Troubleshooting Sound - Space Invaders Pin

[Toadie]

Ok so I've pretty much accepted the fact that I'm knocking out problems one by one and realizing that more appear as I correct older ones.  In an odd way it's cool, but its getting tiresome.  Unfortunately I need to provide you with the history as I think it's relevant...

Step 1 - Got the machine home, most lights worked, sound worked, no solenoids fired
Step 2 - Replaced Solenoid Driver Board and MPU due to corrosion - Installed, burned up outhole kicker coil which shouldn't have happened with the new SDB.
Step 3 - Disconnected burned coil, played game  - Everything worked... for one night.  Next day, noticed the F5 fuse was blown, game worked, but no sound
Step 4 - Shipped SDB back and while waiting got new coils, and began troubleshooting oddly burned out lights.
Step 5 - Got new rectifier board, new SDB arrived, installed everything, everything works.... no sound 

Here's what I know....

Voltages across the rectifier board and SDB measure our correct with the regular plus or minuses
Voltages on the sound board (AS-2518-51) measure as follows : TP3 is ground. TP2 and TP1 measure 5VDC and 15VDC respectively.  Note that TP1 should technically read 12VDC but I believe that gets regulated.  Am I wrong?
MPU LED blinks 6 times and goes dim green which according to the manual indicates a problem with the sound board
Speaker, pot, and amp work as the noise level changes when I play with the volume

There is a reset button and I've tried pressing it but I don't know if there's a procedure for it like press release or press hold etc.

Inital thoughts?  I'm still going through my trouble shooting.

[Toadie]

Well I got it but I don't understand why...

Swap the 6821 PIA at U2 on the sound board with either U10 or U11 on the MPU, and retest.

Did this with the U10 from both of my MPU's, and nothing happened.  In fact the system wouldn't even boot up so to speak.  Solid LED on the MPU, no pre on tests, system would just hang.  What's the connection between the U2 on the sound board and the U10 or U11 on the MPU?

Moved on to the next test swap the 6810 RAM at U10 on the sound board with the 6810 at U7 on the MPU and retest.

Did this... and it worked?  What's the connection between the U10 and the U7?  It's just ram isn't it?

[TopJimmyCooks]

May have had two good 6180's but bad contact on a chip leg to trace, and swapping them fixed it.

[ChadTower]

I think Jimmy is on to something.  If you have the skill you need to swap out those sockets.  This is only a temporary fix and it will be a problem again as soon as that socket is jostled.