Ms. Pac board blowing both 1A fuses?

mschwartz01

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I have a ms. pac board that was woking fine and one day just started blowing both of the 1A fuses... (F7 & F6 below) (The actually glow orange for a few seconds before frying out)

pacfuse.jpg


I originally thought it was an issue with the power supply but realized it wasn't when I put a known working ms. pac board into that machine and no fuses fried...

Any idea what can cause this? Everything was working fine and no changes were made... Thats what baffles me on this!
 
It could be a shorted cap or bad sound amp among other things. I would suspect cap C51, 330uf first since its the most common to fail. Next would be the 2200uf cap at location C29. If you have an ESR meter you can test these, if not swap them out. If your problem still exists its most likely the sound amp.
 
Check those pesky tantalum caps before you start pulling ICs
 
I have seen the tantalums short but they usually burn up when they go. In the case of a pac board your symptom usually points to those two caps or the amp. The 330uf cap is usually the first to go and the 2200 next. The LM1877 amp usually gives you signs before it up and dies but not always. Also a dead short in the amp usually results in the release of the magic smoke until it burns open.
 
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