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8100/100AV Overhaul

LaPorta

Well-known member
Well, now I am getting to what should be one of the easiest, but in one way might be the hardest, refurbishments that I have done.

I have a PowerMac 8100/100AV that I picked up from my college in 2001. Back then, I was a computer science major and had some friends in the lab, one who was the department head. I forget exactly what transpired, but I would up in the basement with him and I noticed thie Power Mac sitting there in basically pristine condition. He said it wasn't used anymore (the thing couldn't have been more than seven years old then). I didn't ask questions and took it. It had a really bizarre isue where it would freeze a few minutes after startup at the desktop (probably why they stopped using it). This happened no matter what disk you started from. So, it sat stored in my parent's basement, unused, until about 2016. After I moved my entire stash to my own place, it sat there until about a year ago when I finally took a look at it. I traced the freezing issue to some bad RAM (I think). I say I think because I am not sure if it was the RAM or some issue with the RAM slots. It works just fine with its soldered 8MB only and the RAM slots empty. That is the part I will have to diagnose at the end.

So, for now, it is just a motherboard, AV card, and power supply recap. The plastics are barely different in color from the metal case, it is amazing. I chalk that up to this thing being climate controlled and in the dark in the school basement as well as my parent's and then my house. I would post photos, but I am still space-capped until that forum issue is sorted out. The only thing that I very stupidly did was forget to take out the AV card when I removed the logic board a second time - SNAP....off came the plastic card retaining clip! They are so thin, glue would just snap it again. I wondered if there was a way to either drill it out and insert a little metal pin to hold it, or support it somehow otherwise.

So, just two questions:

1. - Any suggestions for how best to repair the clip?

2. - Any improvements or add-ons that anyone would suggest for it?

 

Trash80toHP_Mini

NIGHT STALKER
I all boils down to what apps you want to run. More than rudimentary VidCap is a non-starter on that machine. VideoVision Studio and HPV-2/4MB would be my notion for VidCapif you throw SCSI2SDv6 on its fast bus if you haven't got JackHammer or the like and the drives for it? Gaming or PhotoShop would be entirely different.

 

LaPorta

Well-known member
So I finished the whole power supply and logic board recap. Reassembled everything. Fired up the machine and it was good to go. Started up, no problems. Saw that my newly-installed 64 MB of RAM was recognized without issue. Figured I'd play some Marathon. Fire up Marathon, and just as the program starts to load, the entire machine shuts down, power and all. So, I attempt to start it again from the keyboard. Machine starts, HD spins up, get half a startup chime, and then off again. The more I try this, the shorter time from start to off until it doesn't start at all. So, I disconnect from power. Try a logic board reset. This does not help. However, the longer I keep it unplugged, the more it seems to be able to stay on for longer before turning right off and then shorter and shorter time until shutting off.

Sounds to me like perhaps there is some issue with a power supply capacitor I replaced. But, why would running a program trigger that? How come it ran just fine until that point? Was it just coincidental timing? Any suggestions for what to try next?

As a side note, most times even if it won't turn on, the power supply makes a click after pressing the power button, but then there is an immediate second click and it doesn't turn on.

 
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jeremywork

Well-known member
The more I try this, the shorter time from start to off until it doesn't start at all. So, I disconnect from power. Try a logic board reset. This does not help. However, the longer I keep it unplugged, the more it seems to be able to stay on for longer before turning right off and then shorter and shorter time until shutting off.
I have a IIci that behaves identically to this. I haven't recapped the board yet but I did try another PSU and the symptom didn't change, so at least in my case I suspect a capacitor in the power button circuit is to blame (as the behavior could probably be replicated by pressing the rear case power button at closer intervals manually on a healthy system.)

Conversely, my IIfx has started popping up the 'Safe to switch off your Macintosh now' screen when I choose Shutdown, though if I leave it on long enough for all the electronics to reach operating temp and then choose shut down, it happily shuts down. Some old caps return to proper tolerance after warmup while others drift out of tolerance it seems.

This might be useful:






 
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LaPorta

Well-known member
Thank you for that. I did some more testing: I can currently jump-start it by shorting pins 12 and 21 per what some said to complete the power on circuit from 5v trickle current. Once it starts up, I verified voltages: good +5 on the +5 lines, -12 on the line where it should be. All voltages completely within spec. Fan turns nicely, no issue. After about 30-45 seconds, the unit just shuts itself off, no explanation. Voltages disappear, but +5 on the trickle line I still present. Not sure what would make this just cut off like that.

