27 Sep
2021
27 Sep
'21
10:52 a.m.
On 2021-Sep-27, at 8:23 AM, Tom Hunter via cctalk wrote:
While restoring and repairing a Data General Nova 2/10
I found a bad
bipolar PROM on the CPU board. The PROM has open-collector outputs and is
organized as 32 words by 8 bits. It appears that one of the open-collector
driver transistors is faulty (but it could also be that a fuse has
"healed").
The part is an Intersil IM5600CP, but these were also made by others, for
example Signetics and Philips made the 82S23 and TI and NTE made the faster
SN74S188N. Some vendors still sell these parts and there are even a few on
Ebay.
How do I program these PROMs? I found one somewhat obscure description of
the algorithm in the NTE datasheet, but I suspect that each manufacturer
had (somewhat) different algorithms.
Is there an affordable commercial programmer out there which can program
these PROMs?
Is there a simple design out there which I could breadboard for a one-off
programming job (maybe using an Arduino to control the programming
sequence)?
The hardware & software for a one-off breadboarded programmer is, or should be, easy
enough with a ~ few-hours/1-day effort if you wanted to go that route.
I did this 8 years ago for a PROM in a HP9830 - a 256*4 Intel 3601 PROM, for which I
burned, and replaced with, a TI 74S387.
(In the end in turned out it was an unnecessary effort, one data-line from the PROM was
showing bad but the failure wasn't the PROM output, it was the input of the IC the
PROM was driving.)
Programmer hardware was 3 TTL ICs, 2 zeners, 6 transistors (more specifically
2+numDataLines) and a few resistors on a solderless breadboard, and a bench power supply
for the programming voltage. Software was a python program running on a RPi. All
program-pulse timing was done in user-land on the RPi.
I can send along the schematic and program if you wish, there will be some adaptation
required of course. Details of the 74S188 programming/burn algorithm is in the 1975 TI
Memory Databook for Design Engineers (available at bitsavers) (I expect the 188 is the
most likely type you'll find NOS today).