I own volcano and changed the caps in the base cab first.
Later i had the sound just disappear at random. Had to change the dips.
You just never know on the old gottliebs.

My game is in maine and i am in massachusetts.
I looked thru all my pics but i cannot idenify which sound board i have.
I may be up there next week.

FWIW i believe my game has the board that matches the schematic in the volcano manual. When i had to work on it, the board components matched up with the schematic.

Drawing is posted in your other thread

Waiting....
If that doesnt work are you going to change the resistor rp1 rp2?

Have you tried contacting Ed at GPE and asking him if he has any ideas?
He has helped me out in the past and he has knowlegde of the comoonents on that board as well as early SS Gottliebs.
He is on this forum or you could email him at Great Plains Electronics.

Are the pots original?

The 7407 may have been changed as you say but it is dated 1980 which would make the swap very early in its life.

I admire your tenacity.
By now i would have shot gunned this board with every part i could find.
I once replaced every component on a stern sb-100 to make it work correctly.

Just curious if there is a date code on your sc01A?

My game does groan when shut down. Never paid much attention to it.
I do not have any unusual sounds at start up though.

Yeah, power down with sound on. Not always the same but there most if not all the time.

Maybe you should look at this in reverse. It makes the noise at power down. What is happening then.

Hoping it is finally solved.
Great job. As i said previously, i admire your tenacity.
Gives me hope i can solve the problem i have with my TZ.

I had it 10 seconds. It stayed that way because I did not want to move the game out to get into the head.
The other day the 5101 puked.
I was in there and changed it to 4 minutes. Tested it before removing the MPU.
It was driving me crazy at 10 seconds.

There is voodoo in that SC-01 !!