I have been working on bringing an old Macintosh II back to life. I'm not new to the process, but this one is stumping me.
- replaced both batteries
- replaced all the 47uF SMT caps
- replaced all the radial electrolytics for good measure
- repaired a failed trace in the power circuit (somehow I've had more than a few IIs and IIxes with this fault)
- cleaned the board with flux cleaner, then again with 99% isopropyl
- tested the assorted PSU rails
Symptoms are, power switch works to turn the machine on and off, ADB works to turn the machine on. No bong, no crash sound. Even if I remove the memory, I don't get a crash bong. RESET seems to be held low, so the CPU never comes out of reset.
I'm not sure if this is meaningful, but watching the RESET line relative to logic ground, I see 0V at power off, then it slowly climbs to 0.175V when the machine is switched on.
Clues, other tests to run? Thanks!