1988 27 inch Sony Trinitron, rescued from the trash. - Page 2 - Videokarma.org TV - Video

radiotvnut · #16 10-25-2007, 03:36 PM

Just to be safe, the tuner is the can that should have a coax cable running from it to the antenna connector on the rear of the set. The IF can should be right behind the tuner.

MRX37 · #17 10-26-2007, 12:48 AM

Okay here's an update:

I resoldered the degaussing thermistor, and the thing's been degaussing fine. The picture looks MUCH better now! Here's a snapshot I took of it. Compare it with the last snapshot I took of the screen.

Now, I still have two other gremlins that need fixing.

Gremlin 1 is the tuner. I still haven't fixed that. Inside the two metal cans that Andy pointed out, one has a couple adjustable coils, and the larger one has about 50 or so copper coils!

The second gremlin is audio related. I noticed the bass is crackling badly. I checked one of the speakers and was RELIEVED to see that the foam surround had almost completely rotted away. The reason I was relieved, is that I can replace the speakers easy. If the crackling was due to an audio chip, I'd be screwed.

The second gremlin I can take care of. It's the tuner that I still need help on. Am I on the right track thinking it's the larger of the two IF can's that Andy pointed out?

radiotvnut · #18 10-26-2007, 12:55 AM

The one with the adjustable coils is what I'm thinkng of. These coils should be in a tiny, square metal can with the adjustment slug on top.

andy · #19 10-26-2007, 01:58 AM

Don't touch the tuner if you can help it. While I have seen them fail, they are usuallly very reliable. The IF coils are the common problem. Re-solder all the can coils and any obviously bad connections. Sony used that tuner/IF combination for years, so if you do need to replace one, it won't be hard to find.

MRX37 · #20 10-26-2007, 10:35 AM

Okay, so I definately want the smaller IF can with the adjustable coil's in it.

I'll go through it with a magnifying glass later today.

Oh yes. I also want to thank you all for your replies and helping me track down these gremlins. If you hadn't helped, I would have given up on this TV.

andy · #21 10-26-2007, 11:13 AM

I just noticed that it appears to be a two tuner model. The tuner/IF on that board is probably for the picture in picture. The main tuner appears to be on the main board circled. My advice is still the same. The IF can should be the same as the first one.

While you have the main board out, you should resolder the horizontal drive transformer. It's a small transformer that connects to the B of the horizontal output transistor. This is a large transistor near the flyback. Bad soldering here started to become very common around the time this set was made. If it's bad it will cause the HOT to fail and it may take the power supply with it.

What model is this set?

MRX37 · #22 10-26-2007, 12:13 PM

The model of this TV is: KV-27TX20

EDIT: Okay here's an update:

I believe the IF can on the side board is indeed for the PIP tuner. I removed it, resoldered all the coils inside it, and lo and behold, I get channels in the PIP window. Still nothing on the main screen.

I noticed a VERY similar looking IF can on the main board, and now I know what Andy was getting at. I'll desolder it and examine it.

radiotvnut · #23 10-26-2007, 02:48 PM

I'll second the opinion that the horizontal drive transformer needs to be re-soldered just to be safe. This was a BIG PROBLEM on '90's era Sony's. The loose connections short the HOT which shorts two transistors in the power supply and burns open a resistor.

MRX37 · #24 10-26-2007, 02:58 PM

I didn't see any suspect connections on the main board. All in all the soldering looks very good.

I think if it was going to fail due to bad soldering, it would have done it long ago.

I removed the tuner IF can on the mainboard and resoldered all the coils inside it, and resoldered it back to the board. No change.

I started playing with the AFT coil, and I ALMOST get a picture! Not quite though.

andy · #25 10-26-2007, 05:32 PM

You might be able to swap the PIP and main IF can. There's a slight chance that the PIP IF will lack an audio ouput, but chances are it's the same. The AFT coil is a common one to have bad soldering, so double check it specifically. I've managed to re-solder every connection in there except the bad one.

MRX37 · #26 10-26-2007, 09:14 PM

I'm putting it aside for now. This thing's a tedious nightmare to work on. I might get back to it at a later date. Right now I'm so frustrated with it that I'm almost ready to rip my hair out.

What I'll probably end up doing is desoldering the tuner IF can again, desolder the AFT coil and examine it for any damage, then solder it back in.

Then I get to go through the process of getting the main IF can back onto the board which is a pain in the ass because it doesn't like to fit.

Tom_Ryan · #27 10-27-2007, 12:44 AM

Post some pics when you get a clearer picture. Looks like you got a winner!

MRX37 · #28 10-27-2007, 03:54 PM

Quote:

Originally Posted by Tom_Ryan

Post some pics when you get a clearer picture. Looks like you got a winner!

The last pic I posted of it is a pretty clear picture of the browser menu on my Playstation 2.

Keep in mind that I am using a digital camera from 2001, and that taking screenshots of a CRT is difficult to do right.

MRX37 · #29 10-28-2007, 12:31 AM

All right, here's another update:

Removed the tuner IF can from the main board yet again. Checked all the coils for bad solder connections and could find none. Put the tuner IF can back onto the mainboard and soldered it into place.

I messed with the AFT coil until I got stable audio. then I got curious and tried one of the other coils and BINGO! Got a picture! That's not the end of it though...

After hooking the TV to cable and testing every channel, I turned the TV off and unplugged it. I left it that way until it had cooled off, then plugged it back in and turned it on. The picture was messed up again. I let it sit there and warm up, but the picture didn't come back, so I started adjusting the coils again.

I got it to a state where it would have a clear picture, then wavy lines appeared and grew more prominent until the picture went out. The picture would come back a split second after going out and be nice and clear, then the wavy lines came back and grew more prominent again until the picture went out again. It did this over and over, on every chennel I tried.

So I turned it off and unplugged it again, and left it sit for 10 minutes or so, then plugged it in and tried it again. Again, no picture.

I am starting to seriously suspect that there is something else wrong, and whatever it is, it's affecting the tuner.

Kiwick · #30 10-28-2007, 04:56 PM

80s and 90s Sonys often have bad capacitors, so replace each and every electrolytic cap around the IF.

I really hate the kind of "racetrack shaped" speakers they used in this set, they sound like lifeless crap right from the start, and after a few years their foam surrounds start to desintegrate... i wonder why they didn't use a rubber, cloth or paper surround instead...

Its no wonder this exact kind of speakers are used in modern all-crap sets... but it's really disappointing to find them in an expensive, otherwise nice 80s set...