6100/66 is very unstable

[gonzo]

Hello,

I recently got a 6100/66. It is really unstable, it only boots with zapped P-RAM (with fresh battery installed!), sometimes it just does the chime and brings up no picture (as said with a good battery) sometimes it reboots during boot up or even when running Mac OS. I managed to install 9.1 and it run 2 days and after an intended reboot only 10 minutes.

Tried another power supply so far.

Turning it off and on again very fast brings it up too.

Gonzo

 

[unity]

Are there any cards installed?  Have you pulled and re-seated the RAM/VRAM/Etc.? Check for corrosion on the board? Check for leaking capacitors?

 

[Bolle]

The CPU gets really hot in those machines because of bad airflow inside the case.

You might want to check the thermal paste (or the crust that’s left) and apply some new paste.

Also check for caps, corrosion correctly seated cards etc. as unity already said.

 

[Zippy Zapp]

+1 for the CPU thermal paste.  You can also fit a small fan inside the heatsink and connect it to one of the molex connectors.  There was a 3rd party that sold one just for this but any fan that will fit should work.  Also check for leaking caps, as mentioned, as they are starting to fail on this series PowerMac/Performa probably because of the heat inside.  Not a great design for heat dissipation.  

 

[gonzo]

Hello folks,

thanks for the replies.

I removed the PDS expansion, all RAM and the cache module, reseated the ROM module. No SCSI stuff connected. The CPU thermal paste was crap, for the early testing I did not reseat the cooler yet. For sure, I did not operate it for more than a minute.

With a good battery, it powered only on with the quick on/off/on trick.

Could not see a leaking capacitor. The CPU cooling should not be an issue for the power-up behavior.

So what's next? Recapping?

Greetings

Gonzo

 

[Zippy Zapp]

That is weird.  It is acting like the battery is dead as this model requires a good PRAM battery to boot.  I would probably check to make sure the battery socket and connections are good and that the voltage is getting to the board.  I did have one that had a corroded pin on the battery holder and it prevented voltage from getting to the board. I had to remove the holder and solder in a new one and then create a jumper wire to a near by via since the negative side was ruined.  

This doesn't sound like the typical bad cap behavior to me but I am no expert.  Not sure what else to try.

 

[AlpineRaven]

Yep recap before you eliminate any other issues. I have seen quite a few of 6100s in need recap. Even tho they may look ok.

Cheers

AP

 

[trag]

Those early PPC601s can overheat within tens of seconds, so don't try to operate it without the cooler.   Clean off the crusty old heat sink compound and reapply and replace the heat sink.

 

[netfreak]

I've got this exact same problem but I've already recapped my board and put new thermal paste on. With a pram battery, it only turns on the first time and just hangs on every reboot after. I found it easier just to run without the battery. My board seems clean though so I'm not sure.

 

[LaPorta]

What paste would you guys recommend?

 

[trag]

Lots of folks like Arctic Silver V.   However, I've used the little generic tube from Radio Shack without any issues, so I don't think it really matters that much.   You're probably not going to try to overclock the thing to 90 MHz....

 

[Unknown_K]

Generic heatsink compound works fine for me as well as long as you use the correct amount (very little).

 

[jimjimx]

Show pictures of the board. 

Did you check Apple System Profiler?

Is it a really running at 66, or has it been overclocked with a clip oscillator?

And, yes, put a fan into the square part of the heatsink, with the air blowing out to remove heat, not in, to blow air onto the heatsink.