Macintosh Classic doesn't recognize hard disks

[protek]

My Mac Classic doesn't boot from hard disk and SCSI HD tools don't recognize any drive connected to it. The drive spins and clicks once on startup but OS goes into floppy with question mark. I've tried several drives both Apple certified and others and all should be correctly jumpered and at least one is a known working drive.

This all started, when I wanted to reinstall the OS into my original drive. The installation went gaga and the original drive kicked the bucket. I got a replacement, which I managed to get jumpered correctly and it was still detected by the HD tools. The bearings of the drive were bad as it was keeping a horrible grinding noise, when spinning. The bearings must've seized or something as the whole system crashed during format. The Mac hasn't recognized any hard disks ever since.

I've changed the PRAM battery and tried to zap the PRAM to no avail. I dug the logic board out to have a closer look and wanted to get your opinion on the attached pics.

Based on the first two pics, one thing is obvious. The caps are in desperate need of a renewal. But the following picture of the SCSI chip makes me wonder. Has the seizing of the drive caused what can be seen on the picture between the two legs of the SCSI chip.

Is the board still salvageable or should I start looking for a replacement?

 

[roy_bates]

i would try to clean up all that mess and replace the capacitors,after that if it still dont work after checking for corroded traces it may be time to replace the scsi ic as well if it is dead.

 

[protek]

The board makes a perfect test subject for trying the twisty cap removal.

 

[roy_bates]

oh dear.

 

[protek]

Phew! I now know how rotten fish smells like. I removed all the SMD caps by twisting the canister. All the pads appear to be intact.

Should I try to neutralise the electrolytes and clean the board before trying to clean the pads?

How long exposure time to citric acid is enough?

 

[protek]

Threat neutralized, situation under control.

Before starting to clean the pads I decided to neutralize the electrolytes on the board. As you can see there was quite a bit of residue.

I have crystallized citric acid that I mixed with water and then poured the solution on to the board and let it be for 10 minutes.

I then rinsed the board and gave it a good scrub with IPA and toothbrush. Luckily, it wasn't as bad as I thought it might be. One copper trace is exposed but the continuities still work.

I then removed the capacitor legs and did my best to clean the pads with wick. All pads accounted for.

The next step is to solder in the new capacitors and see if that makes any difference in finding SCSI disks.

 

[protek]

Well, new caps are in place. Or at least I hope they're in place. Well, still no hard disk recognition but I can now hear the chime in boot. On the other hand it no longer boots from ROM. I do hear the hard drive clicking and spinning.

Don't really know what else to try other than trying to change the SCSI chip, or the whole logic board.

 

[jcarvalho]

Replace 3 caps on SCSI HD board, worked for me like a charm!!!! SCSI fully working now

You can also try the finger trick. for that you need to open the hard drive cover, exposing the plates and the reading head and when the drive starts to spin, give a touch in the head to unpark it, then close the cover to avoid dust... When you turn off the disk you need to repeat the trick...
Regard,
Jorge

 

[protek]

I suppose I have to reflow the new caps again.

 

[protek]

Yay, it's working again! New caps and a jump wire did the thing. Had to ask a friend to redo the SMD caps as I'm still not confident enough to do it myself.

Funny thing is that it's actually working with the original hard drive, which I thought to have gone bad, when it was in fact the caps that caved in. Nice to have my Mac up and running again.

 

[protek]

I was finally able to finish what I started probably over a year ago, to make a clean OS install on my Mac. My first attempt went south, when the hard drive failed, when trying to initialize it. I falsely assumed that the hard drive was at fault, when it was the leaking caps that caused the problem. I spent the whole year looking for a replacement. In the end, I'm using the original drive to run my OS.