Fixing a Blown-Out Sony TV

Hi,

A 19" Sony from 1990 recently blew out. For the past year or so it has been flickering a bit, usually clearing up when warmed (I also had a little success by fiddling with the power cord, ie getting a better connection by readjusting the connector).

The other day while it was on, it began to smell like something was burning, and then the TV went off (I think there was a noise too). I cracked 'er open and took a look. I found that one of the three cement, fusible power resistors had literally blown. The ceramic housing was split down the middle of the length and the wire-wound resistor was cracked in half. (Oh, and both of the fuses that I could find were fine.)

As luck would have it, I happened to have an identical resistor that I salvaged from the circuit board of another TV from a few years ago. Like the dead one, it too was a 20W, 150 Ohm cement, so I replaced the dead resistor and hoped for the best.

Unfortunately it was only slightly better. Before, the relay would click, but nothing else would happen (no LED even). Now, when I plug it in and turn it on, the relay clicks, and there is a brief startup hum (but nothing else), and then it goes back to click-then-nothing at all (other than the new power resistor heating up). If I wait a while each time before turning it on, then it will do the brief hum after the relay click.

There is a 560uF, 200V capacitor nearby whose top is fairly bulged. Unfortunately my DMM doesn't have a capacitance testing function, but I figure my next move is to replace the cap.

Any ideas? Thanks.

--
Alec S.
news/alec->synetech/cjb/net
Reply to
Alec S.
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I don't hink the cap is your problem. A bulged or curved plastic cover on the top of the cap is not a failure. If it's the metal can that has split at the top (vented), fine.

We really need a model number to give you any more specific advice.

That said - the resistor you mention is not a typical Sony failure that I am aware of.

Mark Z.

Reply to
Mark Zacharias

Mark Zacharias wrote (in news:001b6257$0$19677$ snipped-for-privacy@news.astraweb.com):

I don?t think it has; when I press down on the plastic cover, it pops down without much resistance.

It?s a KV-20TS30.

I suppose not, but I was running on some general tips like in

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Thanks.

--
Alec S.
news/alec->synetech/cjb/net
Reply to
Alec S.

Hi.

What, if any, experience in electronics repair do you have?

Reply to
Meat Plow

In the words of McCoy, Star Trek (TOS): "It's dead, Jim" comes to mind.

It seems you do not know much about what you are doing, so I'd be somewhat worried that you may kill yourself. Do be careful.

Reply to
PeterD

It's not? Odd, virtually all caps I've run across with buldged cases were failed.

And a split case (the extreme, or final stage) is not 'fine'. It is dead.

Reply to
PeterD

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Normally speaking big electrolytic capacitors such as a 560uF, 200V has a plastic disc on top of the aluminium cylinder and I it=B4s quite frequent for that disc to become bulged, while underneath the aluminium can is perfectly flat, thus one can=B4t say that the cap is damaged just because that plastic disc became bulged. I don=B4t think the cap is damaged, and the description of the TV failure points toward something more serious: a damaged HOT, a shorted switching transistor, etc.

Reply to
lsmartino

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Oh, I am careful. I am quite aware of the remaining charge in a display as well as how to discharge it (=93shoving a grounded screwdriver up under the anode cap=94 lol) should the need arise (which it has not).

Reply to
Synetech

PeterD wrote in news: snipped-for-privacy@4ax.com:

if a electrolytic's ESR has climbed too much,it's a "failed cap",and if it's bulging,it's failing.

And if it's discolored badly,it's certainly suspect.

--
Jim Yanik
jyanik
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Reply to
Jim Yanik

I was talking about a plastic disc which is often seen on the top of larger, mostly older electrolytics. It is essentially an insulator to prevent one from touching the metal can of the capacitor. Often they become contracted or curved or even fall out altogether, but it has nothing to do with the "bulging" (venting) often referred to on the internet and which we see in newer, cheaper sets. Perhaps I should have been more clear.

When I said "fine" I was just in the mode of agreeing that the OP had a bad cap if the top was in fact vented. Once again I should have been more clear.

I have never seen Sony's suffer from the bulging cap scenario in their switch mode supplies, but of course it could happen. More often, if there is a regulation problem, the set just shuts down. In a typical bulging cap failure, a high ESR causes the regulation trouble, which runs the voltages higher, which accelerates the failure, and the caps vent.

Mark Z.

Reply to
Mark Zacharias

Oh, I am careful. I am quite aware of the remaining charge in a display as well as how to discharge it (?shoving a grounded screwdriver up under the anode cap? lol) should the need arise (which it has not).

Please don't be insulted, but anyone who describes a safety procedure as "shoving a grounded screwdriver..." and adds "LOL" should just discard the TV and purchase a new one. If you are lucky enough to repair the TV without injuring yourself, the TV may become a fire hazard if it is not repaired correctly.

Chances are the TV originally just had a bad solder joint. Moving the power cord flexed the circuit board and opened and closed the bad contact making the TV work intermittently. Now one or more components has opened or shorted and you must hunt it down. You are not likely to SEE the bad component. You must know which part of the circuit to test, and find and replace the defective components to make the TV work!

Reply to
Jumpster Jiver

Jumpster Jiver wrote (in news:4aa1914d$0$22507$ snipped-for-privacy@cv.net):

That?s why it?s in quotes.

Actually, I meant that reseating the cord at the plug end was more of a way of scraping of any patina that may have been on the prongs, thus impeding the flow and so making a better contact with the outlet.

Well if the flyback is the problem, then I won?t be bothering with it; I?ve got too much else to do anyway. If it?s the HOT, then I may keep it around to look at again some time in the future. If it?s something simpler like a cold joint or blown cap or resistor or invisible fuse or something, then I would like to fix it.

--
Alec S.
news/alec->synetech/cjb/net
Reply to
Alec S.

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Considering the age of the set, you'd be better off replacing it with a new one, than to invest money and time in to it. You could fix it, and then a short time later it will fail again.

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Reply to
Jerry G.

I had a TV that "blew out" on me once, and yep, it was the invisible fuse that went bad. But, I couldn't see it, so I couldn't replace it. BTW, throwing around fancy terms like "HOT" and "flyback" don't dress up your resume none around this group, so to speak, in the vernacular, like. Maybe you can fix your apostrophe key instead, so you don't have to substitute commas.

Reply to
Smitty Two

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To be fair, those are legitimate problems with TVs and I can see apostrophes rather than commas, maybe you should fix your client's encoding to display Unicode. like?

Reply to
Mike

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