This is a continuation of this old thread that described the following boot issue on my 1981 Gottlieb Volcano (System B, Gen 2). I erroneously thought I had found and solved the issue 8 years ago. Then I left the game sit and only recently got back into it.

Randomly...

1. Turn on switch.
2. Clunk... ball release and ball kicker solenoids engage and stay engaged. Both on same fused circuit. Both also have the under playfield transistors that are triggered by lamp drivers. (I've since added the recommended pull-up resistor to these). The red "extra ball" lamp near the drain lights up.
3. Simultaneous to #2 above, credit display brightly shows "0" and score displays remain blank.
4. Wait a couple seconds, nothing changes; and it would stay like this until fuse blows or solenoids smoke.
5. Turn off switch as quickly as possible.
6. Go back to step 1.

It's getting worse. Some days I never see this happen and other days I have to repeatedly turn the game off/on before I get a normal boot up and can play. During play, it's perfectly fine however. It's only an issue when first turning on the machine.

Today, I dug into the MPU again and although it had some minor battery damage more than 10 years ago that a previous owner fixed. I found and cleaned off more corrosion which led to the following repairs...

1. Replaced the standard socket for Z2 with a strip socket and verified good solder connection on top and bottom side of board. The old chip socket was full of green corrosion.
2. Removed original Z3 and added a strip socket and new 7404 chip.
3. The legs of Q4 were almost corroded completely through and cracked off when cleaning. Replaced with a new 2N3906.
4. Resistor R6 cracked off where the lead connects to resistor body. Replaced.
5. Removed, cleaned, and re-soldered the clock crystal and resistors R3, R4, and R5. Physically, the crystal looked fine with only minor corrosion on the bottom ends of the legs where they were soldered.
6. I carefully checked and cleaned off any corrosion, and found no more broken leads or traces.

The booting problem persists... again, if I toggle it off/on several times, I can get a good boot and play normally.

I went through Clay's guide for checking a MPU with a logic probe and discovered that the crystal only shows a clock signal on the bottom leg. The top leg is showing a steady low. For some reason I'm having trouble with the grammar or wording of the guide and just not 100% sure if I'm supposed to see a clock pulse on both legs of the crystal? Resistors R3, R4, and R5 tested good when I had them off the board. I did not replace because I did not have those exact values on hand.

Following more tests in Clay's guide, I am seeing a clock pulse at the other pins as indicated... U4, U5, U6, etc.

Is the crystal supposed to show a clock pulse on both legs? Could something like a half-dead crystal explain why it boots sometimes and not others? Timing issues on the power-up sequence? Looking at the schematic, I imagine that half the clock's square wave might be missing. I just don't understand how it still plays normally if that's the case. Does this make any sense and can anyone shed any more light on this? Thanks.