Mac Classic - will it ever run again!!
Posted: Sat Aug 01, 2020 2:33 pm
I've been the owner of several Macs over the years. A couple of Macbooks (G3 & G4), a couple of Performas (I still have one and it runs just fine) and a 17" Powerbook G4, which I bought for £40 as spares or repairs, and had it fixed and running OSX within a day of it arriving.
The other machine I've owned for quite a while is a Mac Classic. Up until around 6 months ago, it was running ok, but I recently powered on and it's not so well any more. Since its a retro machine and 68K based, I thought that I would pull it out of my more general blog and into one all of it's own, for hopefully better coverage and assistance.
The symptom is that when the machine is powered on, I get a checkerboard pattern on screen. It also has a wobble/ripple to it, but that does seem to stabilise after warming up a bit. Removing the RAM daughterboard gives a different pattern on screen of close horizontal bars.
Aside from joining 68kmla and watching the entire Mac Repair-a-thon series on Adrians Digital Basement, here's what I have done up to now:
1. Removed the 7 capacitors that are known to leak on the logic board, and replaced with tantalum equivalents. (Note the picture of the mobo shows C5 and C9 missing, these were taken out to troubleshoot a non-existent short.
2. Cleaned the area around the caps with IPA and thoroughly washed the mainboard in soapy water and dried for 48 Hours.
3. Replaced the leaking PSU capacitors on the analog board.
4. Possibly killed the ROM. It has a 42 pin socket, and for 40 pin ROMs should be plugged in starting at pin 2. I mistakenly plugged into pin 1 and it got rather warm.
Here is the logic board:
And you can see that there appears to be no corrosion visible around any of the chips. I have checked very close up with a microscope. Luckily the battery didn't leak, and if the logic board caps did leak it wasn't much at all. Although the analog board caps did leak, it wasn't much and was restricted to around the capacitor bases.
The current situation is that I am working to replace the ROM (Possibly with one of @cmorley's ROM emulators. That's a task for this weekend.
I still get the checkerboard display, and with the logic board connected, the voltage is dropping from 5v to 4.7v, which is below the threshold for the machine to run from what I've been told. I can adjust this, so will do so under load to see if it makes a difference, but I am also going to replace the PSU optocoupler as a thread on 68kmla suggested it's common for them to fail.
I'm grateful so far for everybodys suggestions over on my Stuff and Things thread, but I thought it time it had a thread of it's own.
Any help and suggestions gratefully received as these things are new to me.
The other machine I've owned for quite a while is a Mac Classic. Up until around 6 months ago, it was running ok, but I recently powered on and it's not so well any more. Since its a retro machine and 68K based, I thought that I would pull it out of my more general blog and into one all of it's own, for hopefully better coverage and assistance.
The symptom is that when the machine is powered on, I get a checkerboard pattern on screen. It also has a wobble/ripple to it, but that does seem to stabilise after warming up a bit. Removing the RAM daughterboard gives a different pattern on screen of close horizontal bars.
Aside from joining 68kmla and watching the entire Mac Repair-a-thon series on Adrians Digital Basement, here's what I have done up to now:
1. Removed the 7 capacitors that are known to leak on the logic board, and replaced with tantalum equivalents. (Note the picture of the mobo shows C5 and C9 missing, these were taken out to troubleshoot a non-existent short.
2. Cleaned the area around the caps with IPA and thoroughly washed the mainboard in soapy water and dried for 48 Hours.
3. Replaced the leaking PSU capacitors on the analog board.
4. Possibly killed the ROM. It has a 42 pin socket, and for 40 pin ROMs should be plugged in starting at pin 2. I mistakenly plugged into pin 1 and it got rather warm.

Here is the logic board:
And you can see that there appears to be no corrosion visible around any of the chips. I have checked very close up with a microscope. Luckily the battery didn't leak, and if the logic board caps did leak it wasn't much at all. Although the analog board caps did leak, it wasn't much and was restricted to around the capacitor bases.
The current situation is that I am working to replace the ROM (Possibly with one of @cmorley's ROM emulators. That's a task for this weekend.
I still get the checkerboard display, and with the logic board connected, the voltage is dropping from 5v to 4.7v, which is below the threshold for the machine to run from what I've been told. I can adjust this, so will do so under load to see if it makes a difference, but I am also going to replace the PSU optocoupler as a thread on 68kmla suggested it's common for them to fail.
I'm grateful so far for everybodys suggestions over on my Stuff and Things thread, but I thought it time it had a thread of it's own.
Any help and suggestions gratefully received as these things are new to me.