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TV vertical/frame problem

I'm trying to fix this European ELBE E12D chassis tv. The inital problem was this:

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As you can see, there is a venetian blind effect, and considerable foldover. The voltages around the IC seemed normal. It looked like a pumpup cap failure, but a change of several caps didn't alter anything, so I got a new TDA 8178S frame chip. that produced only the usual horizontal line. A TDA 8170 (which was in the schematic for the set) also did the same. Re fitting the original brings back the initial fault.

Is this likely to be a case of requiring the original TDA8178 part or could there be somethign else I should pursue?

-B

Reply to
b
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IMO you have some really bad capacitors in that vertical output. An ESR meter, even a modest one like this

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er_61.html

(scroll down to IN CIRCUIT CAPACITANCE TESTER)

will give you good info but keep in mind some models have large values (1000uF) in the feedback loop. Even a very mild deterioration can cause significant linearity issues. The tester _will_ show it as not as good as a new one but still seems OK. Don't be fooled.

G=B2

Reply to
stratus46

Got the schematic. measured the voltages around IC 301 TDA 8178S, All seems Ok except pin

3, with about 12v, (1.4v on schematic) and pin 5 with about 18v. (13.8v)

Already changed c304 103k, 25v rectifier D301 1n4001. I had previously changed C308 2200UF and C310 220UF, no change.

Before I fit the new IC, I would like to rule out the possibility of something amiss on the circuit. Something does not seem right with those voltages, but I don't know if it is caused by : a) faulty TDA8178S IC (leaky) b) misprint on schematic c) the fact the ic fitted - tda8178s - differs from that specified on schematic (tda 8170) d) some problem in the vertical (frame) circuit

Any advice gratefully received. I am currently trying to upload the extract form the schematic, will post link here when I do.

Reply to
b

I am currently trying to upload the

see here

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Reply to
b

On Sun, 29 Nov 2009 09:58:52 -0800 (PST), b put finger to keyboard and composed:

Have you changed the electrolytic capacitor on the 25V rail near the FBT???

- Franc Zabkar

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Please remove one \'i\' from my address when replying by email.
Reply to
Franc Zabkar

yeah, c427 1000uF. Picture still distorted. I think I will just take a chance and change the IC again.

-B

Reply to
b

On Tue, 1 Dec 2009 06:05:54 -0800 (PST), b put finger to keyboard and composed:

Why not break out the oscilloscope and take some measurements?

I'd look at the input at R303 (not IC pin 1), and I'd compare it against the signal at the current sense resistor, R310. AFAICT, both should be sawtooths (sawteeth?).

BTW, I believe R310 should be a 1R5 resistor, not 1M5 as shown in the diagram.

- Franc Zabkar

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Please remove one \'i\' from my address when replying by email.
Reply to
Franc Zabkar

don't have a scope here (yet) so can't do much else. today I changed the IC again and was rewarded with the horizontal line. I don't understand why the original IC produces at least a distorted pic but no replacement has produced anything. In ahy case I'm losing patience with this set and have other things piling up, so I suppose it's time to dump it thanks all B

Reply to
b

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