 LCD model:#1.E176(no power) n *2.E177(no display).just to get some ideals or clues;test point/voltage measurement or experience.Like to hear feedback ASAP.tq FYI for #checking status:fuse ok,primary got o/p but secondary no(suspect IC)           *checking status:secondary o/p got 4v n 14v,power LED in orange Rgds Hew


Hi Hew,

If the E176 does not have output and you have checked all of the primary side components (which include the secondary output diodes) then i guess you have to replace the power IC and retest again. Make sure the power IC is receiving a supply voltage of 10 to 20 VDC.

If all the output voltages is okay and you got orange light then this suggest a problem in the mainboard.  Please check the 4 volt line again as it should have 5 volt and you have to test it with a digital meter that have a better accuracy. In Samsung LCD, if the LED turned orange color it would be 100% the mainboard have problem. Hope this helps!



Hi Jestine,


Yes, my LCD monitor is back to normal again after replacing the transistor as what u told me. It’s great.


Thank you very much for your advice.


Best Regards




Hi S,

 Here is your questions and answers:

1)supply voltage to the power IC?
yes, in put voltage is ok ( AC)

It should be DC voltage to the supply pin of the power Ic. Please check the data sheet of the power ic.

2)Have you check whether secondary side have voltage or not?
No, not get any out put voltage.

If totally no output this suggest the problem in the primary side.

3)power LED is not ON .

If the power supply is not working the power LED would not On

you want photograph to you i will send to you.

If you have -yes you may send one for analysys.

if you possible we use the any other power supply & check the LCD ?

If you have the similar module of power supply, yes you can compare it.

But i not get the proper 0ut voltage for the Use back light & AD board.

No output from power supply means no output to backlight and ad board.

you pl send the this type power supply board out put i match the any other power supply for  the same.

Sorry i do not have such power supply in my workshop.




Hi B,

 Here is your questions and answers:


Recently I like to buy some common parts needed in future repairing, and about this HOT transistor I am not convinced whether it is genuine or not because this is the first time I bought a HOT transistor and never had experience repairing CRT monitor before, the price is about US$1. The reason I am not sure if it’s a genuine one is because in between the pins I saw plastic material remains and the surface where the marking written is a bit rough. Could I use the Peak Atlas DCA55 to confirm it? What is the analyze result from a good one? Which parameter is especially important from the DCA55 result. The hfe I got from the analysis is only 10. Please see the attached photo.

Hard to differentiate it from the outside or even with meter (peak analyzer) as sometimes there are manufacturers tends to change their HOT version. The best is to install in the Monitor/Tv and test it with full load (under operation) as this way one could tell if the HOT is good or bad assuming the equipment have no other problem other than HOT problem.



Hi M,

 Here is your questions and answers:

I am working on SMPS , which is  based on ML4800 PWM circuit.The problem we are facing is, No out put.For that we replaced  new MOSFETs and 0.2 Ohm resostor, which is connected to Bridge rectifier and  SOURCE & GATE of the MOSFET, K2843 and 7N90.DRAIN of the MOSFET K2843 is connected to 08TB60 Ultra fast recovery diode.0.2 ohm resistor is going to Child card i.e. PWM circuit.In PWM circuit 30 ohm resistor and Zener diode is becoming bad which is connected to pin 3( I sense) of ML4800  IC.

If we replaced good MOSFETs , 0.2 ohm resistor,30 ohm resistor and Zener diode(12V).Same is going bad again and again.I have done cold check for other components and found ok. Please suggest me how to go ahead and solve the problem.

Have you check the primary winding of the transformer with ring tester?  Sometimes a shorted components in one of the secondary side output could cause the power malfunction. If this power supply have an optoisolator then check this circuit and the optoisolator too.

Best regards,
Jestine Yong



Hi A,

Here are your questions and answers:

I just bought your book to help me with few problems I have here.

Thanks for the support!

One is a 17″ DELL monitor (have a BENQ DS1107A PCB) and I cannot find
the 1000uF capacitor you are referencing in your book.

The 1000uf cap is located at the secondary side of the power supply. It could also be different model that the manufacturer did not use the 1000uf capacitor .

