Here is the some positive update for this project 😀

Finally I was able to run it with the 4 SIMM modules, both Toshiba and Siemens works well. But... It can not run both DIP and SIMM at the same time, it is a pity, I'm afraid that it unable to support more than 4 meg at once. So sad, this MB shows optimal performance for 386-33 cpu, see results attached.

I have played a bit with SW 2 and found:
Switch 5 from SW2 do the selection of memory type
So here is the SW2 config for SIMM
1 1 1 1 1 1 0 0 boot as 640K
1 1 1 0 1 1 0 0 boot as 1664K
1 1 0 1 1 1 0 0 boot as 2688K
1 1 0 0 1 1 0 0 boot as 3712K

I have tried to trace the SIMM pins, and found that most address lines except A10 and A11 goes to U95 and U94 IC chips marked as "74F244PC" (A0-U95_18, A1-U95_16, A2-U95_14, A3-U95_12, A4-U95_09, A5-U95_07, A6-U95_05, A7-U95_03, A8-U94_14, A9-U94_12). Address lines from DIP connected to U93 and U94, was able to trace 10 lines. Not finished with the expansion memory slot, just found that Data lines from SIMM may be found within the slot pins.

As for the jumpers, did not dig deep, but it looks like jumper W6 has connected to 16MHz oscillator, W5 connected to IC U68 marked as "DM74LS175N"

Will continue with tracing and post updates.

Susanin79 wrote on 2022-07-11, 22:59:

I have tried to trace the SIMM pins, and found that most address lines except A10 and A11 goes to U95 and U94 IC chips marked as "74F244PC" (A0-U95_18, A1-U95_16, A2-U95_14, A3-U95_12, A4-U95_09, A5-U95_07, A6-U95_05, A7-U95_03, A8-U94_14, A9-U94_12). Address lines from DIP connected to U93 and U94, was able to trace 10 lines. Not finished with the expansion memory slot, just found that Data lines from SIMM may be found within the slot pins.

This makes sense. 10 bits for row and 10 bits for column and four 30-pin simms means the board handles 1 mega-dword or 4 MB of RAM onboard.
Maybe that extra ISA-like slot near the memory was for an expansion card and only via the proprietary expansion card could it handle more than 4MB (and could also explain more switch settings).

Wow that is great you got the SIMMS to work, to bad cannot get both to work yet.
From what I see in your SW2 switch settings: Sw2-5 seems to be what changes reading the DIPs to SIMMS
"X X X X 1 X X X did not boot" "with installed DIP modules" (from earlier) and comparing to your new switch detections with SIMMS, when closed it reads the SIMMS. Open reads DIPs.
Does that sound correct ?
Maybe if the DIPS were 256kx1 it might be able to read 5MB (with SIMMS) but maybe not. I see no U# marking around the DIP sockets (making them unique as the SIMMS sockets do have them)
so maybe it can only read up to 4MB on board as jake says 🙁

I have such a board, experimented with it a few years ago, was able to figure it out and launched simm and dip collaboration, got a maximum of 8 megabytes. The secret is in the unusual memory of simm modules ) I searched and picked up the debt. And the coprocessor worked iit387 .