exxos's Atari, Amiga & retro forum

Hi from south of France and sorry for my average english.

I would uprade RAM on a 1040 STE with 4x1Mo simm Samsung KMM591000B-7, featuring 9xKM41C1000BJ-7 chips (20pin).
I need some advices to see if and how I can remove the parity chip.

The simm datasheet is available on pdf on website datasheets360.com
Simm pin 26 = PQ Data for parity, is connected to chip #9 pin 19
Simm pin 28 = PCAS CAS for parity is connected chip #9 pin 18
Simm pin 29 = PD Data for parity is connected chip #9 pin 1
So i guess chip 9 is the parity chip

Testing other pin continuity on the chip #9 gives:
pin1 = PD Data for parity (to simm pin 29)
pin 2 = W read write input (to simm pin 21)
pin 3 = RAS Raw Adress Strobe (to simm pin 27)
pin 4 = ? (to all chips pin 4)
pin 5 = seems not connected
pin 6 = ? (to all chips pin 6)
pin 7 = A1 adress input (to simm pin 5)
pin 8 = A2 adress input (to simm pin 7)
pin 9 = A3 adress input (to simm pin 8)
pin 10 = VCC (to all chips pin10 + simm pin 1 & 30)
pin 11 = A4 adress input (to simm pin 11)
pin 12 = A5 adress input (to simm pin 12)
pin 13 = A6 adress input (to simm pin 14)
pin 14 = ? (to chip 8 pin 14)
pin 15 = A8 adress input (to simm pin 17)
pin 16 = A9 adress input (to simm pin 18)
pin 17 = seems not connected
pin 18 = PCAS CAS for parity (to simm pin 28)
pin 19 = PQ Data for parity (to simm pin 26)
pin 20 = VSS ground (to all chips pin20 + simm pin 22)

My knowledge stops here

Questions:
- Does chip#9 is the parity chip indeed ?
- Can i remove it on this kind of simm ?
- If yes, after desolering the chip do I'll need to make some jumper connections on the simm pcb ?
- If yes what tests can I do before setting the simm safely in the atari ?

Many thanks

Fred

Sbn31 wrote: 20 Jan 2026 13:35 Hi from south of France and sorry for my average english.

I would uprade RAM on a 1040 STE with 4x1Mo simm Samsung KMM591000B-7, featuring 9xKM41C1000BJ-7 chips (20pin).
I need some advices to see if and how I can remove the parity chip.......

Questions:
- Does chip#9 is the parity chip indeed ?
- Can i remove it on this kind of simm ?
- If yes, after desolering the chip do I'll need to make some jumper connections on the simm pcb ?
- If yes what tests can I do before setting the simm safely in the atari ?

Many thanks

Fred

:wecomewave:

And don't worry your English is fine, certainly better than my French :)

So first point would be honestly, it's just 4 SIMMs and you can probably find non-parity 30 pin modules cheaply on ebay rather than going to all the Palaver of modifying the ones you have and possibly damaging them in the process.

To answer your other questions, in the first case since you have 9 ICs, then the datasheet should tell you what IC is the parity chip. If it doesn't then you may be relegated to guesswork even though you've gone through the configuration.

If you can ID the chip and desolder it, then it likely will work, but you may need to solder some pads, and again, if the datasheet is decent, there should be some information about pads and how they are used.

If the datasheet you have isn't really helping I'd suggest looking for another, I've often found variations which are better then my originals.

Have you tried the simm as they are?

Hi many thanks for your answers, of course I could buy new ones but if it is just as simple ad remvoving the last chip (like on attached pictures) , I can just do it.
Yes I've tested the ram but the ste is a bit instable in all config (2M or 4M).

PSU recap is first point of all for unstable machines. The simm / parity issues tend to only be a problem with the 1712 shifter.
It would probably help if you post a image of your motherboard.

Hi, psu have been recaped + new bridge rectifier 2 month ago. Here is a pic of the motherboard, the shifter seems to be a 1712 indeed.

Sbn31 wrote: 26 Jan 2026 16:38 Hi, psu have been recaped + new bridge rectifier 2 month ago. Here is a pic of the motherboard, the shifter seems to be a 1712 indeed.

Yeah, you probably should remove the parity chip then..

Hi, finally I've managed to remove parity chip from these simm, RAM test is ok, that's working fine. Many thanks for your help !