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PM/WS 8500 needs AV module to boot?

belgaonkar

Well-known member
According to this thread, the cpu needs to be firmly seated for the machine to boot: https://68kmla.org/forums/index.php?/topic/21868-8500-wont-chime-need-advice/page-2 

I don't have sound so I'm guessing the CPU card isn't fully seated. This machine is lacking the plastic retainer, so I can't be sure it is in perfectly.

I have tried re-seating the card a million times now with no success. Should the card be touching the plastic notch?

IMG_3130.JPG

I also noticed a slight knick in the cards connector, could something this small be stopping it? I am so stumped right now.

IMG_3135.JPG

 
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unity

Well-known member
That nick, no worries.

But I would seriously clean the motherboard. Dust can, in fact, cause shorts. Properly clean the board. Take a pencil eraser to contacts on that card. Just do some house cleaning and go from there. Just to rule out being something stupid.

I don't know if a good PRAM battery is needed, but I would look into that as well.

 

MJ313

Well-known member
Are you able to discern whether the issue is with the logic board or the cpu card? Do you have a stock 604 cpu from a 75/76/85xx to put in the 8550 and see if it boots?  You could also try the cpu card in another 75/7600 to see what happens. The logic board is *seemingly* stock, so replacing it if it's dead wouldn't be the end of the world. Just some suggestions.

 

belgaonkar

Well-known member
I bought a powermac 8500 logic board and stock processor card. Tried plugging them in today and it boots on the stock parts (obviously). I then tried the Montana CPU with the stock MoBo and nothing happened. The machine doesn't bong, it just spins up. Im guessing that means the cpu card is defective or is not seated properly.

Currently I'm trying to clean the gold contacts on the card. I know I need to use a pencil eraser, but will using isopropyl alcohol also help? Being a dual processor, I fear that it may have over heated; thats probably the worst case scenario. 

 

unity

Well-known member
Alcohol helps in final cleaning. You need something SLIGHTLY abrasive to clean contacts. A "Magic Eraser" also works, or Brillo pad. You just have to be careful.

Don't forget about ROM. If your machine came with a ROM Simm, you may need to carry it over.

 

belgaonkar

Well-known member
Yep, I will try to use a Brillo pad. I did remember to swap out ROMs. My curiosity lead me to removing the heatsink and taking a closer look at the Dual CPUs. Enjoy these pics!

IMG_3229.JPG

IMG_3227.JPG

IMG_3230.JPG

 

unity

Well-known member
You may also want to inspect/compare mobos. While the one that came with the dual cards is a stock part, it may be modified to put out more voltage.

 

belgaonkar

Well-known member
No luck with getting the machine to post. Tried scrubbing the contacts. Ill need to sit down and look closer.

 

belgaonkar

Well-known member
A month later, but no success. I have no idea what I'm doing lol. 

Everything suggested has been tried, it has to be an issue with the card, all other combinations have been tried. Processors don't look visibly damaged, but that doesn't really mean anything.

As mentioned the card does get very very toasty, so maybe it cracked a solder joint? They used the same heatsink as a production machine with one processor and expected it to cool two processors.

Anyone interested in taking a look? Im very skeptical to do this after the last incident.

 

Zippy Zapp

Well-known member
Neat thread.  So if I understand this correct when you put a stock 7500/7600/8500 CPU card in the machine boots?  

You have to love those cases these days, so brittle.  I hope you found better case parts for it. I have an 8100 and the case is falling apart.  Every time I move it something inside breaks.  Ugh, these cases might as well have been made out of potato chips!

 
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belgaonkar

Well-known member
Im home for winter break, and I finally got a chance to look at this old Proto. It booted once and then goes back the issues I was having before. Im 90% confident it needs to be re-flowed to be perfect? Any suggestions for places to get this work done? Not going to risk it and bake the CPU in an oven.

 

belgaonkar

Well-known member
2years later... It's been sitting in the basement and i've decide to take a look at it again. I have all the proto parts back in the machine. I was only ever able get it to post once and that was by fluke. Im gonna start from the beginning. Hopefully it's something stupid like a PRAM battery, but I feel like I would have checked that before.

 

plb007

Active member
Hi, 

I have a working 8500 and a WS8550 that wasn't booting. No chime, just fan and hard disc spin. I thought it was the motherboard because of the battery leak, I found a new MB in perfect condition. No luck, same symptoms. It turns to be the processor card. I put the 8500's processor card and it started. I found 2 cheap processors card and one of them was defective. When processor card is defective, there's no boot chime, just the fan and disc spinning, nothing on screen. I really don't know how to check the processor card outside the computer. I can also assure you that the 8500's doesn't need the AV cable to be plugged in nor the PRAM battery to boot. 

 

Macdrone

Well-known member
processor card would do the trick.  The one you have may be salvageable.  The capacitors could have just gone past the point of doing what they need to do, like every other motherboard of this age these days.  Try a different card, if its posts you will have narrowed the search.

 
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