Overdrive DX-4 100Mhz unstable \ VOGONS

Overdrive DX-4 100Mhz unstable

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First post, by 386SX

Posted on 2017-06-22, 15:30

386SX Offline

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Joined: 2014-10-27, 12:56

Hi.

I got this mainboard (ADI?) TK8498F/GP 4N D24 with UMC 8498F chipset and in perfect state and it runs flawless with the ram I have (various 60ns and also one 16Mb 50ns one) with the DX2-66 cpu (Overdrive). The problems come with the Overdrive DX4 100Mhz I have that when installed is detected as DX-4-S 120Mhz cpu (?) running at 100Mhz correctly but games often crash with it, no matter the ram I use. It's not an heat problem cause I've a fan running on it.
Doom crash in timedemo randomly for example. There're many jumpers and I tried various config and it still recognized as above and nothing change.
Any advice to solve this?
Thank

Reply 1 of 3, by Deksor

Posted on 2017-06-22, 17:37

Deksor Offline

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Maybe try to update the BIOS if you can. My AP43 board was hanging at POST when I installed my 5x86 with the 4x multiplier set. However with the 3x multiplier it worked flawlessly. The bios was from august 1995 and the 5x86 was released only few month later. I updated the board with a bios from 1996 and then it works perfectly.

Maybe also since your previous CPU was a DX2 overdrive, it probably had write-back cache instead of write-through so maybe you board still tries to use the cache as write-back even though you DX4 might not support this mode. However I'm not sure that if this was true the computer would even boot so this might not be the problem

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Reply 2 of 3, by Ampera

Posted on 2017-06-23, 06:41

Ampera Offline

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Joined: 2016-11-16, 22:31

If it detects it as a 120Mhz CPU, then overclock the CPU to 120Mhz. Most DX4-100s can run up to 120Mhz no sweat. Just ensure you have adequate cooling.

Reply 3 of 3, by 386SX

Posted on 2017-06-23, 13:14

386SX Offline

Rank l33t

Rank: l33t
Posts: 3141
Joined: 2014-10-27, 12:56

Deksor wrote:
Maybe try to update the BIOS if you can. My AP43 board was hanging at POST when I installed my 5x86 with the 4x multiplier set. However with the 3x multiplier it worked flawlessly. The bios was from august 1995 and the 5x86 was released only few month later. I updated the board with a bios from 1996 and then it works perfectly.

Maybe also since your previous CPU was a DX2 overdrive, it probably had write-back cache instead of write-through so maybe you board still tries to use the cache as write-back even though you DX4 might not support this mode. However I'm not sure that if this was true the computer would even boot so this might not be the problem

Problem with the bios is that I don't know if one exist. Even the brand of this mainboard is not sure.

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