Troublesome Trio of 6100's

[macman142]

I'm currently working on reviving a bunch of PM6100's (mix of 60 and 66MHz). I'm now at a point where I have three working, and three in various stages of not working-ness.

I started out by re-capping all six power supplies, which were a mix of Astec and Dyna Corp. All went well there and all six were revived with straight-forward recaps.

As usual, the logic boards have proven to be more difficult. Although none showed any visible signs of electrolyte damage (I guess more likely they dried out) I put the boards through my ultrasonic cleaner after recapping anyway. There were no mishaps during the recapping and nothing unexpected.

Three work fine. Three do not

Of the three that don't work, I have the following symptoms:

1. No chime, just a light pop. Starts up to the blinking question mark but doesn't 'see' any SCSI devices, internal or external.

2. A static-sounding chime, followed by a very loud (and clear) death chime. No video.

3. No chime, no crash, no video - nothing.

So far I have tried swapping in known-good ROM simms. None have a PRAM battery installed, so they all have always required the usual quick on/off treatment. I have double and triple checked my re-cap work (visually under magnification and also for continuity with a multimeter). I have also checked for any bent pins, solder balls or missing components. Also visually inspected all three 601 CPU's for signs of excessive heat/cracks or loose legs. All had their thermal paste renewed.

If anyone has any similar experiences, or any suggestion, please feel free to comment. I would love some clues for where to go next.

Thanks for reading!

 

[phipli]

I'm currently working on reviving a bunch of PM6100's (mix of 60 and 66MHz). I'm now at a point where I have three working, and three in various stages of not working-ness.

I started out by re-capping all six power supplies, which were a mix of Astec and Dyna Corp. All went well there and all six were revived with straight-forward recaps.

As usual, the logic boards have proven to be more difficult. Although none showed any visible signs of electrolyte damage (I guess more likely they dried out) I put the boards through my ultrasonic cleaner after recapping anyway. There were no mishaps during the recapping and nothing unexpected.

Three work fine. Three do not

Of the three that don't work, I have the following symptoms:

1. No chime, just a light pop. Starts up to the blinking question mark but doesn't 'see' any SCSI devices, internal or external.

2. A static-sounding chime, followed by a very loud (and clear) death chime. No video.

3. No chime, no crash, no video - nothing.

So far I have tried swapping in known-good ROM simms. None have a PRAM battery installed, so they all have always required the usual quick on/off treatment. I have double and triple checked my re-cap work (visually under magnification and also for continuity with a multimeter). I have also checked for any bent pins, solder balls or missing components. Also visually inspected all three 601 CPU's for signs of excessive heat/cracks or loose legs. All had their thermal paste renewed.

If anyone has any similar experiences, or any suggestion, please feel free to comment. I would love some clues for where to go next.

Thanks for reading!

Hum. I'd start by verifying voltages (under load), even with a easy recap, sometimes it results in voltage changes. Did you use low ESR caps for the output side of the PSUs to ensure stable voltages? Might be worth uploading some (high resolution, well lit) photos in case anyone happens to spot something.

Then I'd check the clocks (there are multiple). Ultrasonics sometimes kill clocks, so it might be worth checking.

The most cost effective way to check a clock (not as good as a high end oscilloscope, but we can't all afford one ) is to use one of these :

DIY Range 1Hz-50MHz Crystal Oscillator Frequency Counter Tester Digital LED PCB | eBay

Material: PCB. 1 Frequency Counter. You can select the power saving mode, if the frequency is not obvious changes within 15 seconds automatically turn off the display;. Frequency Range: 1Hz-50MHz. Crystal Test Range: about 4MHz-48MHz.

www.ebay.co.uk

That is a random listing, so find a listing that suits you best (proximity and price). Just make sure you get a red version, not a yellow one. There are assembled versions and kit versions, it isn't a difficult kit.

This frequency counters are surprisingly accurate and while they don't tell you everything about the quality of a clock signal, I use one to check if a clock signal is there at all, and the expected frequency.

The light pop means the sound system is being reset. Questions to be asking yourself are things like - does the CPU get warm after you turn it on? Does the RAM get warm?

Is any of the solder near the caps you replaced a dull grey instead of shiny?

That's a few things to be considering to start. I feel like... while we don't have the 6100 schematic that I know of, we do have the 8100, which is a fairly similar machine. It wont tell you the exact arrangement, but between that and the architecture diagram in the Developer Note, it might help understanding.

Good luck! PM 6100s are under rated machines. An 80MHz overclocked 6100 with 264MB of RAM and a 266MHz G3 is an absolute monster, and unlike many later beige Macs, you can toggle the G3 on and off by just disabling and enabling the extension.