• Please review our updated Terms and Rules here

IBM Enhanced Memory Expansion Adapter not working

mikeyp

mikeyp

Experienced Member
Joined
Apr 16, 2019
Messages
84
Location
Leicestershire, UK
Can anyone offer any insight into my latest problem please?

I have an IBM AT which currently has an AST Advantage expanding it to 640kB. This works fine and POST counts to 640kB. I wish to remove it and add the below:

I have bought the board pictured below. It's marked ASM 55X3543 EC A25158.
RAM is 2x 1Mx9 Kingston modules. Both tested and passed in a Retro Chip Tester Pro for memory and parity errors.
It won’t register on the system. Post stops at 512kB and reports a memory error. Base memory should still surely be 640kB though as that remains configured in the BIOS?

DIP Switches are configured per the manual for 512kB system base memory and a 1MB starting address for expansion memory.

1: On
2: On
3: On
4: Off
5: On
6: Off
7: On
8: On - LPT/COM Enabled - Untested at this point.

Any thoughts/advice appreciated please. I'd really rather not have to send it back to the seller in America.

IMG_4501.jpeg
IMG_4502.jpeg
 
mikeyp said:
It's marked ASM 55X3543 EC A25158.
Click to expand...
The 55X3543 does identify the card as an 'IBM Enhanced Memory Expansion Adapter'.

( Per page 1-4 of the Guide to Operations manual. )

mikeyp said:
DIP Switches are configured per the manual for 512kB system base memory and a 1MB starting address for expansion memory.
Click to expand...
Looking at the manual, that is how I would be setting the switches for your configuration.
I see that in the photo that you provided, the switches are set that way, and they are also set that way in the photo at [here].

mikeyp said:
It won’t register on the system. Post stops at 512kB and reports a memory error. Base memory should still surely be 640kB though as that remains configured in the BIOS?
Click to expand...
Yes, with the CMOS SETUP set for 640K of base memory, and your card configured to provide RAM in the 512-640K address space, the POST is expected to be counting past the 512 KB point.

You have the SIMM's in the two top sockets, which is what is indicated in the Guide to Operations manual.

mikeyp said:
Any thoughts/advice appreciated please. I'd really rather not have to send it back to the seller in America.
Click to expand...
There may be a dirty, or not-fully-home, switch. If you have not already, try rocking the switches back and fourth a few times.

A question is, do industry standard SIMM's work on this card, or are IBM types required. Page 3-5 of the Guide to Operations manual shows IBM part numbers (as expected), but those could be industry standard or IBM type. The answer may be in a previous thread about the subject card.
 
modem7 said:
A question is, do industry standard SIMM's work on this card, or are IBM types required. Page 3-5 of the Guide to Operations manual shows IBM part numbers (as expected), but those could be industry standard or IBM type. The answer may be in a previous thread about the subject card.
Click to expand...

Damnit. I think you're right. I thought this machine was too early for this tomfoolery of theirs. Looks like my soldering iron is warming up tomorrow then!

I looked up a few of the part numbers, settled on 68X5721 - the 1MB SIMM and then came across this:

from here https://ardent-tool.com/IBM_SCSI/SCSI-C.html

2MB SCSI w/cache

Increasing the cache to 2MB

One module that can be used to expand the IBM SCSI Adapter with cache /A from 512K cache to 2MB cache is the IBM P/N 30F5360 / FRU 74X8637, which is a 1MB x 9 bit (Parity) 100 ns module *with* IBM-specific presence detection. These IBM modules are in the Mod. 30-286 (8530-Hxx or -Bxx) with 80286 CPU - if anywhere at all.

MY 1MB SIMMs are marked MSC2314-12YS9A 183004 68X5721.
It has 9 OKI M511000A-1AJ chips, mnf. 89335521
Kingston modules labeled KTM-1000/M30 (From Peter)

From Jerry Dumer:
I have 3 boards with Toshiba THM91010AS-10 SIMMs that do the job fine. I found these on a memory card in a Model 60. They are gold pins. I imagine Toshiba made them for the 30-286s. They do work.

Trying Non-Compatible SIMMs

If you try some likely looking 30 pin SIMMs and they don't have the correct CAS/RAS wiring, the system will disable them it and you will see SCSI Adapter w/Cache with 0KB. Don't freak out. Replace the original SIMMs and run Advanced Diags and test the SCSI Adapter to restore your 512K cache. Been there, done that.

