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Another Zener Diode Tester Was Built

By Jestine Yong on September 9, 2013

Another Zener diode tester was built by one of my ERG members Mr Orin Fraser from Guyana. The zener diode tester diagram came as a bonus when you purchase the Troubleshooting And Repairing Switch Mode Power Supply Ebook. Check out the photos below:

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zener diode tester

8 Comments

Antonio

September 11, 2013 at 3:48 am

Hello Mr. Jestine Yong, I extend to you and any other person who can help me to resolve a fault on an old CRT TV MIVAR (Italian brand) which has this problem:
The screen looks green with white lines Retrace and no video image, while the audio is OK.
If you can kindly tell me in general at what stage should I turn my attention to repair the aforementioned 25-inch CRT television.
I thank in advance all those who will want to give me advice.
greetings
Antonio Simone
Italy

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- Jestine Yong
  
  September 11, 2013 at 11:11 am
  
  Hi Antonio,
  
  It can be shorted tube (green cathode shorted to grid) or it can be the green circuit have problem probably shorted transistor. Try compare the voltage/signal between the green and blue/red circuit. Any differences is the clue for you to trace the problem.
  
  Jestine
  
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castro luis

March 26, 2014 at 12:06 pm

goodnight sir jestine yong, advance my greetings, this is to ask a technical aid. I have a 32 inch LED TV is heard and not seen, I put a lamp behind the screen to see if the picture and gave me cash given image, but the LEDs are good, and the other probe pernden, could use to give me a no clue if incombenientes.
thank you very much., and I congratulate you for your contributions.
as I get the diagram diode tester.?

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- Jestine Yong
  
  March 26, 2014 at 6:05 pm
  
  HI Castro,
  
  If the power led is red this could mean the mainboard MCU/flash rom could have problem. As for the zener diode tester diagram, it is part of the bonus package for those who bought the SMPS repair ebook at http://www.PowerSupplyRepairGuide.com
  
  Jestine
  
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Kim

June 28, 2024 at 7:49 am

Hello, The great sir Jestine yong,In fact I have 29 inch LG CRT TV(CN-29H3) which won't display any screen.
and it is written "MC-7CA(MAIN) 6870VM0056C(6) 980424 L.W.G(0)" and
"MC-7CA(CPT) 6870VS0167A(1) 971014 K.J.B(0)" on the surface of its PCB.
By the way,I found a schematic of MC-7CA PCB and It seems that its HOT area is almost same to CN-29H3. So I upload it to below dropbox link.
https://www.dropbox.com/scl/fi/n1rdt7bio811ia8a70rg5/lg_chassis_mc-7ca_sch.pdf?rlkey=x089bay1dgeamve8gqvx0fst7&st=0vyekxzy&dl=0

I measured pin#9 of STR-S6707 by placing red probe of analog meter to pin#9 and placing black probe to negative termainal of C808 the biggest capacitor(400v 470uf) and It was measured 6.4-6.5Vdc.

But In the datasheet of STR-S6707,It says that its On-State Voltage is 7.6Vdc.So I think that there would be a defective component which is undoubtedly adjacent to pin#9 of STR-S6707.

And In the same way,I measured cathode of ZD808 zener diode and Q800(C3852A)base,It was measured 7Vdc.

I also measured positive terminal of C805 and cathode of D807 and Q800(C3852A)collector,It was measured 10.8Vdc.

Judging from pdf files(lg_chassis_mc-7ca_sch.pdf), ZD808 has 7.5V specification.
So I doubt that ZD808 zener diode have been defective.
and It is written B.75 on its surface.
But I cannot found any zener diode in the market which is written B.75 on its surface.
What zener diode should I purchase for replacing this 7.5v zener diode which is part of STR-S6707 circuit in the 29inch LG CRT TV(CN-29H3)?
Any reply would be very much appreciated.

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- Jestine Yong
  
  July 5, 2024 at 9:35 pm
  
  Hi Kim,
  
  You can get a 1N4737A zener diode that is rated as 1 watt 7.5 watt.
  
  Jestine
  
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  - KIM
    
    July 14, 2024 at 9:03 pm
    
    Hello, The great sir Jestine yong, Thank very much for reply.
    
    I replaced ZD808 zener diode with 1N4737A But it still won't display any screen.
    So I desoldered R831 which is connected to B+ solder joint of FBT and soldered 60w bulb,and I measured B+ filter capacitor and It was measured 120Vdc.
    
    So I think that there is no faulty in the HOT area. So I doubted maybe there was loose contact on the pin of IC,Beacuse This CRT TV was manufactured over 25 years,So solder joint would not as tight as twenty five years ago.
    
    And it seems that weight of its PCB is about 2kg,I think that Whenever I deposited this heavy PCB on the floor,this would put pressure on the pin of IC.So there would be minor crack on its solder joint.
    
    I soldered all pin of IC01(LG8708-08A), IC201(GL3812),IC501(TB1231N) and Turner TU101(TUSHB-A07A) at the bottom of PCB, and It finally displayed screen!
    
    Once again, I’m grateful for taking time out of your busy schedule to give me unrivalled expertise.
    
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    - Jestine Yong
      
      July 16, 2024 at 5:10 pm
      
      Hi Kim,
      
      Awesome and Congratulation!
      
      Jestine
      
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