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Olivetti Modulo M4 40 with DX2 wont start

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First post, by SVD

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Hi,

I am trying to fix and upgrade a Olivetti Modulo M4 40. It comes with a 25mhz 486 SX onboard. It starts fine with the SX, but when i install a DX2 in the other CPU slot it does not start, well the PSU does and the power led is on, but no beeps or anything.

I have tried a regular Intel DX2, a AMD DX2 and a Intel overdrive DX2. Same result.

I have set the jumpers according to the manual, and tried all other combinations of the CPU selection (not that there is many). Also the 25/33mhz jumper

This is the board: https://stason.org/TULARC/pc/motherboards/O/O … 4XX-BA204X.html

Is the socket broken or something?

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Reply 1 of 5, by ppsh41

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Check the board type. If you have the T.1 (assy: BA2034 as I suppose, standard for M4-40 model) the PGA socket is an Overdrive socket. In this case, you can only put an Overdrive processor with the extra pin (169 pin, ODP-type), to disable the soldered CPU. For example, the DX2ODP66. The more common DX2ODPR66 doesn't work.

As a a reference:
https://www.cpu-world.com/CPUs/80486u/index.html

In this post you can find the service manual for M4-40/PCS-44C, if you need it:
Olivetti M4-40/PCS-44C/Familia2 setup disk

Reply 2 of 5, by pentiumspeed

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Need to short one pin on the CPU socket (solder a low value resistor) that disable the soldered 486SX.

Here's the thread detailing this.

487SX 169pin socket: any way to use a normal 486DX2 there?

Cheers,

Great Northern aka Canada.

Reply 4 of 5, by SVD

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It's alive 😁😁 Feels great to make something work with a hack like this.

I used a 550ohm resistor at first, it was enough to start with the beeps but it would not start ram check. So it is on the high side maybe. I went with a 39 ohm and everything is fine. Would be more elegant with the resistor at the ground end tho 😅

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