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What are some common causes of an 8100/100 just not powering on?


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Hi,

 

I've recently purchased an 8100/100 that's in pretty good cosmetic shape (we'll see if that persists in being true once it arrives), but the previous owner said it has an issue where it appears to not power on. The obvious suspect is a failed PSU, but I'm curious of there are other trivial perhaps less insidious things with an 8100 that can exhibit similar behavior?

 

Thanks!

 

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On 3/18/2021 at 4:57 AM, Nathan_A said:

The obvious suspect is a failed PSU, but I'm curious of there are other trivial perhaps less insidious things with an 8100 that can exhibit similar behavior?

 

 

There are several reasons why a Mac doesn't power on. I usually use some sort of incremental search for the source of failure starting with very simple diagnostics like a visual check.

 

What does happen when you power on the machine? Do you hear any noise (PSU fan spinning, HDD spinning and clicking)?

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  • 68kMLA Supporter

Could be the PSU (as in my case), or possibly even logic board issues. With the soft power on circuit, if the motherboard is not working properly for whatever reason (power circuit degraded, etc), then the power supply won't turn on at all to begin with. One thing you can do if you get no noise, fan, etc, is to plug the PSU in, have the connector to the logic board unplugged, and measure the yellow wire with a multimeter for volts DC to ground. That wire should be carrying a +5v trickle current to enable the soft power on circuit. If even that is not present, it is the PSU. If it is, that doesn't rule out the PSU entirely, but would also make the logic board potentially suspect.

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  • 2 weeks later...
Posted (edited)

Sorry it took me a bit to get back to this topic. I didn't have the 8100/100 in my possession yet. It arrived... mostly intact. There are several small pieces of plastic that I need to figure out where they came from and try to super glue them back into place. The battery doesn't appear to have exploded, which is nice. So I can replace that easily enough. The biggest problem with what happened during shipping was that the HPV card an the Nubus Ethernet card came unseated (I'll never understand why Nubus had no retention mechanism like ISA, VLB, PCI, etc. :?:) and were rattling around inside the case. Though miraculously they didn't act like the live grenade in there that I'd feared they might when I first realized what happened.

 

Got one big time bonus from the machine (which needs all its case plastics carefully cleaned)... I saw the HPV card floating around in there and it had "Visiontek" SIMMs in the VRAM slots. All totaled its 8 chips on 4 SIMMs, the part# is OKI M548262-70, which from what I can tell makes each SIMM a 512k VRAM SIMM... meaning this thing is the rare specimen of a 4MB VRAM Apple HPV card! :-) Even if I can't get the machine working, that alone is almost worth the money I spent on it. It also has two... yes two... Apple SCSI HDDs. The first is a Quantum sourced 500MB drive and the second is an IBM sourced 1GB drive. Last, but not least it also came with a DaynaPORT BlueStreak 10/100Base-T Nubus Ethernet card!

 

I haven't been able to get the danged motherboard out of it safely yet (this Quadra 800/840 & PM 8100 case design is truly and utterly ridiculous for servicing/upgrading), so I haven't figured out how much RAM it has or how big the L2 cache module is.

 

The shield for the floppy disk drive is super rusty, but I don't know if that's also impacted the drive itself. The bottom metal pan of the machine also has some rust. As well as the rear panel predominantly around the powersupply venting. It makes me think the thing was used in a coastal/humid environment.

 

As for the primary problem with the machine right now (i.e. not powering up), the machine does nothing when I plug it into power and press the power button. No clicks. No fan movement. Not so much as a twitch or a twinge. I set my multi-meter to DC volts, and touched the red probe to the yellow pin and the black probe to a black pin, nothing registered. So it seems like the trickle power for the soft-on/off function isn't making it through the PSU at all?

Edited by Nathan_A
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I'd pull out the PSU, disconnect all devices attached to it and check the voltages then. What part number do you see on the PSU? It's sometimes possible to find the schematics for some PSUs used in the old Apple machines. BTW, I successfully fixed and recapped an ASTEC PSU in my PowerMac 6100 three years ago...

Edited by powermax
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  • 2 weeks later...
  • 68kMLA Supporter

Trust me, I am still working on my 8100, through two power supplies. Have two good working motherboards thankfully, just finishing the darn power supply.

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  • 3 weeks later...

Well, good news. I acquired a spare power supply and when I plug it in and connect it to the mainboard the soft-power switch causes the PSU fan to start spinning. That's more than I could get to happen with the original PSU.

 

I still haven't put the whole machine back together yet to see if everything functions or not because I have about two-dozen pieces of small plastic I need to figure out where they came from and whether or not I can super glue then back in place. So, that might be tonight's project.

 

One thing that's weird with this machine is that the heatsink has a peltier junction between the CPU and the heatsink. I literally cannot believe Apple used such a thing in a stock machine. The cold side will get really cold, which is great, but the hot side will get really hot, which is less great if you can't vent off the heat efficiently. In the case of the 8100 they still use the horrible cage-style heatsink, which I'm sure gets thermally saturated by the peltier very quickly, and to compensate for this the CPU sits directly below the huge PSU fan.

 

The problem with this of course is that all that excess heat generated by the peltier junction is being pulled through the PSU, which can't possibly be great for their longevity relative to say the same PSU in a Quadra 840AV or an 8100/110 (assuming the 110 is a 601+ instead of a 601).

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Put the machine all back together with the new PSU and she fired right up and booted into an install of OS 9 that the previous owner must have been running. It's basically a clean install except for having WeaveMaker Pro on it.

 

Pretty cool vintage workstation. 8-)

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