Gootsey wrote:

Hey all, thought I was gonna upgrade my PC today but got a little thrown off track. […]
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Hey all, thought I was gonna upgrade my PC today but got a little thrown off track.

I've got an IBM PS/1 Consultant 2155-G54. I grew up with Windows 98 and a Celeron, so anything before that is pretty unexplored by me. I bought a 486DX2-66 Overdrive before and found out that was incompatible due to the bus speeds and yadayada, so I picked up a 486DX4-75 still in the original box on eBay.

I popped it in the second I got it, it booted (Hooray! No video output with the DX2-66) annnd that's it. After boot it's stuck on the POST screen with error 129 which, as far as I can find out means "Processor Changed" but it can't configure it correctly. I also can't get into the BIOS unless I remove the OverDrive from the upgrade socket and use the 486SX-25 that's soldered on.

I found this article which is for a totally different system but I think it's the same problem,
http://ps-2.kev009.com/pcpartnerinfo/ctstips/9612.htm
the reason being "this processor has a 16K internal cache and the BIOS only supports 8K". I can boot into the BIOS with the OverDrive removed and confirm that it displays 8K of cache.

Please tell me that there's a way around this roadblock and that I'm not $50+ in the hole already and still haven't found a working upgrade!
Thanks All. 😀

It looks like you need a BIOS update if there is one to get the Intel DX4 Overdrive working, otherwise you can try an AMD DX4 "NV8T" as those are more compatible. The AMD chip needs 3.45V and your motherboard probably only supports 5V. The AMD chip will likely survive for years at 5V so I would give it a try as the voltage converter boards and upgrade chips with included VRMs are expensive as you already noticed. If you try to run at 3.45V chip at 5V make sure you use a heat sink with fan.