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HP Vectra 486/25NI - Enable Pentium Overdrive support?

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First post, by bc732

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Hi all,
I've been working on my HP Vectra 486/25NI, and am trying to upgrade the processor as far as I can.
As far as I can tell, the "NI" series is the same as the N-series but with integrated ethernet.
It came stock with a 486SX-25, and I currently have a DX2-66 in it.

I managed to get an 83mhz Pentium Overdrive (109X4405H6J05,) but the machine will not boot with it inserted. I am not 100% sure that the CPU is good, but all of the pins are good and the fan still works great.

I am guessing that the BIOS may have a list of CPUs that it will accept?

It is a Phoenix BIOS, and I am comfortable with a hex editor, but I am not sure where to start..

Thoughts?

Reply 1 of 6, by Deksor

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I'm not sure if I can help you much, but I'd advise you to dump the bios and upload it somewhere.

Furthermore, would you like to help us document your computer on UR ? We have a page here https://www.ultimateretro.net/motherboards/2835

We'd need the BIOS and a nice photo of the motherboard (I have a similar hp Vectra and to release the motherboard you need to unscrew a metal thingy on the side and the slide the motherboard out)

To dump the bios, use this http://cd.textfiles.com/microhaus/mhblackbox3 … MORY/GETROM.ZIP

Edit : according to the hp service manual found on this page https://www.ultimateretro.net/motherboards/6691 (it's a general one for all hp computers from the time ), there are three bios versions. The latest one frop 1993 (T.04.04) was apparently available on HP's bbs. Maybe this would solve your problem and maybe it's floating around online ?

Last edited by Deksor on 2022-03-13, 21:54. Edited 2 times in total.

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Reply 2 of 6, by bc732

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Crap, yes, I feel dumb now. I actually was able to find V.04.09, and it is booting now. Though, it is only recognizing it as 63mhz, no matter what I set the bus speed to. Will have to play with that.

Thank you, and yes I will try to get photos of the motherboard when I get a chance.

Reply 3 of 6, by TheMobRules

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Getting a POD to work on a pre 1995 motherboard is kind of a lottery, since apparently Intel altered the original specifications for the Pentium Overdrive shortly before release. So with that CPU it's not like the other 486 Overdrives which work just fine with the settings for a 486DX, the POD usually has specific jumper combinations to work properly.

An updated BIOS might help, but I don't know if that will be enough.

Reply 5 of 6, by bc732

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Ah nevermind, it seems to just be what the BIOS is reporting. With 33mhz bus, a software diag sees it at 83mhz. Or with 40 it shows 100mhz, so I am wondering if that is stable

Edit: No, it is not stable at 100mhz. 83 is great. Cheers all.

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