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Old 7th November 2012, 03:26 PM   #11
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Thanks Mooly!
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Old 7th November 2012, 04:52 PM   #12
Mooly is offline Mooly  United Kingdom
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That doesn't look to scary

Its always nice to fault find properly by measurement but just looking at the PCB the stand out and perhaps more obscure failure items would be the two tantalum capacitors and the ceramic caps. Other things to check first though.

The two blue electroylitic caps look as though they could be rail decoupling. Try and confirm if they go to the power pins of the IC's. There are two ? diodes at the right hand side next to one of these caps. Always worth a check as they are a typical failure item. There are a handful of small signal diodes scattered around. Again always worth a check for leakage. Without a circuit I wouldn't like to say what these do. They could be related to the PSU or some on/off thump suppression. You would have to check them out of circuit (just lift one end) for leakage.

The resistors and the poly caps almost certainly OK. That just leaves physical damage such as a broken track.

If you can determine the PSU connections then powering this up with two 9 volt batteries is a real possibility and would allow you to compare the good and bad PCB's.

I'm assuming it does run on dual (split) supplies going of the two blue electros but you need to be sure. See where the IC power pins go.
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Old 7th November 2012, 05:20 PM   #13
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R1 looks a bit discolored.
Also, I don't think I ever run across caps that look like those, eg C17, C7, C14. They look like SMT with radial leads added on.
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Old 7th November 2012, 05:37 PM   #14
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by sofaspud View Post
R1 looks a bit discolored.
Also, I don't think I ever run across caps that look like those, eg C17, C7, C14. They look like SMT with radial leads added on.
They are polyester film box capacitors
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Old 12th November 2012, 03:13 PM   #15
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Hey guys.
I fixed the problem, it was one of the polyester capacitors "C17, C7, C14..."
Cheers for the help.

Just one quick question, when you guys need to check a cap, do you cut one of the legs from the board or do you unsolder them?
I measure them with a analog multimeter, is it a full proof test?
thanks!
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Old 12th November 2012, 04:03 PM   #16
Mooly is offline Mooly  United Kingdom
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That's great you have fixed it. Well done

I'm really surprised it was a polycap that was duff but yes, testing on an analogue meter on a high ohms range usually shows leakage particularly if its like an old AVO that uses a 15 volt battery. I would always just try and desolder one end with braid providing that's possible... single sided PCB, component legs not twisted and embeded in the PCB etc. No test with any meter can determine fully if the cap is good though, although most cap problems on non electros are leakage related.
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