Author Topic: Vertical bars on PM8500 Display  (Read 181 times)

Offline rshaw

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Vertical bars on PM8500 Display
« on: July 04, 2018, 09:37:23 PM »
Hi,
Recently I pulled out of storage a PowerMac 8500 that hadn't been operated in years.
After opening the case and shaking out bits of broken plastic, and reseating cards,
a first power-on attempt didn't give a chime.  But after ctl-command-power it started right up.
The good news is it has a 1 GHz PowerLogix G3 card, and 1 GB of memory.
The bad news is that there are vertical bars on the display, very apparent with 256 colors,
apparent with thousands of colors, and a good display with millions of colors.

Any suggestions about how to fix this?  Also, the NTSC out doesn't work, but I think I have
several of those 8500/8600 AV cards somewhere.

Thanks!
rob

Offline Astroman

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Re: Vertical bars on PM8500 Display
« Reply #1 on: July 05, 2018, 02:10:38 PM »
didn't these Macs have video RAM installed in special Simm-slots ?
Reseating those may help... fingers crossed.

Offline rshaw

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Re: Vertical bars on PM8500 Display
« Reply #2 on: July 06, 2018, 12:28:25 AM »
Yes, thanks, there are VRAM slots.  But something marginal is going on, the 8500 started hanging during boot,
just after all the desktop icons were rendered, and one time dropped into a debugger.  This might have to do
with the much-needed rain we had this afternoon in this dry part of the country.  So the question is, get
a really fast 8500 going, but maybe at the cost of tracking down obscure faults in 20 year-old hardware...
But it is a cool machine!

Offline Astroman

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Re: Vertical bars on PM8500 Display
« Reply #3 on: July 07, 2018, 01:44:07 AM »
increased moisture may in fact have influence on (partly) corroded contacts.
Use pure alcohol (from the pharmacy) to clean contacts on Simms (simple).
The counterpart on board is more difficult, alcohol soaked cardboard or similiar may work.
Check the board for capacitors leaking, they are the most common part to wear out over time.

Offline Irisman

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Re: Vertical bars on PM8500 Display
« Reply #4 on: July 07, 2018, 04:17:28 PM »
Yes, alcohol is good for cleaning memory contacts. Isopropylic alcohol around 99% (pharmacy available) is the best due to complete evaporation without residues.

For other electrical contact cleanings and soft rusts, I found that the Deoxit D5 is a magic tool (bit expensive, but really effective).

Offline rshaw

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Re: Vertical bars on PM8500 Display
« Reply #5 on: July 11, 2018, 11:55:25 PM »
Thanks, I located the VRAM chips, took them out and cleaned the contacts with alcohol and q-tips.
It definitely changed the behavior, then there was a vertical bar that followed the cursor around.
There were four chips, so I swapped the "bank 1" and "bank 2" chips, and now the display is perfect.
The bad chip is now in the upper address space, which is probably for the NTSC display, which doesn't work anyway.

The interior plastic of the 8500 completely crumbles, which makes me nervous about taking it apart.
But there's a firewire PCI card, and a "Neptune" disk, which transfers at over 30 MB/sec.  So the next project
is to find Final Cut Pro 3, and a DV camera, and edit like it's 1998.

Obsolete?  These days, that's a compliment.

Offline Irisman

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Re: Vertical bars on PM8500 Display
« Reply #6 on: July 13, 2018, 02:23:55 AM »

Obsolete?  These days, that's a compliment.

I still keep my Echo Gina PCI audio card.... still working!