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Wpc sound brd fuses blowing

Mooseman

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Feb 10, 2012
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Runcorn
A friends dr who Pinball wpc sound board is blowing both 3a fuses on power up.
C26 cap had blown apart and a trace on the back had destroyed itself. Re newed the 1uf tant cap and the trace. Also volt reg u3 and u4 replaced because I had some. The big 4700uf caps don’t look domed but I’ve ordered some.
Any sound board experts that could point me to the real culprit?
Many thanks
 
So got the 47000 caps. Having desoldered the old ones I tested them on my fancy Chinese tester and they were actually still good. They will be changed for fresher and newer though. Once these big caps were out of the way another tant cap was found blown to bits at c46 and then if you look real closely u1 has a crack in it the lm1875 audio amp. Think we’re getting somewhere. Now need to find that component.
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Changed the amp chip the other blown tant cap the 2 big caps and hey presto


Still blows both fuses ?

Bollockyboo
 
Moose,

AIR the audio pcb develops its own 12v power using those large MR501 diodes, D1 thru 4, as a bridge rectifier. One or more of them may well have short-circuited, becoming simply wire conductors
 
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Will get my meter on them thanks. I was concentrating on all the visibly broken stuff and thought yay cracked this.
Was well deflated when it still went bang.
Think Jim needs to design a wpc audio board replacement as reading up they seem like hens teeth getting replacements
 
Ok so the board is now fixed thanks to my good Dr @DrPinball
It seems that even when you fit new components like voltage regulators they can also be broke from new.
There is deffo a market out there for a wpc soundboard replacement if you can get around this unobtanium chip thats on there.
@myPinballs
 
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When fitted in the Dr Who the amp chip blew again. It turned out the mid sized tweeter on the left was at virtually 0 ohms or as near damm it thus causing the board to work to hard and blow up. New speakers ordered and hopefully a successful mission. Big thanks to Dr pin for his help and tec knowledge.
 
You'd think there would be some kind of failsafe for faulty speakers, wouldn't you? Blowing a chip apart seems like an extreme failure condition...
 
Had all sorts of issues with this board. The tantilum capacitors go with a bang and usually flames ?
Nasty little buggers
 
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