The monitor will always turn on, but it keep shuting down the screen,
sometimes after fews seconds and sometimes after hours, but once it
start doing this it just won’t stay on. The power button stay on

This could suggest a problem with the backlight. A weak backlight always  cause such problem. First it was okay but after it gets hot the screen will shutdown.

My second problem is with a projector, Optoma EP-739 that will turn
off after about 5-10 minutes. I have already tried to bypass the
thermo-sensor but that made no difference.

For your information, i have never repair projector before. However from your description, this could be a dry joints problem or bad filter capacitor in the power supply.

The last is about two ViewSonic VE107b that I have fixed long ago and
now one of them is slow to turn on to full brightens

This could be the eeprom ic problem in the mainboard or even bad LCD panel (you can compare it with the other similar model you had)to find out where the fault is.

and the second
work fine for a while but sometimes it start changing colors, similar
as if the VGA connector is loose but it is not.

Try check for any loose connection cable between the mainboard to the lcd controller board. Sometimes a bad filter cap may also cause such problem.

At the moment I’m still trying to order a ESR to help checking the

This is the best meter and you should have one in your work place. Have a good day!

Best Regards,
Jestine Yong




Dear Jestine


I dont know if you can help but I have a problem with a JVC AV28GT1SJF TV. I think that its a 11AK45B5 Chassis. When switched on the led goes red then green and the power stays on for about 5 secs then the led goes red  then green for 5 seconds and keeps cycling. I can see the HT come up then shuts down repeatedly.


Im not sure if the child lock is activated and is causing this problem more likely that its shutting down because of some faulty component.


Secondary voltages cycle with the on off action.  Have you come across this type of problem?


Have a nice day.






Hi C.H.T,
I have a good article by sencore on how to find out if the problem is in the power supply or from the high voltage side. Please visit:

For your information, child lock would not cause the high voltage to come on and off. Most probably fault in the components.

Hope this helps!

Best regards,
Jestine Yong



Hello Jestine,
I just read your message to me.

I could’ve love to purchase your E-book but because Iam not financilly bouyant at the moment, I can’t do it now. but pls if you can, kindly assist me. I have a question; My television has a bright horizontal line across the screen. I understand that it can be caused by a vertical ic. But are there other things I can check that relates to that?…….please! THANK YOU.   

Hi I,

Yes, check the surrounding components near the vertical ic. Make sure the supply voltage to the vertical ic is good.

Hope this helps!



Do you know any good tutorials on how to use RF signal generator and function generator for TV repair/troubleshooting?

Thanks for your support!


Hi Billy,
Here is some useful information about test generator:

Hope this helps!

Best Regards,
Jestine Yong




Good day to you!
Thank you for this website, this can help to study more about electronic equipment.
and how to repair. agin thnak you and God bless!






  1. abualgassim

    November 19, 2008 at 7:25 pm

    Dear Mr jestine.
    I have been working in lg monitor 14 inch for more than amonth,and Idid not find the problem, every thing seem to me work fine. the power transistor 10N20c get hot very quickly and after some minutes become short and also the transistor STK630 GET hot,so I appreciate you if you could help to find the problem.

  2. admin

    November 19, 2008 at 9:20 pm

    Hi Abualgassim,

    Try check all the components in primary section especially the e-caps. Make sure also the components used are from the original part number.


  3. Luis Paradero

    February 5, 2009 at 12:18 pm

    Hi Jestine,
    I have an Optoma projector model EP732. One of the voltage regulator in the power supply module exploded. I have no idea what the part no. is. I've tried searching schematic diagrams in the internet but to no avail. Do you have any idea what could be the part no of this voltage regulator? Appreciate your help.....Thanks

  4. admin

    February 5, 2009 at 2:00 pm

    Hi Luis,

    Sorry i have no information on this projector.


  5. LCD TVS

    March 5, 2009 at 10:57 pm

    thanks, your article is very informative. : )

  6. joseph cuenca

    July 5, 2011 at 1:05 am

    hi jestine,
    i'm working on my aoc 771s monitor i cannot adjust the vertical display in the menu.i already change the stv9302a the one with 7 pins but still i cannot adjust the vertical in the menu what parts do i have to replace.
    thank's and more power!

  7. admin

    July 5, 2011 at 4:41 am

    HI Joseph,

    If all other functions can be adjusted then most likely the eeprom data may have corrupted.



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