MK2 Sound Board Repair

zenomorp

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Posting this in the hopes that it might help someone down the road. I acquired this board in a semi-working state. When I first turned it on, there was no test tone, but the LED would come on. After about 10 seconds, there was a pop...then the sound would work, but it was a bit static-y. Then, after about a minute, the sound would cut in and out completely and then fade away all together. The amp and heat sink were scorching hot!

So I knew the amp was working, but it was cutting out due to heat. I re-flowed it for good measure. The next step was to determine why it was overheating. The board looked ok physically, so I start looking at the socketed chips. I noticed on the U17 GAL that one of the legs was bent under the chip. I straightened it and reinstalled the chip. Success! I got the test tone at start up, no more scorching amp (although it could use some more thermal paste to help because it's still a bit warm)...but I still had the static.

I decided to replace ALL the caps near and around the amp. Fortunately, I had a spare parts board to get them from that most definitely had other issues, trust me. I was confident the replacement parts were good, and they were! After changing all the caps, I fired up the sound board and it's now working flawlessly. Been running for over and hour with no issues. Just wanted to share. FIGHT!















 
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I love fixes like this.

Good work xeno.. it still blows my mind the number of axial caps on these things.. these... midway sound boards...
 
I love fixes like this.

Good work xeno.. it still blows my mind the number of axial caps on these things.. these... midway sound boards...

same amount as the previous model I think.

Williams certainly dropped the ball on where they placed them on this board though. lol
 
Now looking at it, you are totally right, it would have made more sense to put the axial caps on the back side of the pcb, so its not sitting right under the passive heat sink... or raise the heat sink further from the pcb.. but prob beat bet is to rig a 12v computer fan blowing at the board on. 90degree angle to how the pcb will be mounted..

Heat and old caps left on for hours at a time, yep you nailed it!!
 
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