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COlt Hero



Joined: 22 Aug 2010
Posts: 12
Location: USA

PostPosted: Sun Aug 22, 2010 11:07 pm    Post subject: JVC AV-2774S Shrunk Picture Reply with quote

Bought this set new in 1995 ($450). About a year or so ago it developed a tuning issue where it would not always tune stations in the cable tier of about 48-58. Sometimes the picture would come in OK, but most times it was covered with static-y lines and noise. To watch these stations I would usually switch to the VCR tuner. I learned to live with this problem.

But recently one night, while watching a program with no electrical storms occuring, the picture suddenly shrunk. I was hoping it was a bad analog amp on the cable TV side at the street, but when the cable guy saw the picture, he was sure it was the TV (plus I had another analog set that was OK). I think it's shrinking from the top edge because faces are being distorted/compressed. It MAY also be shrinking a bit on the left and right edges, I'm not sure. I pulled out the main PWB and flipped it over to find quite a few brown stains around several solder joints and brown smearing across the white "roadways" (for lack of a better term). I took several pictures which I could attach (if I can figure out how to do it).

Is this TV repairable? It's almost watchable the way it is, but the picture is a little too dark. Plus the bottom line is unreadable, so I haven't been using it.
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JTS1957



Joined: 21 Jan 2009
Posts: 2343
Location: Far, Far Away

PostPosted: Mon Aug 23, 2010 9:01 am    Post subject: Reply with quote

Turn up the screen control and check electrolytic capacitors in the vertical circuit.
COlt Hero



Joined: 22 Aug 2010
Posts: 12
Location: USA

PostPosted: Mon Aug 23, 2010 9:24 am    Post subject: Reply with quote

This is new territory for me. I've taken engines apart and written software, but never messed with circuit boards.

How do I "turn up the screen control"? Are you talking about brightness, contrast, that type of thing, or is it something in the service menu??

Are "electrolytic capacitors" listed in the service manual as 'E CAP', 'BP E CAP', and/or something else?

The service manual shows a block diagram with "V LIN", "V CENTER", "V HEIGHT" in the upper right quadrant of the Main PWB. Is this where I should be looking ... and what should I be looking for on these capacitors - distortion ?? leakage ?? bulging tops ?? And if I see this, does it necessarily mean the CAP is bad, or do I need to perform some test that I cannot likely perform? All I have is a digital volt meter...
JTS1957



Joined: 21 Jan 2009
Posts: 2343
Location: Far, Far Away

PostPosted: Mon Aug 23, 2010 10:13 am    Post subject: Reply with quote

Screen control is on Flyback. Try C426 100ufd/35volt - just swap 'em, they're cheap.
COlt Hero



Joined: 22 Aug 2010
Posts: 12
Location: USA

PostPosted: Mon Aug 23, 2010 1:01 pm    Post subject: Reply with quote

Follow up Q's:

1.) In the Service Manual, that CAP shows an "M" in the last column (as opposed to "J", "K", or "H"). What does the "M" stand for?

2.) CAP 426 is listed as a "safety" item. Should I be watching out for other CAPs with similar names that I should NOT be using??

3.) Haven't used my soldering iron and solder roll in a while. The last thing I remember doing with it might've been in the Toaster Oven (or maybe soldering on a new plug that my kids ripped off one of their "toys" - even after I warned them NOT to pull on the cable in place of the plug!!!). No - wait - I "soldered" a plastic box fan blade back together with it. Boy, did that stink up the kitchen! And it was a weird problem, too! I came home to find the blade sitting inside the cage of the box fan, perfectly detached and not a scratch anywhere. It was like it just fell off on its own - taking a good portion of the center hub with it!!! The fan would even run without it, but not without bobbing up and down and falling over !!!

Anyway, the iron is a "pencil" style from Radio Shack. I think the barrel on it is about 1/8". Don't know how many watts offhand. How do I know if it'll be too hot for this job and what gauge and type of solder should I be using?
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JTS1957



Joined: 21 Jan 2009
Posts: 2343
Location: Far, Far Away

PostPosted: Mon Aug 23, 2010 2:01 pm    Post subject: Reply with quote

1) page #15 & 16
2) 100ufd 35 to 50 volt 85-125 degree C @ what ever % tolerence you can afford
3) Clean/re-tin iron, should work fine. I use a broken iron that the barrel glows cherry red in the dark. You can put your finger in the flame of a BIC lighter, it's only when you KEEP your finger there that you get burned.
COlt Hero



Joined: 22 Aug 2010
Posts: 12
Location: USA

PostPosted: Mon Aug 23, 2010 7:27 pm    Post subject: Reply with quote

1.) The manual shows the "type" descriptions (BP, FT, etc.) and some are missing - but, interestingly, it doesn't show 426's which is E CAP (electrolytic). I don't see where it makes any mention of what those single letters are in the right-most column (M,J,H,K,F, etc.) under the capacitor section. It shows "M" and "K" for resistors (Mega and Kilo), but not for the capacitors.

My iron is a 30-Watt. The solder is Rosin Core (.050), 63% tin, 37% lead.

Would these be OK? The heat reference I made was in regards to the possibility that the iron might be too strong and damage the board.


Last edited by COlt Hero on Mon Aug 23, 2010 7:43 pm; edited 1 time in total
JTS1957



Joined: 21 Jan 2009
Posts: 2343
Location: Far, Far Away

PostPosted: Mon Aug 23, 2010 7:31 pm    Post subject: Reply with quote

Fine by me. Cool
COlt Hero



Joined: 22 Aug 2010
Posts: 12
Location: USA

PostPosted: Mon Aug 23, 2010 7:44 pm    Post subject: Reply with quote

That's funny. I was editing my post while you were responding you my unedited post ...
JTS1957



Joined: 21 Jan 2009
Posts: 2343
Location: Far, Far Away

PostPosted: Mon Aug 23, 2010 8:13 pm    Post subject: Reply with quote

Tolerance.
Are you looking at the correct page 15/16?
WRONG: bottom right= Sep. 1993 No. 50832
CORRECT: bottom right= (No. 50832)
Right before start of exploded views parts list!
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