Popping noise and foul smell?

[mark1120]

I recently took all my 3902 boards over to Interstate Battery to have them solder on some battery cell holders.  Yesterday, I started testing the boards to make sure the soldering was a success.  I used two machine cabinets and the same 22 chip to test about 30 boards.  My last 2 tests have not gone well.  When I inserted a board in machine "A", I heard a popping noise and experienced a foul smell.  I then tried a new board in machine "B" and experienced the same popping noise and foul smell.  I now see black marks in the same area underneath the multimedia lite boards.  Do you think it’s a coincidence that these failures happened consecutively (different boards in different machines) or could something have happened to my 22 chip that will also cause a similar failure on my next test?  Am I somehow overworking the chip or the machine cabinets with all these tests?  If I just replace the multimedia boards, do you think the main board, software, machine cabinets, etc. will be ok?  The last thing I want to do is damage the machines.  Thanks for the insights!

[Tilt]

Seems unlikely, but I think it was just coincidental.  C59 is a filter capacitor that filters the +13VDC power going into a +5VDC regulator used for the audio.  If nothing else is wrong with the MPU board it will work without it.  Audio may have a bit more hiss and humming in it though.

I've had a couple of C59s go up in smoke too.  It's rated at 16V, with 13V being applied to it continuously and over time fails.  A 25V rated cap would have been a better choice.

Your keychip definitely didn't cause them to smoke.

The MPU board on the left side of your photo has other issues too.  It's missing U74 for sure and I can't really determine from the photo, but looks like it may be missing a couple of resistor packs (RP16/17) right below U74 as well. 

C69 is the same as C59.  You could take C69 off of the MPU missing other components to replace C59 on the other MPU board if you wanted to.