Converting Industry Standard Memory

Yes. Alfred Arnold has finally figured it out. Dr. Jim Shorney confirms this triumph. The biggest hurdle was the IBM modules have a different RAS/CAS scheme in addition to the different pin-out. As time goes on, exceptions MAY be found. News as it happens.

Alfred's 30-pin SIMM Hack (original HERE)

For those that have the burden of college education, I made some assumptions. First, the SIMM pins will always be performing the same function (like parity Data Out, parity CAS). Second, those SIMM pins can be used to positively identify the parity chip's DO and CAS pins.
This makes manufacturer's data sheets unnecessary. Assuming they even have them.

  1. Break connection between SIMM pin 26 and parity chip's DataOut pin; This inferrs that SIMM pin 26 goes to Data Out-
  2. Connect parity chip's DataOut pin to SIMM pin 29
  3. Tie parity chip's lead that USED to go to SIMM pin 26 to SIMM pin 29
  4. Break connection between SIMM pin 28 and the parity chip's CAS pin
  5. Parity chip CAS is attached to SIMM pin 28
  6. Connect parity chip's CAS pin to SIMM pin 2
  7. Attach lead that used to go to SIMM pin 28 to SIMM pin pin 2
  8. Connect both SIMM pins 26 and 24 to SIMM pin 22 (GND).
  9. Tie SIMM 26 and 24 off to SIMM 22
{/QUOTE]
Click to expand...
 
Getting somewhere. I performed the surgery on the modules and the error code has changed. It switches if I switch the modules around so either I have damaged one or have a bad solder joint.

I cut the trace above pad 26, scraped back the solder mask and joined the trace to pad 29.
IMG_4521.jpeg

I cut the trace above pad 28 and joined the trace so it would meet pad 2. I then joined pads 24 and 26 to ground on 22.IMG_4520.jpeg

The error is no longer FFFE but C000 or 00C0 depending on the simm pair orientation.

IMG_4519.jpeg
IMG_4518.jpeg

This does at least tell me the card is doing something, these should be working modules and I can decide what to do next regarding getting working RAM.

Should I:
1) Obtain and modify more SIMMs in the hope this will work?
2) Design and create some. Might need some help with this. Not something I have enough experience with but would help anyone else in the community who needs these SIMMs.
3) Anyone got any official IBM ones they’re willing to sell to me?
 
Thank you. I have ordered more ram per option 1. I will wait and see what arrives and report back in a couple of weeks.
 
I've had an extremely hard time sourcing SIMMs that actually work with the IBM EMEA. So far, the only ones that I can get to work in it are the ones that happened to be on the board when it got shipped to me from Ebay. I have no idea why this is the case, perhaps its some kind of a timing issue?
 
djfitzgerald said:
I've had an extremely hard time sourcing SIMMs that actually work with the IBM EMEA. So far, the only ones that I can get to work in it are the ones that happened to be on the board when it got shipped to me from Ebay. I have no idea why this is the case, perhaps its some kind of a timing issue?
Click to expand...
It's not a timing thing. It's definitely that they're the IBM proprietary format as used in their PS/2 SCSI adapter with their horrible IBM presence detection. I modded a couple of industry standard sticks as above and they at least register. Sadly I damaged one in the process so am waiting on more to arrive to butcher.
 
@mikeyp what would you recommend as a good stand-in to sacrifice to do the mod? I bought a whole bunch of 30 pin IBM simms thinking they would work and they did not...
 
lyonadmiral said:
@mikeyp what would you recommend as a good stand-in to sacrifice to do the mod? I bought a whole bunch of 30 pin IBM simms thinking they would work and they did not...
Click to expand...
Standard 30 pin 1M x 9 SIMMs. I've just recieved the batch I was waiting for. They took AGES to ship. I just need time to mod them now.

Meanwhile, something interesting has happened. I sent the modules I modded to Germany and the IBM 1M x 9 Parity test and 256K x 9 Parity test are going to be included in the retro chip tester pro firmware.
https://www.reddit.com/r/RetroChipTester/comments/16yrkat

How would you feel about posting me a pair of your IBM modules to test, confirm they are indeed IBM ones and see if they work in my EMEA card? Stephan (Retro Chip Tester Pro creator) would like if we could confirm the tests with genuine modules also but I don't have and can't source any.
 
You must log in or register to reply here.
Back
Top