Hi everyone!
I recently purchased a few original Macintosh II systems (all with rev. B motherboards) and am working on getting them going again. after a good amount of work (recapping, washing board, cleaning RAM and patching traces) I've brought one machine back to life. There were a few bad traces I had to patch to allow the power button to turn the unit on and off again, as the soft power circuit wasn't working. I installed system 7.5 on the original Quantum HD and everything is working well (mostly).
Now that the soft power circuit is up and running again I noticed the computer will drain one of the batteries overnight if it's left off. If the machine is on, there's no battery drain. I checked resistance between the battery terminals on each holder and it's in the megohms. What else is odd, is whatever kind of short or partial short is happening to drain the battery, it's very intermittent. I had the machine sitting on the bench last night, powered off, and the batteries held stable voltage until about 2.5 hours in when they started draining. If the batteries are both good, the soft power circuit works perfectly, and even jump starting the power supply works fine. I also noticed that sometimes if you unplug the power cable from the power supply to turn it off, the relay inside will make a rapid clicking sound as the internal caps are discharging, almost like the system is constantly telling it to power up.
I'm wondering if it's possible that Q3 is turning itself on and off somehow (almost like an intermittent short) as I do know this is one of the only parts that will consume power. I have checked all of the diodes in the power circuit and none are shorted. I did remove Q3 and it seems to test okay, and I also cleaned the pads underneath it to make sure there wasn't any junk under there. I will be ordering Q2 and Q3 as well as UB1 and UB2 and replacing them all just for good measure.
I have not recapped the power supply yet, but I tried 3 different supplies and the same thing happens with all of them, so I'm leaning towards a logic board issue.
If anyone has any ideas, that would be appreciated!
I recently purchased a few original Macintosh II systems (all with rev. B motherboards) and am working on getting them going again. after a good amount of work (recapping, washing board, cleaning RAM and patching traces) I've brought one machine back to life. There were a few bad traces I had to patch to allow the power button to turn the unit on and off again, as the soft power circuit wasn't working. I installed system 7.5 on the original Quantum HD and everything is working well (mostly).
Now that the soft power circuit is up and running again I noticed the computer will drain one of the batteries overnight if it's left off. If the machine is on, there's no battery drain. I checked resistance between the battery terminals on each holder and it's in the megohms. What else is odd, is whatever kind of short or partial short is happening to drain the battery, it's very intermittent. I had the machine sitting on the bench last night, powered off, and the batteries held stable voltage until about 2.5 hours in when they started draining. If the batteries are both good, the soft power circuit works perfectly, and even jump starting the power supply works fine. I also noticed that sometimes if you unplug the power cable from the power supply to turn it off, the relay inside will make a rapid clicking sound as the internal caps are discharging, almost like the system is constantly telling it to power up.
I'm wondering if it's possible that Q3 is turning itself on and off somehow (almost like an intermittent short) as I do know this is one of the only parts that will consume power. I have checked all of the diodes in the power circuit and none are shorted. I did remove Q3 and it seems to test okay, and I also cleaned the pads underneath it to make sure there wasn't any junk under there. I will be ordering Q2 and Q3 as well as UB1 and UB2 and replacing them all just for good measure.
I have not recapped the power supply yet, but I tried 3 different supplies and the same thing happens with all of them, so I'm leaning towards a logic board issue.
If anyone has any ideas, that would be appreciated!
