cj_reha
Member
Hi all,
I have a Macintosh Classic here I have been working on for a friend during the past few weeks, and at every step of the process it has fought tooth and nail to stay dead! I am at a point now where it has an issue I've never seen before and am not sure how to go about fixing, or even where to go to start diagnosing the problem. This machine in particular has been pretty severely damaged by capacitor corrosion - there was a considerable amount of damage in the output stage of the power supply, and I ended up having to desolder almost 3/4ths of the ICs on the logic board so I could reflow all of the corroded vias and verify there weren't any broken traces.
After about a week's worth of corrosion cleanup, it seemed to be working well and everything functioned as it should. I tore the machine down completely to do some finishing touches and to clean/relube the floppy drive, but when I put it back together, the machine no longer read disks from the internal floppy drive. I thought perhaps I had made a mistake when cleaning the drive itself, so I swapped in a known-working logic board from my personal Classic, but the drive works with that board without problem. To clarify, the system boots fine off the internal hard drive and everything else (i.e. audio, keyboard/mouse, etc) functions as it should, the machine just does not make any attempt to read floppies. When a disk is inserted, the drive will spin up and the head positions itself, but it makes no attempt to seek and the disk stops spinning after a few seconds. If I brute force eject the drive and reinsert the disk, the head no longer moves at all and the drive just spins/stops.
The only causes I can logically think of are that perhaps the SWIM chip somehow got killed by ESD, or somehow from me discharging the CRT? I made sure to be gentle with the board and not rub it against anything, since there are a few patches for missing pads/broken traces I made that are somewhat precarious and fragile. The SWIM was hit pretty hard by the cap damage and there was a fair amount of blue corrosion on the pins, so perhaps some internal connection was damaged enough to fail after power was applied for some time? They seem to be a pretty far-fetched theories, but I legitimately have no idea as to how it could have just spontaneously died like this.
I'm at my wit's end with this computer and I just want to see it work reliably so I can get it back to its owner. I'm going to try to swap in the good SWIM off my personal machine's logic board to see if the "dead SWIM" theory is right, but beyond that and manually tracing out the pads to make sure a via didn't open up or something, I have no idea what to check. Any input is thoroughly appreciated and I thank you all for reading this, I hope this story has a happy ending! :huh:
P.S. the attached photo shows the computer with a System 6.0.8 disk inserted in the drive which is tested good in another machine; the system acts as if nothing is in the drive.
I have a Macintosh Classic here I have been working on for a friend during the past few weeks, and at every step of the process it has fought tooth and nail to stay dead! I am at a point now where it has an issue I've never seen before and am not sure how to go about fixing, or even where to go to start diagnosing the problem. This machine in particular has been pretty severely damaged by capacitor corrosion - there was a considerable amount of damage in the output stage of the power supply, and I ended up having to desolder almost 3/4ths of the ICs on the logic board so I could reflow all of the corroded vias and verify there weren't any broken traces.
After about a week's worth of corrosion cleanup, it seemed to be working well and everything functioned as it should. I tore the machine down completely to do some finishing touches and to clean/relube the floppy drive, but when I put it back together, the machine no longer read disks from the internal floppy drive. I thought perhaps I had made a mistake when cleaning the drive itself, so I swapped in a known-working logic board from my personal Classic, but the drive works with that board without problem. To clarify, the system boots fine off the internal hard drive and everything else (i.e. audio, keyboard/mouse, etc) functions as it should, the machine just does not make any attempt to read floppies. When a disk is inserted, the drive will spin up and the head positions itself, but it makes no attempt to seek and the disk stops spinning after a few seconds. If I brute force eject the drive and reinsert the disk, the head no longer moves at all and the drive just spins/stops.
The only causes I can logically think of are that perhaps the SWIM chip somehow got killed by ESD, or somehow from me discharging the CRT? I made sure to be gentle with the board and not rub it against anything, since there are a few patches for missing pads/broken traces I made that are somewhat precarious and fragile. The SWIM was hit pretty hard by the cap damage and there was a fair amount of blue corrosion on the pins, so perhaps some internal connection was damaged enough to fail after power was applied for some time? They seem to be a pretty far-fetched theories, but I legitimately have no idea as to how it could have just spontaneously died like this.
I'm at my wit's end with this computer and I just want to see it work reliably so I can get it back to its owner. I'm going to try to swap in the good SWIM off my personal machine's logic board to see if the "dead SWIM" theory is right, but beyond that and manually tracing out the pads to make sure a via didn't open up or something, I have no idea what to check. Any input is thoroughly appreciated and I thank you all for reading this, I hope this story has a happy ending! :huh:
P.S. the attached photo shows the computer with a System 6.0.8 disk inserted in the drive which is tested good in another machine; the system acts as if nothing is in the drive.
