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486/50 video problem

djin

New Member
Joined
Sep 18, 2005
Messages
1
Location
NC US
I'm having a problem with video on an old 486/50 computer.
After a few minutes (the exact time varies) it will lose color and brightness. The screen will be less than half as bright as normal and all in shades of grey and black instead of colors. I may be able to use the computer for half an hour before the video does this or it may do it in 3 minutes.
Sometimes it will correct itself if I reboot the computer. Sometimes not.
It does this with different monitors attached so it's not the monitor.
It does it with 2 different video cards, one of which worked fine in another computer.
I've tried reseating the video card, but that doesn't seem to be the problem.

I'm thinking it is something to do with the motherboard - maybe a loose connection somewhere. Anyone run into anything like this before? Is it likely to be restricted to a particular slot or is it worth testing each slot separately? I could try a VLB card instead of the ISA card that is currently installed. Testing different slots would involve punching through metal in the back of the case or I'd have done it before now.
 

katey

Member
Joined
Aug 12, 2005
Messages
28
It's not likely to be the system board as all the video generation is controlled from the video card. Does the system do it if just idle or only when you are using it ? My first thought is heat, does the system run very hot ? are you running it with the case off ? hows the fan on the powersupply etc. A quick and easy test is to take off the system case cover and just setup an ordinary household fan to blow into the system therefore keeping it cooler. It's not however adviseable to drop in a bucket of ice :) good luck and keep us posted on your progress.

katey
 

tvdog

Member
Joined
Jul 14, 2005
Messages
17
Re: 486/50 video problem

It could be the timing on the ISA bus. Check the BIOS to see if there is a setting for that and maybe slow it down. A lot of 486's had an option to run the ISA bus above spec to increase the speed of the system overall, but of course you had to have cards that could handle it.

A VLB card will probably solve the problem.
 

Anonymous Coward

Veteran Member
Joined
Aug 11, 2004
Messages
1,544
Location
Shandong, China
Are you running a 486DX-50 or a 486DX/2-50? The DX-50 chips use a 50MHz system bus. If you are using a VLB (VESA) graphics adapter, you will almost certainly run into trouble. VLB is only rated to run at 33MHz. Sometimes you can get away with 40MHz, but 50MHz is almost impossible.
 

vq304

Member
Joined
Sep 25, 2005
Messages
12
Location
Australia
Anonymous Coward said:
Are you running a 486DX-50 or a 486DX/2-50? The DX-50 chips use a 50MHz system bus. If you are using a VLB (VESA) graphics adapter, you will almost certainly run into trouble. VLB is only rated to run at 33MHz. Sometimes you can get away with 40MHz, but 50MHz is almost impossible.

Funnily enough, I've actually got a DX50 here using a VLB video card and VLB IO controller that runs absolutely 100% stable.

Everyone always seems to have trouble getting them to run at 50MHz, mine must be special or something :p (it's definately a DX, not DX2)
 
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