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#1
10-24-2007, 08:29 PM
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1988 27 inch Sony Trinitron, rescued from the trash.
It's not dead, but it has a couple gremlins, two that I know of so far.
The color purity is all screwed up, not sure yet if this is from magnets, or if the degaussing thermistor went. I can't tune in any channels. I almost get something on a strong channel, but it's like if you play with the fine tuning knobs on an older set. It seems like the tuner is out of alignment. The picture tube seems to be very bright. No idea how good the convergance is yet, but I can read the channel numbers fine. Tomorrow I will test it somemore, and take some pics of it. Hopefully somebody here has dealt with this before and can help me. 
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#2
10-24-2007, 09:23 PM
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I've seen similar problems on Sony's of this era. As far as the degaussing circuit goes; check the solder connections on the thermistor. I was given a 27" Sony once that simply needed it's degaussing thermistor resoldered.
The "tuner trouble" may be caused by a loose coil inside the IF can. The IF can is a small metal can located close to the tuner. It will have to be unsoldered from the chassis and the metal shield unsoldered to service it. Resolder all the little coils on that board.
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#3
10-24-2007, 09:57 PM
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Quote:
I also need to remove about 20 years of dust from its inside. I'll post some pics of it tomorrow.
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#4
10-24-2007, 10:49 PM
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Was the set "thrown" in the trash or gently "set" there?
If it was tossed the shadow mask could be damaged, no repair for that except a new CRT, but let's hope for the other options. If you have a Weller soldering gun they make a dandy degaussing coil, just power it up next to the screen and wave it in a circular motion while pulling it away, when you get far enough back that it's not affecting it anymore release the trigger.
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#5
10-25-2007, 01:41 AM
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Quote:
  reminds me of this year's new years find, 32" 1999 sony that needed the power supply/horiz out kit... works fine now....
__________________
 Nothing is ever completely fool proof, because fools are so ingenious.
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| Audiokarma |
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#6
10-25-2007, 10:06 AM
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If you can read the chnnel numbers fine, then convergence is fine. Also, I would definitely resolder the tuner and controller, sounds like this could be the tuning issue
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#7
10-25-2007, 11:22 AM
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Quote:
Also, I believe that Trinitrons don't use a shadow mask. They use the apeture grille design. In any case, the casing is undamaged, so I highly doubt anybody threw it.
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#8
10-25-2007, 01:05 PM
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The model of this TV is: KV-27TX20
Here's a couple pics. This one is of the back of the TV with the cover removed:  And this one is a better shot of that side board that is attached to the frame covering the back of the CRT:  The impression I get from this thing is that it was way overbuilt. This looks like a complex beast, and I swear that I think this thing has TWO flybacks in it! I think the tuner section is one, or maybe both of those larger metal boxes on the side circuit board...? I have no idea where the degaussing thermistor is.
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#9
10-25-2007, 01:13 PM
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I used to have a 1987 27" Sony Trinitron TV. Sony sets of that era were built to last and be serviceable. The degaussing thermistor will likely be a small black cube soldered to the main pc board near the power supply. The thermistor itself is inside the black plastic cube. If you are going to do any serious troubleshooting on this set, you will need the Sams. They are not impossible to work on but they are complex.
__________________
Just look at those channels whiz on by. - Fred Sanford
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#10
10-25-2007, 01:43 PM
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Here's a shot of it working in composite video mode. The screen is the browser on my playstation 2. As you can see, the colors aren't right.
 Seeing that it does indeed get a picture, I am more encouraged to fix it. Also, I turned it off and on and ACTUALLY got a local channel to come in! Turning it off and on again made it revert back to static, with some staticy audio, but it bolsters the loose RF coil theroy.
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| Audiokarma |
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#11
10-25-2007, 01:59 PM
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That looks like a damaged shadow mask/aperture grill to me. The aperture grill, which functions exactly the same as a shadow mask, must be in exactly the right position to work. The heavy metal frame that's needed to keep the drill wires under tension is very heavy and easy to knock out of position. A degaussing problem usually results in a pattern of concentric circles. It's easy to drop a set with enough force to move the shadow mask out of position and not damage the cabinet. Try unplugging the degaussing coil and manually degaussing it.
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#12
10-25-2007, 02:44 PM
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I have no manual degausser.
Never mind. It's DEFINATELY the degssing thermistor! I wiggled what I thought was it, turned the TV on, and BINGO! Perfect picture!! I'm still trying to determine where the tuner coils are. If anybody knows, I'd much appreciate the help. Quote:
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#13
10-25-2007, 03:28 PM
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I think the IF can is the smallest of the two cans on that side PC board. Actually, I've seen several Sony's with loose degaussing thermistors. They get so hot that, over time, the solder just breaks loose from the PC board. In fact, my mid '80's 19" Sony has gotten so I can see the degaussing action on the face of the CRT after it warms up. I'm sure that's the problem with mine. I just need to get off my lazy butt and fix it. I've seen the thermistors in the '90's RCA's get so hot that they just fall apart.
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