I had a working CPU for a Gottlieb Volcano (system 80, 2nd gen) that only needed a little more cleanup... it booted 95% of the time and needed a new reset circuit. While waiting on my reset circuit chip, I worked on the playfield.
Then after changing some capacitors on the sound board and doing some playfield work, like adding the capacitors to the slingshot solenoids, I booted up successfully a few times and then bam... nothing. Going back and reviewing everything that I had done, it turns out that when I took off the spinner assembly I moved it over to where it was touching one of the leaf switches for a slingshot kicker. So when I turned it on, I sent 38 volts to pin 14 on A1J6... I can even see the mark on the side of the kicker switch.
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It comes up to all zeros as if the tilt switch was held closed. All three tilt switches are verified open.
After a bit of troubleshooting...
1. Still have a clock.
2. I have the Reset signal. U1 pin 40 goes high within ½ second. Touching pin 40 to ground does not force game to boot.
3. I have the RDY signal. U1 pin 2 goes to 5 volts.
4. IRQ never goes to pulse. U1 pin 4 stays at 5 volts.
When I realized that the spinner circuit was crossed with 38 volts, I started testing the switch matrix chips.
I tested Z15 with a logic probe and a DMM in diode mode. Output pin 11 is dead.
Afraid to power it up, I just used diode mode of the DMM to test Z11, Z12, Z13, and Z14.
The gate on Z14 that is directly connected to pin 14 on A1J6 is blown too. The only DIP turned on in that row was 28, which explains pin 11 on Z15.
I have some new 74x chips coming today, but I'm wondering if I could have damaged the U4 Riot chip as well? The fact that it's coming up as if a tilt switch is closed is an encouraging sign, I'm hoping. Fingers crossed that when the 38 volts blew through those chips, it went out the ground pin and nowhere else.
Aside from the obvious, my stupidity, any thoughts?