Figuring out dead PowerMac 6100

[netfreak]

Have you looked under the heat sink?   Every 7100 I've had my hands on needed its heat sink paste cleaned off and replaced.   I don't know why the 8100s and 6100s didn't but that was 15 years ago.   I imagine all the NuBus PowerMacs need their heat sink paste replaced by now.  Still, you would get a good start up bong if the problem was just bad paste.  Bong and then immediately overheat...

So, look under the heat sink and check whether the CPU is cracked.  It's usually possible to tell by eyeball.

I had looked under the heatsink before and the CPU did not look like it was cracked, and after my recap I also cleaned the CPU to add more heatsink compound. I've been super careful with the heatsink but I suppose something may still have broken at some point. I have a spare board with the exact same symptoms and the CPU looked OK on that one too. Now I'm not sure if I have two faulty boards or two faulty power supplies or who knows.

 

[trag]

This is the kind of thing that having a local club was good for back in the old days.    Then you could just find a fellow member with a 6100 or compatible power supply and test it.   

If I had to guess between two bad power supplies and two bad logic boards, especially after a recap, I'd guess power supplies.  

Also, are you certain you have the correct ROM module?  I can't remember the part number off the top of my head unfortunately.  I have it written in a lab book at home.   I ask because the form factor is the same as for the entire X500/X600 PCI PowerMac series (although most of those had soldered ROM) and also the same as the Beige G3 ROM.  A little Googling suggests that Apple 341-0741 is the correct part.  I think the 0757 will also work though.

 

[IIfx]

Idea: Contact Cleaner.  CRC QD from an auto parts store works wonders.

I have had that stuff fix inexplicable problems. Spray down the RAM SIMM slots, ROM slot, and cache slot. Heck, just bathe the whole board in the stuff, it evaporates.

 

[netfreak]

This is the kind of thing that having a local club was good for back in the old days.    Then you could just find a fellow member with a 6100 or compatible power supply and test it.   

If I had to guess between two bad power supplies and two bad logic boards, especially after a recap, I'd guess power supplies.  

Also, are you certain you have the correct ROM module?  I can't remember the part number off the top of my head unfortunately.  I have it written in a lab book at home.   I ask because the form factor is the same as for the entire X500/X600 PCI PowerMac series (although most of those had soldered ROM) and also the same as the Beige G3 ROM.  A little Googling suggests that Apple 341-0741 is the correct part.  I think the 0757 will also work though.

Yeah I've got two power supplies and I opened one of them without seeing any OBVIOUS problems... The ROM and L2 chips in there now are what was in there when the system used to work. I did get another ROM on ebay and remove the L2 chip but nothing changed. Symptoms unfortunately point to broken CPU, but it really didn't look broken.

Idea: Contact Cleaner.  CRC QD from an auto parts store works wonders.

I have had that stuff fix inexplicable problems. Spray down the RAM SIMM slots, ROM slot, and cache slot. Heck, just bathe the whole board in the stuff, it evaporates.

Actually yes I will be trying something like this, or potentially more absurd like a run in the dishwasher. I dishwashed my LC board for fun when it was completely dead and works just fine now.

 

[netfreak]

Had a 6100/60 board come in from ebay and it works fine with the rest of my original parts. I guess that means I've got two boards with dead CPUs. Sigh.

EDIT: yeah I just popped the heatsink off this one to put new compound on it... it looks much different on the working CPU than my head ones... they're clearly fried.

 

[trag]

Idea: Contact Cleaner.  CRC QD from an auto parts store works wonders.

I have had that stuff fix inexplicable problems. Spray down the RAM SIMM slots, ROM slot, and cache slot. Heck, just bathe the whole board in the stuff, it evaporates.

Is that the one that is tetrachloroethylene (causes cancer, but only in California)?

I ask because I have a couple of cans of brake cleaner left over, and while I was at the auto parts store I noticed that the can of Contact Cleaner from the same brand, was exactly the same size, and had exactly the same ingredient list (just the tClC2H4) as the brake cleaner but cost about $3 more. 

 

[trag]

Had a 6100/60 board come in from ebay and it works fine with the rest of my original parts. I guess that means I've got two boards with dead CPUs. Sigh.

EDIT: yeah I just popped the heatsink off this one to put new compound on it... it looks much different on the working CPU than my head ones... they're clearly fried.

That's bad news, but don't throw the boards away.   Even if you decide to get rid of them, they may still be useful to someone for parts.   I think I've seen new/unused PPC601 chips on Ebay for under $30.    Heck of a soldering job  though.

 

[netfreak]

That's bad news, but don't throw the boards away.   Even if you decide to get rid of them, they may still be useful to someone for parts.   I think I've seen new/unused PPC601 chips on Ebay for under $30.    Heck of a soldering job  though.

Yeah I'm not going to toss the boards. One board I already pulled some other caps off for future use. May also pull other chips off. I was actually looking on ebay for CPUs but ones that ship to Canada were still more than I'd want to pay.. Plus there's no guarantee I could ever manage to solder that in.

 

[netfreak]

I have a followup I can't seem to figure out... It SEEMS that my pram corrupts itself and doing a soft reboot of the computer will often result in the system doing nothing and showing a blank screen. Even after additional reboots and power cycles I can only fix it by pulling the pram battery (new) and waiting for it to zap itself. I just pulled the battery entirely and double-tap the power instead of dealing with constantly opening the case, but I think whatever the issue is happens to make my DOS card not show up most of the time.

Any potential ideas? I'm running 7.1.2 and won't be changing the OS version.

 

[jimjimx]

I've never run into a power Mac that needed caps, hope this isn't the start of them.

All caps will go bad, maybe with the exception of ceramic......

They are supposed to block DC, but after time, they will allow it through, turning it into a resistor. 

When it does this, it is called a leaky capacitor, because it is leaking DC.

.... Not only electrolyte fluid leaks!