Comments on: Another Zener Diode Tester Was Built

By: Jestine Yong

Jestine Yong — Tue, 16 Jul 2024 09:10:46 +0000

In reply to KIM.

Hi Kim,

Awesome and Congratulation!

Jestine

Likes(0)Dislikes(0)

By: KIM

KIM — Sun, 14 Jul 2024 13:03:13 +0000

In reply to Jestine Yong.

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.

Likes(0)Dislikes(0)

By: Jestine Yong

Jestine Yong — Fri, 05 Jul 2024 13:35:22 +0000

In reply to Kim.

Hi Kim,

You can get a 1N4737A zener diode that is rated as 1 watt 7.5 watt.

Jestine

Likes(1)Dislikes(0)

By: Kim

Kim — Thu, 27 Jun 2024 23:49:17 +0000

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.

Likes(0)Dislikes(0)

By: Jestine Yong

Jestine Yong — Wed, 26 Mar 2014 10:05:33 +0000

In reply to castro luis.

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

Likes(0)Dislikes(0)

By: castro luis

castro luis — Wed, 26 Mar 2014 04:06:33 +0000

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.?

Likes(0)Dislikes(0)

By: Jestine Yong

Jestine Yong — Wed, 11 Sep 2013 03:11:57 +0000

In reply to Antonio.

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

Likes(1)Dislikes(0)

By: Antonio

Antonio — Tue, 10 Sep 2013 19:48:46 +0000

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

Likes(0)Dislikes(0)