Author Topic: Powermac 8600 Display Problem  (Read 2310 times)

Offline Mardeec

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Powermac 8600 Display Problem
« on: March 03, 2019, 03:15:20 PM »
Any ideas on what’s causing a grid of blue dots (see attached) to appear across the entire screen?

I’m using a Samsung SyncMaster 730B LCD monitor with a Belkin Mac to VGA Monitor Adapter (F3H1381).  This set up was working perfectly until last time I was setting up the computer and thought I had everything plugged in.  Duh, I forgot to connect the monitor to the computer, and so I plugged in the cable w/o shutting down the computer.  Just as I was thinking “maybe I shouldn’t have done that,” the blue dots appeared, and have been there ever since.  Everything functions normally except for the dots.

When I connect a TV to the computer’s composite video out, the dots are not present.  I’ve tested the monitor with other computers and the dots are not present.  When I take a screenshot, the dots are not present in the saved image. 

Powermac 8600/250 with Sonnet Crescendo G3 500 processor, OS 9.1, 512Mb RAM. It has the “stock” video which is part of the motherboard.  I don’t have any original software. I do have the original processor.

Did “hot plugging” the monitor have anything to do with this?  If so, could I add a video card? The computer has 2 open PCI slots.

Thanks for any light you can shed on this problem.

Offline Astroman

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Re: Powermac 8600 Display Problem
« Reply #1 on: March 03, 2019, 11:59:19 PM »
Set the adapter to a different resolution that your monitor supports, reboot.
Then set it back to the intended resolution and reboot again (both times with monitor connected). It should then fall back to the proper sync rate.
The blue dots are part of the image buffer that get replicated in a pattern over the screen if the data to display rate doesn't match.

Offline Mardeec

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Re: Powermac 8600 Display Problem
« Reply #2 on: March 04, 2019, 08:36:28 AM »
Astroman, thanks for your reply.  Before I start this procedure, I wanted to check to make sure I understand the steps.

On the Belkin adapter, I’ve been using the VGA/SVGA setting in Mode 5 with switches 2367 turned on.  According to the Belkin chart (attached), this would support resolutions of 640x480 and 800x600 @ 60Hz.  Are you suggesting I change to another switch setting?  For example, setting the switches at 1367 would support a resolution of 832x624, which my monitor also supports. 

I was under the impression that the adapter had more to do with pin connections that resolutions, but maybe that’s not accurate.

Thanks again!

Marty

Offline Astroman

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Re: Powermac 8600 Display Problem
« Reply #3 on: March 04, 2019, 12:04:23 PM »
The adapter's dip switches set a number of bridge connections on the Apple side of display connector - this was the method to identify monitor type and resolution.
(most screens of that period had fixed resolution, multi-sync as used today had just started... and those displays were quite expensive)
Some switches may handle sync signals, as there were several sync modes depending on model/manufacturer.

I don't remember how settings were stored back then - it may help to power down the Mac, disconnect the power cord and switch the unplugged Mac on/off a couple of times.
This unloads the capacitors on board. The plug in the power line and reboot.
It's a procedure known to magically cure a lot of errors on very old Macs if something happened to be stuck in RAM.

If you have 2 resolutions availabe, switching between them via monitor control panel might work as well.

Offline Mardeec

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Re: Powermac 8600 Display Problem
« Reply #4 on: March 06, 2019, 08:18:18 AM »
Astroman, thanks for your insight on this issue.  Here’s what I’ve tried so far:

-Select different resolution in monitor control panel, reboot, select original resolution in monitor control panel, reboot.
-Select different switch setting in adapter (1267), reboot, select original switch setting (2367), reboot.

In both cases, the dots are still present.

In cases where there is no display at all, the computer’s manual suggests resetting the PRAM and NVRAM with these steps:
•   Turn on
•   At the startup sound, press and hold Command Option P R
•   When the startup sound repeats twice, release keys, and press and hold Shift
•   Release key when “Extensions Off” appears
•   Open Systems folder, open Preferences folder, drag Display Preferences to Trash.
•   Restart.

I tried this, but no change.

I understand this computer has a CUDA switch which can be reset.  Do you think this is worth a try?  I read somewhere online it’s necessary to hold this switch down for 20 seconds, but I wanted to get another opinion before I try it.

Would it be worth a try to reseat the RAM and video RAM sticks?

Thanks for your help!  I’m not ready to give up!

Marty

Offline refinery

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Re: Powermac 8600 Display Problem
« Reply #5 on: March 06, 2019, 01:59:03 PM »
can you replace the adapter, or the cable? probably a much more likely component to fail versus vram, or a video card.
G4/MDD 1.42 (9), G4/GB 500DP (X), Beige G3 400 (upgraded) (9), PBG4Ti 1Ghz (X), PBG3WS 300 (9)

got my mind on my scsi and my scsi on my mind

Offline Astroman

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Re: Powermac 8600 Display Problem
« Reply #6 on: March 06, 2019, 02:37:22 PM »
If different settings didn't change the dots then display buffer and memory are the main suspects. Reseating modules is a good idea and you may clean the contact area with pure alcohol.
For the 'slot contacts' use a piece of cardboard (a bit thinner than the Dimm to get in easier)
But usually the plug out and back in is enough. If you see a different pattern then it points even more to memory.

