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Crescendo G3 Nubus - VRM blocks PDS cards?

Mr. Ksoft

Well-known member
A while back I salvaged a Crescendo G3 Nubus 215-225/512k from a dead, rusted out Power Mac 8100.  This one of the earlier versions of the card so it is laid out a bit different than the later purple heatsink versions at higher speeds.  I was going to add it to my 6100/60av but it seems that the VRM on the card actually blocks the AV card from fitting.  The card works fine with onboard graphics, but I wanted to keep my AV functionality (and have the choice of using an HPV card later)

I've attached a picture.  Is this normal?  I can't find any large enough photos online to tell if the VRM should be oriented this way.  I thought perhaps it was meant to only be used in a 7100/8100 with the adapter cable (which I don't have...) but I can't find any documentation that supports the idea that the 6100 may need a different version.  The VRM and heatsink is hot glued in place, it might be possible to bend it out of the way or re-solder it at a different orientation (flipped to the other side of the board?), but I was curious if anyone could help me figure out how it's supposed to look.

IMG_20190929_093446_-_Copy.jpg

 
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jessenator

Well-known member
I've seen versions of this upgrade with an orange ribbon connector to bridge to the PDS/HPV card, where the card would sit upright in a bracket socketed into a (sacrificed) nubus slot, just to sit there, not get powered or go through the bus. That's in 71/8100 machines of course.

I wonder if it's just a difference in board revisions/models :/ On some of the aforementioned cards, I've seen "7100/8100 Video Ready" stickers (or some verbiage to that effect) as well as a 6100-specific model. If you look at this manual, it looks like the 6100 doesn't have that protruding bit of population on the board: https://archive.org/details/generalmanual_000022851/page/n9/mode/2up

Edit: here's the 7100/8100 example:
image.png

 
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Mr. Ksoft

Well-known member
Yeah, I don't have that adapter, but it'd be cool if I got a 7100/8100.  But check out the picture you posted... notice anything?  The VRM/heatsink is at a 90 degree angle to mine, and the heatsink fins have been bent out of the way.  Interesting!  I suppose that is a potential solution...

 
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jessenator

Well-known member
I suppose that is a potential solution...
Not a bad idea. I mean if it's just thermal management for that VR, I don't see harm in modifying the heatsink, or swapping it with a comparable replacement.

 
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Mr. Ksoft

Well-known member
Well, I just found out what the hot glue was for!  The regulator was not even connected to the rest of the board-- it was GLUED in place to make contact!  I'm assuming it was some kind of repair job, but really poorly done.  I have no idea how this thing was working.  I'll have to take some additional time to solder it back on... properly.

 

Mr. Ksoft

Well-known member
Bad news.  I think it's dead now.  Whatever was done with the "hot glue fix" shouldn't have been messed with.  While clearing the regulator contacts to re-solder, a glob of the glue took one of the contacts and an SMD cap at position C36 with it.  I attempted to solder them back on, but I don't have the proper equipment to do SMDs right, so of course it doesn't work in the system at all now.  Guess I got greedy thinking I could have an accelerator + PDS.  :-(   Then again, maybe it would have died pretty soon anyway if anything in the glue was disturbed.

On the plus side, it was only the slowest G3 they made for the NuBus machines. I guess I can look for a faster one now. :)

 
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