 

LaPorta

Well-known member
This gets even weirder still. I now think something is wrong with the logic board. I reconnected the power supply to the logic board. To my complete and utter amazement...the thing actually started up. Thinking maybe it was a load issue, I hooked it up to the HD as well. What would you know, the HD ran as well. However, the machine froze on startup. Restarted with extensions off. Got to the desktop. Fired up Marathon, and yet again the very instant it would have gotten to where it would have played the opening screen, the whole machine shut down. Couldn't start it up again, just kept turning on, then off. It cannot be a coincidence that this happens at precisely the same time. Sound usually plays at that point in the game startup: is there any way that does anything? I replaced all of the capacitors on the logic board.

I think this is one for the books: it makes no sense whatsoever, but shows a predictable pattern!

For completeness sake, I must say that I also recapped the video card. That could also have issues to do with this potentially.

 
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trag

Well-known member
@LaPortaHave you cleaned and replaced the heat sink grease on the PPC601 CPU?   I've seen similar issues on 7100s.  The heat sink grease had turned to chalk.   Had me scratching my head, reading to start pulling out chunks of hair, until, once, I noticed video artifacts before freeze up.   The artifacts reminded me of an overheating symptom.

Replaced the heat sink grease and it was perfect after that.

 
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jeremywork

Well-known member
Thinking of what resources might be called the moment it would play the opening...

I agree that these need new thermal grease after so many years.

When you startup with extensions and freeze, do you get a dialogue if you try Cmd+Opt+Esc? Installing Macsbug would give more technical details but that can sometimes be useful if it reveals the name of the hung process.

Does the machine pass Apple's RAM test in Personal Diagnostics/Mactest Pro?

If not that, check to see that it can enter any resolution or color mode it may be trying to select when launching Marathon, that it can play sound properly.

 
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LaPorta

Well-known member
Well, I will try an dsee how long I can get the thing to stay on for. Hopefully, now, over night, it will not shut off right when I press the power key! The issue is once that shutdown happens, time is needed befrore it will even start again. I can replace the grease and see. The thing is, until I did the recap, this never had such power issues before. It had other freezing issues, but never related to the machine shutting itself down. That said, I can also see if just playing a sound in general causes the shut down.

I supose maybe two other thngs are possible: 1. Maybe the thermal seosnr was damaged by me (not sure how, I didn't touch it), or 2. Maybe now it IS working and sensing the heat after the recap.

 
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LaPorta

Well-known member
Ok, so I did a few more tests. I am now 100% sure that the power issue is the supply itself. Two things: I replaced the thermal compound on the motherboard, this didn't help any. I popped in a spare 8100 motherboard I have instead, and the exact same thing happens. I don't know if there is some short or something else going on inside the power supply, but it seems more and more like it. Remember, this did NOT happen prior to my recap, so I probably caused it. The machine has always been prone to freezing and crashing, but that is a separate issue that never caused it to shut down.

Guess I am relegated to hunting and pecking in the power supply now....ugh. Anyone have any ideas why it would just shut off?

 

paws

Well-known member
I don't have any input except that if it's not temperature-related, it could be an error in the soft power circuitry. There's some sort of relay in there, and possibly a flip-flop that controls it.

Mostly I'd just like to thank you for documenting your troubleshooting. It's very useful to have reports like this on weird symptoms.

 

LaPorta

Well-known member
Im resoldering all of my cap work. I also reflowed some ground pads that didn’t look great. It makes me think there’s a bad connection somewhere that gets throw off when it heats up. Tomorrow I have to work overnight, so I won’t realistically get back to this till Tuesday.

 
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LaPorta

Well-known member
So, I remembered that about a year ago at a massive free haul, my brother picked up a random, massive power supply. He just thought it looked cool and stuffed it in his closet.

Fast forward to my troubleshooting. I start thinking about it. He does too. What does he happen to have in his closet?

A PowerMac 8100 power supply.

So, I got it from his house today and tried it. Power issue is non-existent. It is something I messed up with the power supply. So, I am concentrating there, checking my work.

 

demik

Well-known member
Good luck with those PSUs. Asteks on 8100 and knew to not be the best ever made. 

Mine exploded and killed the motherboard with it (hole in the motherboard). Another user around here had a similar issue. I would suggest an ATX conversion after you get everything sorted out.

 

macuserman

Well-known member
@LaPorta Do you happen to have handy the list of caps you replaced on the 8100 MB? I have one that doesn't want to start up for me and for lack of any better ideas I might start with replacing the caps.
 

trag

Well-known member
This space intentionally left blank.

I thought there was a way to delete one's messages...
 
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