I'm trying to repair this vintage programmable analog drum machine on my bench. It was water damaged, and it looks like it's been sitting in a basement and hasn't worked in a very long time. I've cleaned up the PCB and underneath the rust residue it looks OK, and I've replaced all the electrolytic capacitors and removed any signs of corrosion. It's showing signs of life now, and occasionally produces sounds that seem vaguely correct, but still isn't working properly.
Here's the schematic:
It's a pretty crude machine by today's standards - there's no microprocessor. Just what seems to be a CMOS static RAM chip that the patterns are manually bitbanged into by the user in "write" mode, and then clocked out of in "play" mode. The logic outputs of the RAM IC then trigger four different analog sound generation circuits on the right...for example the bass drum seems to be based on a transistor phase-shift oscillator, etc.
The first big problem I see with my scope is that the there's no clock coming out of the clock generator when I try to set the machine to "play" - tracing backwards it looks like the output at pin 3 of the flip flop made up of two sections of a 4011 (what's the deal with those symbols?) is oscillating at about 4 Hz, and the nominally active-low inputs of the flip flop are totally unresponsive to button presses or manually pulling them low with a jumper.
On the scope the oscillation looks like a slow "inverse" exponential decay from high to low, followed by the output of the flip flop slamming low for a little bit and then rapidly coming back up and repeating. It looks like the on-off duty cycle is about 90%.
Any idea what could be going on here?