Quoted from thedefog:

I've run into issues with CMOS 555 timers not working where non-CMOS ones do. If you have a Radioshack nearby, they probably sell both standard and CMOS 555 timers. I know mine does at least. I've not run into this with a pinball board, but on an 80's era piece of computer hardware. I honestly can't even remember what it was, but I discovered it by accident, then confirmed it by reading about the differences between them.

Quoted from vid1900:

Yep, but you need a SHARP pair of micro diags.
Look for a good brand like Xcelite.

Quoted from thedefog:

I've run into issues with CMOS 555 timers not working where non-CMOS ones do. If you have a Radioshack nearby, they probably sell both standard and CMOS 555 timers. I know mine does at least. I've not run into this with a pinball board, but on an 80's era piece of computer hardware. I honestly can't even remember what it was, but I discovered it by accident, then confirmed it by reading about the differences between them.