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MK4128 DRAM

S

Sabertooth

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Joined
Apr 20, 2019
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36
Location
Texas USA
Curious, does anyone have the pinout of the MK4128 DRAM chip. This is not the piggybacked 4128 on the type 1 IBM motherboard. These are single 4128 chips on an old video card and I can't find anything on these anywhere.

I didn't think they ever made a single 4128 but they evidently do because they are on a monochrome video card that I would like to check.
 
Are you sure that's not a MK41128? I believe that Mostek did the same thing that Intel did around 1983--took half-good 256K DRAMs and relabeled them as 128K--i.e. MK41256. During the DRAM shortage, people would buy anything.
I think I still have a batch of Intel 2109 DRAMs (half of a 16K one).
 
I guess it could be. I just know it is actually stamped MK4128N-xx. I'm at work and the xx of course is the speed that I can't remember off the top of my head. It is interesting.
 
The 'standard' (for want of a better word) MK4128 is of a 2-chip piggybacked arrangement, two 64K-bit chips.
Pictured at [here].
The top chip is slightly different to the bottom chip; RAS is pin 3 on one chip, pin 4 on the other chip.

In the 'same vein' as what Chuck suggested, perhaps (repeat: perhaps) Mostek:

1. Produced batches of the RAS-variant-1 64K-bit chip (the 'top' chip), stamping them as MK4128 at the time (easier to do then, rather than later in the piggybacked arrangement); then
2. Tested those chips, discarding failures; then
3. Produced batches of the RAS-variant-2 64K-bit chip (the 'bottom' chip), leaving them unstamped; then
4. Tested those chips, discarding failures; then
5. Piggybacked the good chips (RAS-variant-1 on top of RAS-variant-2); then
6. Tested the piggybacked combination as 128K-bit (in case of bad soldering, etc.)

Of the discards of step #2, ones that failed only in the second half were sold to OEM's as 32K-bit chips, but unfortunately sold still labelled as 'MK4128'.
Mostek will have had to inform the OEM of which pin (3 or 4) was the RAS pin.
 
It will not Initialize so I don't know but since it's it vintage, I want to repair it and I thought I'd put it in a memory tester. Without knowing the setup, I'm not sure how to set the tester. My tester can check 4128 piggyback memory but I doubt it will check these. I can reprogram the tester if I knew the pinout.
 
A related chip is the 18-pin MK4528
Two 64Kb chips on the same carrier. I suspect the MK4128 was an earlier design that employed 2 64Kb chips.

The MK4128 would be two 64Kb chips specially configured. Note that there are two RAS inputs (RAS0 and RAS1), so each chip can be individually accessed. The MK4528 adds a couple of pins (DIP18) and separates the CAS lines as well (RAS1,RAS2/CAS1,CAS2) but the idea is the same.

So, I suspect that the chips on your video board are 64Kb and are half of a MK4128. See if your board reports the memory accordingly.

Also, check the pinout. It would be unusual for a video board to use MK4128s--trace the lines and see if they agree more with a 4164.
 
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