Offline FdB

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Re: Powermac 8600 Display Problem
« Reply #7 on: March 06, 2019, 04:29:09 PM »
Hey Mardeec,

PM me your address and I’ll send you this ViewSonic adapter
to try. If it works for you… great! You’ll owe me a postcard.
If not? Well, then… nothing. ;)
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Offline Mardeec

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Re: Powermac 8600 Display Problem
« Reply #8 on: March 07, 2019, 12:23:40 PM »
I was able to test the VGA cable with another computer and make sure it's ok, but I don't have another 15 pin Mac I can use to test the adapter.  Fury, thanks for your offer of the ViewSonic adapater, and I sent you a PM with my address.

I'll get to work on cleaning and resetting the memory modules.  I was given this computer, and it appears it's been stored in dusty conditions, so it needs a good cleaning anyway.

I'm mad at myself for "hot plugging" the video cable and adapter, and that seems to be the event that started the problem.  Thanks to everyone for helping me recover!


Offline Mardeec

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Re: Powermac 8600 Display Problem
« Reply #9 on: March 08, 2019, 02:37:42 PM »
Thanks to Fury and his super efficient postmistress, the adapters were delivered today, but no change.  I've confirmed that my monitor uses "separate horizontal and vertical sync," so that helps in getting the proper switch settings on the adapters.

I'll try reseating the memory modules, booting from a CD, and hope for the best.   

Offline FdB

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Re: Powermac 8600 Display Problem
« Reply #10 on: March 12, 2019, 11:03:31 AM »
Reference:
https://en.wikipedia.org/wiki/Integrated_Micro_Solutions

Attached images: Earlier Version - Later Version - Manual Pages
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Offline Mardeec

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Re: Powermac 8600 Display Problem
« Reply #11 on: March 12, 2019, 12:12:54 PM »
No luck with reseating the memory modules, booting from a CD, and trying another adapter.

Enormous thanks to Fury for sending me an IXMicro 128 video card from a PowerMac 9600 to try.  At this point, it seems safe to conclude that (1) hot plugging the video cable caused some damage to the internal video and (2) the only hope for this computer is an external video card. 

The card Fury sent me has the IXMicro Twin Turbo 128-3D chip.  Everymac.com indicates the PowerMac 9600 came with a Twin Turbo 128 card.  OWC lists several drivers for "Twin Turbo 128" cards, and the manual I found (attached) indicates 3 different models of Twin Turbo 128 cards (Twin Turbo-128M, M2, or M8).

Drivers at OWC: https://eshop.macsales.com/tech_center/index.cfm?page=other_ixmicro.html&title=Other%20%7C%20IXMicro

Offline Syntho

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Re: Powermac 8600 Display Problem
« Reply #12 on: March 12, 2019, 06:55:26 PM »
There are multiple versions of the stock 9600 video cards. Usually in two categories: the long board version and the short board version. You've got the long one, right? The Mac OS Installer will put the correct version in your extensions, and yes, the extensions for the long and short board are actually different. The easiest way to get the driver is to have the video card in your Mac, then do a fresh install of 7.6.1-9.2.2. Any will do. That will get you the correct driver. If you have to, use an external drive or create a partition and do a fresh install of any of those OS's. Drag the driver from that new install and save it somewhere, then switch it out on your main install.

I do have those drivers laying around, but there is a potential problem: you have an 8600 as to where my 9600 is... a 9600. The extension is called '9600 graphics accelerator'. When you do an install, it'll probably be called 8600 graphics accelerator. It'll take you more time to do an install to snatch the drivers, but better to spend 45 minutes doing that to get the exact ones than to use something that might not work, or work as well.

Offline Syntho

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Re: Powermac 8600 Display Problem
« Reply #13 on: March 12, 2019, 06:57:24 PM »
Also, is that card FdB sent an actual dual monitor card? Does it have two jacks on the back of it, or just one?

Offline Syntho

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Re: Powermac 8600 Display Problem
« Reply #14 on: March 12, 2019, 07:09:03 PM »
By the way, you don't even need the drivers to get it to 'work' and see if that clears up the problem. The video won't look good and it'll be slower and all of that without the right drivers, but the blue dots should have disappeared when you popped in that IXMicro card. Even booting from a CD with the card in there will suffice. Can you confirm that the problem disappears simply by using the IXMicro? If it does clear up the major blue dot problem when you boot, then try to do the fresh install and you'll be good to go. More work than you might want to do, but it's definitely for the best. If it isn't clearing it up, I have no idea what it could be.

Offline FdB

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Re: Powermac 8600 Display Problem
« Reply #15 on: March 12, 2019, 07:40:25 PM »
Thanks Syntho!
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Offline Mardeec

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Re: Powermac 8600 Display Problem
« Reply #16 on: March 13, 2019, 07:54:25 AM »
Syntho, thanks so much for your guidance.  Yes, the card Fury sent me is a long one, and it's a dual monitor.  And yes, when I boot with the card in place and a monitor connected to the card,  I don't see any blue dots.  The computer was noticeably slower, but I'll do a full OS install as you suggest to get the proper driver.  This will require installing the original processor for the OS install, then run the Sonnet installer, then pop the Sonnet processor back in, but at least there's plenty of room to work in this computer.

Fury, thank you again for the card.  That was really the key in fixing this problem.