appiah4 wrote on 2022-03-09, 08:35:

I got these in a batch I recently bought. Apparently I already had one stick of these in my stash, now I have three. The probl […]
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I got these in a batch I recently bought. Apparently I already had one stick of these in my stash, now I have three. The problem is, I can't figure out what it is. It has 12 ram chips (6 on each side) marked:

ACTCTS
9806Y EDO
TM5117205BJ-6

I can't seem to find a datasheet for the parts and the x12 configuration is extra strange. Googling only got me to a few places selling them as PS/2 memory, 32MB for the dual sided stick.

Can anyone shed some light on what these may be?

Its possible they are custom/proprietary Simms which may make finding any data on them difficult.

Do you have some macro shots of the Simms showing the writing on the PCB ? both sides . .if there is anything marked on the other side.

No better shots I'm afraid, the photos show each side of the pair.

appiah4 wrote on 2022-03-09, 09:08:

No better shots I'm afraid, the photos show each side of the pair.

I found the same simms for sale from Electromyne that had some details but likely no more than you already know

I think it's so they can get away with RAM chips that might have faults. Those shorting pads 1-6 go between the SIMM data pins and the RAM chips. On the chip, it looks like DQ1 goes to Pad 1, DQ2 goes to pads 2&3, DQ3 goes to pads 4&5 and DQ4 goes to pad 6. Then the 6 pads go to just 3 of the SIMM edge connector, pads 1&2, 3&4, 5&6 are connected in pairs. Then by putting solder blobs on the pads as appropriate they can select which 3 bits (out of 4) are actually used.

I think it's wired like this:

1Chip    Pad     SIMM Edge
2
3DQ1-----1 1-\
4             >-- D
5     /--2 2-/
6DQ2-<
7     \--3 3-\
8             >-- D
9     /--4 4-/
10DQ3-<
11     \--5 5-\
12             >-- D
13DQ4-----6 6-/

[edit: the ones with only 2 blobs are similar, but only have 2 connections out the SIMM edge. So DQ1,2 or 3 can connect to one (via pads 1,2 and 4) and DQ2,3 or 4 can connect to the other (via pads 3,5&6). In the photo it looks like these have blobs on 1&6, so using DQ1 and DQ4]

In this case, the common solder blob connections are pads 1,3,6. Those will connect DQ1, DQ2 and DQ4, leaving DQ3 unused. 4 of the chips only have 1&6 shorted, so only used DQ1 and DQ4. That means each group of 3 chips provides 8 bits (3+3+2). In total that's 32 bit, so they're probably non-parity EDO. Presence detect pads D1-4 are all open, don't know if that says anything about the size and speed. No idea what the E or F pads are for.

Looks like there are more pads to connect lines A10 and A11 (maybe V=+ve, G=Gnd, S=switched?). A10 is connected to S and A11 is not connected. So maybe that means A0-10 are used, which I think means maximum 4M x 4bit chips, with 4MB per group of 3, so 16MB total. Could be less.