JC8080
Well-known member
I recently picked up a Color Classic in unknown condition. The first thing I did was recap the logic board. I tried powering up (using a known-good ADB keyboard that works with soft power on my IIsi), and nothing. No beep, no fan, no hard drive spinning up. Just an extremely quiet whine that starts about a second after I turn the hard power on. Next, I recapped the analog board (all the caps with a Console 5 kit). Same result when I tried to power the machine on. I removed, cleaned, and re-installed both the CUDA and sound chip, still no change in behavior.
If I take the logic board out and turn the hard power on, the fan and hard drive spin up, and I can hear the CRT power up. No activity on the front LED light. Other posts have said you should hear a ticking noise when you start the machine without the logic board, and I do not have any ticking sound. Could that point towards something on the analog board? Or would having the hard drive connected put enough load on the PSU that the ticking would not happen?
If anyone has next-steps for troubleshooting I would be grateful for any help. A couple more points/questions below:
If I take the logic board out and turn the hard power on, the fan and hard drive spin up, and I can hear the CRT power up. No activity on the front LED light. Other posts have said you should hear a ticking noise when you start the machine without the logic board, and I do not have any ticking sound. Could that point towards something on the analog board? Or would having the hard drive connected put enough load on the PSU that the ticking would not happen?
If anyone has next-steps for troubleshooting I would be grateful for any help. A couple more points/questions below:
- Does the IIsi or LCIII have chips that would work in place of the CC CUDA or sound chip?
- The DL21 and DL22 diodes have both gotten hot in the past, the board is dark around them, which seems common. The diodes are in good physical shape. If the diodes are bad, could it cause these symptoms?
- When I beeped out the sound chip, pins 37 and 38 had continuity. I can't tell based on the Bomarc schematic if they should. I have tried with a 1/8 jack inserted, and either way I get continuity between 37 and 38. I am rather certain there is no solider bridge, unless it somehow happened way back where a dental pick slid between the pins wouldn't touch it. Schematic snip below.