Can an ordinary 486 CPU be used with the Overdrive socket? \ VOGONS

Can an ordinary 486 CPU be used with the Overdrive socket?

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First post, by perhenden

Posted on 2020-04-12, 21:32

perhenden Offline

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My 486 motherboard has a non-removable 486 sx-25 chip, and an empty overdrive socket (socket 1).
The best choice would be to get hold of an overdrive CPU, and insert it into the empty, waiting socket.
To save money I would like to use a 486 DX2-66 CPU available to me for the upgrade. The motherboard supports this speed.
Can I put the 168-pin 486 dx2 in the 169-pin overdrive socket? Will it fit, will it work? (doesn't have it yet, cannot test).

Option 2: Is it risky to de-solder the sx-chip and insert the dx2 chip in its place?

EDIT: This is a Compaq Presario 425 mother board.

Last edited by perhenden on 2020-04-13, 09:14. Edited 1 time in total.

Reply 1 of 4, by Horun

Posted on 2020-04-12, 21:59

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What is the manufacture and model of your motherboard ? I had a soldered SX-16 with a OD socket that allowed a DX33 as well as an ODP, just had to change a few jumpers.
How would you insert the DX2 PGA where the SX-25 SMT is ? You would have to solder in another socket, which you already have one...so NO !

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 4, by mpe

Posted on 2020-04-12, 22:34

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It depends.

If you can't remove the original CPU, it needs to be disabled somehow. As designed by Intel this is normally done by UP# pin which is an input signal on standard processors and output on the overdrive (ODP models). Thus when inserting the Overdrive chip to the socket he original CPU sees the signal from the upgrade chip and disables itself.

But as mentioned above some motherboards have jumpers that can do it without assistance from the Overdrive chip. You can also modify the socket (or the CPU). All you need to do is to set UP# signal to low which might be easier than unsoldering the chip.

If you disable the original chip somehow then you can use any chip in the overdrive socket. It doesn't have to be overdrive model.

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Reply 3 of 4, by perhenden

Posted on 2020-04-13, 09:15

perhenden Offline

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Horun wrote on 2020-04-12, 21:59:

What is the manufacture and model of your motherboard

This is a Compaq Presario 425 mother board.

mpe wrote on 2020-04-12, 22:34:

If you disable the original chip somehow then you can use any chip in the overdrive socket. It doesn't have to be overdrive model.

Nice! There are jumpers to disable the on-board CPU, for when using the overdrive socket.

Thanks, this makes me happy 😀