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8100/80AV Unstable

Qrani

Active member
I (somewhat) recently got a Power Macintosh 8100/80AV. When I first got it, I could never get it to start up... But just through reseating RAM, L2 Cache & ROM cards, and the video card, as well as cleaning off the motherboard, I've gotten it to start up most of the time. However, it's pretty unstable. A lot of times when trying to run a program it will crash, sometimes even just out of no where. One time I started it up and all of a sudden the sound was working. Then after a few restarts, it stopped. One of the common errors it gives is that there's "no FPU installed" or something along those lines, which would be odd, given that the CPU has an FPU built in. This leads me to believe that there's an issue with the CPU. There is some corrosion on some of the CPU's pins, I suspect from the poorly placed capacitors right next to it. But I've cleaned them off multiple times and they don't seem to be touching at all. I'm currently waiting on caps to arrive, which will hopefully fix any issues, but I'm afraid that it won't.
 

3lectr1cPPC

Well-known member
Let us know how it goes - could be PSU as well? Maybe?
I've heard many stories about unreliable 8100s, they seem to have some problems.
 

Qrani

Active member
I'm 99% confident it's not the PSU. I've tested it with a multimeter, showing all the correct voltages. I've also tested it with the PSU from my Power Macintosh 7500, which also shows correct voltages, and it still has the same issues.
 

Nixontheknight

Well-known member
I'm 99% confident it's not the PSU. I've tested it with a multimeter, showing all the correct voltages. I've also tested it with the PSU from my Power Macintosh 7500, which also shows correct voltages, and it still has the same issues.
Macs around this era were part of the capacitor plague, so you should try looking at the capacitors in the PSU and on the logic board with an ESR meter
 

joshc

Well-known member
These need recapping by this point, at the logicboard level. The PSUs can be weak too. But the 8100 is a very finnicky machine - can also depend on what OS version you are using, it could be partly a software issue as well.
 

Qrani

Active member
Did you apply new thermal grease to the CPU?
Yes, I applied new thermal paste to the CPU, since it's not the 100MHz or 110MHz model with the thermoelectric cooling device.

These need recapping by this point, at the logicboard level. The PSUs can be weak too. But the 8100 is a very finnicky machine - can also depend on what OS version you are using, it could be partly a software issue as well.
Yes, I'm going to recap the machine (which you would have known if you had read the post fully). As for software I've tried two different versions of System 7.1.2 I've found online. I assume it'd would work with the software specifically designed for it, but I could try something like 8.6 or 9.1, just to see if it works, though that wouldn't be what I'd want to run.
 

Phipli

Well-known member
As for software I've tried two different versions of System 7.1.2 I've found online. I assume it'd would work with the software specifically designed for it, but I could try something like 8.6 or 9.1, just to see if it works, though that wouldn't be what I'd want to run.
Grab a copy of 7.6.1, its a good middle ground for the 8100.

which you would have known if you had read the post fully
Ah come on now, they're only trying to help. We all skim read things sometimes. I haven't even read your original post. :)
 

Qrani

Active member
Grab a copy of 7.6.1, its a good middle ground for the 8100.


Ah come on now, they're only trying to help. We all skim read things sometimes. I haven't even read your original post. :)
I know, but still. I also don't really like System 7.5 or Mac OS 7.6. Mostly because of the look of it, something's just off. Mostly I don't like the help icon on the menu bar in the top right. It looks a lot better to me in System 7.0 and System 7.1. When I get the thing fully working I plan to dual boot System 7.1.2 and probably a later OS, like maybe 8.0 or 8.1. But not Mac OS 7.6.
 

Qrani

Active member
Of course, I could use ResEdit to make it look better, but I just want to use the original OS anyway
 

joshc

Well-known member
which you would have known if you had read the post fully
I did read your original post fully. I mentioned it again as confirmation and reaffirmation that I agreed it being worthwhile doing that.

7.1.2 is known for being unstable/buggy on these machines and wasn’t shipped with them for long.
 

3lectr1cPPC

Well-known member
If you don’t mind - I could use a photo of the 8100 logic board for the cap reference section on my website. If you have a chance, I’d really appreciate it.
 

Qrani

Active member
If you don’t mind - I could use a photo of the 8100 logic board for the cap reference section on my website. If you have a chance, I’d really appreciate it
8100_80_MB.png
There you go. Not the best photo ever, but it works. All the same values, 47uf 16v, and 13 total.
 

Qrani

Active member
Anyways, it now appears that it won't boot System 7.5.3, Mac OS 8.0, Mac OS 8.1, or Mac OS 9.0.4. Even with System 7.1.2 it's reluctant to boot from CD. So I tried a different CD-ROM drive from my PowerMac 7500, still doesn't work. I've gotten it to boot 7.5 from floppy before (using a different floppy drive, as the one in it doesn't work at the moment - I haven't gotten around to cleaning it), so I'll try that again next.
 

Phipli

Well-known member
Anyways, it now appears that it won't boot System 7.5.3, Mac OS 8.0, Mac OS 8.1, or Mac OS 9.0.4. Even with System 7.1.2 it's reluctant to boot from CD. So I tried a different CD-ROM drive from my PowerMac 7500, still doesn't work. I've gotten it to boot 7.5 from floppy before (using a different floppy drive, as the one in it doesn't work at the moment - I haven't gotten around to cleaning it), so I'll try that again next.
Really silly question, but how are the terminators set up on the internal bus? What device is terminated, and what position is it on the SCSI cable?
 

Qrani

Active member
Really silly question, but how are the terminators set up on the internal bus? What device is terminated, and what position is it on the SCSI cable?
There's three connectors on the cable (not including the connector to the motherboard). The first from the motherboard is the CD-ROM, the second has nothing plugged in, and the third has a terminator connected.
 

Phipli

Well-known member
There's three connectors on the cable (not including the connector to the motherboard). The first from the motherboard is the CD-ROM, the second has nothing plugged in, and the third has a terminator connected.
Sounds good. Termination disabled on the CD and HD?
 

Phipli

Well-known member
Well there's no HD and I just checked, the CD-ROM has termination enabled
Ah, you'll want to remove the terminator on the third connector or remove the jumper on the CD. You don't want to be double terminating.
 
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