Sony Trinitron TV KV-20V80

Post by **The Robman** » Tue Jun 12, 2007 5:44 pm

So, I found this set on the curb earlier today, so I just had to pick it up to see what's wrong with it. Well, it appears that there's no picture (there is sound) and when you turn the unit off, there's two dots on the screen, one green and one red.

Anything I should check before I kick it back to the curb that might be easy to fix?

zaphod7501 · Post by **zaphod7501** » Tue Jun 12, 2007 10:12 pm

That's one of their "One-Chip" sets. A master processor controls every function in the set.

The most common general failure is a poorly soldered vertical output IC. Usually a 7 pin on a heat sink. TDAxxxx is the most common type. Tapping the heatsink might cause it to pop back in if this is the problem.

A weak picture tube can do it also. Turning up the G2 control can sometimes bring it out of blanking. The G2 is either on the high voltage transformer below the focus control or on the CRT socket board (use an insulated screwdriver).

Anything else is going to be really hard to fix.

edit: I checked here before I saw your email

Post by **The Robman** » Fri Jun 15, 2007 1:47 pm

I found and re-soldered the "TDA" chip, but it didn't make a difference. So I looked for the control below the FOCUS control, which is labelled "Screen" and turned it. Turning this to maximum makes the screen turn purple (with lines across it). Does that give any clues as to what's really wrong?

zaphod7501 · Post by **zaphod7501** » Fri Jun 15, 2007 5:59 pm

That tells us that it has high voltage and filaments. The power supply is working and the micro is running and the CRT is probably OK.

It could be loss of vertical. Turning up the screen would cause the beam to bounce off of the inside of the tube, and produce brightness (but no video) on the screen. That's hard to tell for sure without seeing the lit screen.

It could be a failure anywhere in the video processing circuitry. (I assume you changed the video input to verify that it wasn't just a bum tuner).

Either way, it's scope and schematic time.

Sorry, but it may be back to the landfill time for this one, unless you want to start some serious troubleshooting. If you had a few chassis to borrow parts from it might be possible but I don't think we're in the "easy fix" category.

Post by **The Robman** » Fri Jun 15, 2007 7:06 pm

zaphod7501 wrote:It could be a failure anywhere in the video processing circuitry. (I assume you changed the video input to verify that it wasn't just a bum tuner).

I have something hooked up to the line input, but changing from line to tuner doesn't change the picture. In tuner mode you can hear the white noise that verifies that I don't have an antenna or cable hooked up, but there's no visual white noise.

Thanks for your help Steve, I guess this one's going back to the curb!

thedogzeus · Post by **thedogzeus** » Tue Jul 31, 2007 3:35 am

Rob, have you dumped this yet, if not I might just be able to help you fix....

Post by **The Robman** » Tue Jul 31, 2007 6:39 am

Nah, this set went back to the curb. What would you have suggested to fix it, I'm curious.

I have another Sony TV with problems...
http://www.hifi-remote.com/forums/viewtopic.php?t=5111

thedogzeus · Post by **thedogzeus** » Tue Jul 31, 2007 9:24 pm

Bummer, I reckon the other lads were pretty well on the mark with their diagnosis.

My money would have definitely been on the Vertical Output IC. IC541 on the main PCB (it's a TDA8172), worth about $5. If the fault was in the horizontal stage it wouldn't be coming out of standby, and if it was in the vertical sync stage it would have been shutting down after a few seconds.

No pix but sound OK 8 times out of 10 = V.OUT IC failure
Would have been worth a shot, but oh well.....maybe next time.

As for the 29", you still having audio problems? Has it got audio on AV/Monitor out?

Post by **The Robman** » Thu Aug 02, 2007 7:47 pm

The 29" doesn't have a video out, just an audio out.

The 29" works OK while it's just hooked up to a DVD player or something like that, but when I hook it up to the output from my FM modulator, the picture will eventually start to roll.

After I first got the set, I had it hooked up for several months and it worked fine, but then the trouble started. Steve tried helping me fix it and I even eventually took it to a TV shop, but the TV guy couldn't get it to start rolling again. Then 5 minutes after I bought it home and hooked it up again, it started rolling.

thedogzeus · Post by **thedogzeus** » Tue Aug 07, 2007 4:44 am

Leave it with me for a while....I'm on leave from work for a week or so due to birth of second bubby.

When I get back on deck I'l do a litle research for you and see what I can come up with.