• Please review our updated Terms and Rules here

Presentation and help for an XT Expansion Card (Warning, for EE Enclined)

A

AnalogThinker

New Member
Joined
Feb 9, 2023
Messages
9
Hi everyone,

[Presentation]
I am located in Canada, and have been fixing Computers for a while now (mostly on the Hardware level).
My journey with the IBM started when a friend dropped a VERY early revision of a 5150 (SN before 3000)
1675980650283.png
1675980726325.png

I spent a good 2 weeks probing thousands of traces to figure out the issues:
Symptoms: Upon turn on, I sometimes had nothing, sometimes a continuous beep that triggered when environment capacitance changed (hovering my hand for ex).
Faults: It's been a while but from what I remember, it was a combination of: Bad 8255A-5 that had one of the outpus stuck in floating (Z) state, a bad track reaching U67, a seriously drifted Crystal, as well as a flaky ROM.

[Current situation]
Now I just have acquired a large lot of IBM machines, and now focusing on the 5150 and 5160 that I am trying to restore slowly.
1675977025655.png

One of them had a Diamond Flower MF-100 that I need some help with!
1675977172636.png

Can you spot the issue?

After a couple of hours probing, I realized the Data In of the 4164 was floating with no activity, so I traced it to all the chips and to my surprise, all the pins of the Logic it was attached to were Input pins, no-one was sending Data.
That's where I tried to find pictures and realized it was a Diamond Flower MF-100 and U68 should be a 74280 (but it had a 7432 from factory?!). No wonder it didn't receive anything!
I found the only one I had in my stash and replaced it. But now, we're continuing the troubleshooting.
(BTW I have tested every single chip of that board, RAM and Logic).
It turns out my issue is the U60 (DM74S573N), a Schottky TTL-PROM. It gets the proper inputs from the Jumpers and the Address lines coming from the ISA bus, but it's a dud and all outputs are floating.

[Tricky part]
- All the Datasheet for the DM74S573N out there are for the newer 20pin, except for one screenshot from EEVBlog's forum:
1675978643266.png
- There is no data on how to "Program" it anywhere, and Datasheet mentions it comes blank.
- I do not have enough understanding on how the additional memory are addressed on Add-On Memory Cards to rebuild a Frankenstein drop-in replacement module.
- I do not have the original 4096 bits table

[Ask for the group]
Is there ANYONE out there that has the same card (I believe it would be compatible with the "Jameco JE-1078", and the "Donatec Ram Exp.") and would be up for a challenge of extracting the ROM and map the 4096 logic table (with an Arduino Routine for example, that I could help build of course)?
And does anyone has any clue how to PROGRAM that ROM. If not, I'll have to find or design an alternate Frankeinstein drop-in solution from a PAL, ROM, or STM32/AVR maybe.
(Or a non-working one for sale, but where's the challenge...)

Anyways, thanks for your Time and Interest!
 
You can start with finding out to what the inputs and outputs are connected. If it only takes care of the I/O part it should be relatively easy to compose your own table. If you use a GAL16V8 as equivalent, you can plug it in the original socket. Yes, it is 20 pins but connect pin 1 and 20 to pin 19 using a wire. When using this GAL or equivalent you can use (win)CUPL to create the needed JED. To program the GAL you'll need a programmer. The TL866II is a good one.
FYI: I used this trick to replace the PAL on the boeard of a PC clone so I could insert 3 banks of 256 KB DRAMs to have the extra 128 KB as UMB.
 
Huh... The "newer" 74S573 spreadsheet show garbage for the 20-pin DIP part. For example, it shows 8-bit data output (it is 4-bit in the description). So I think when editing the spreadsheet, the picture was copied from 74S473 spreadsheet.
Also... it is weird that 74*573 part number was later reused for 8-bit D latch (e.g. 74F573, 74LS573)... which is a 20-pin part
 
I was wondering about that to. But I have the 1991 version of the data book for the normal, S and LS version but it doesn't mention none of these for the 573. And I never saw one of these either. I don't have a book about the Advanced version, AS and ALS, but I know that at least the ALS version exists because I use them quite often.
 
Ruud said:
You can start with finding out to what the inputs and outputs are connected. If it only takes care of the I/O part it should be relatively easy to compose your own table. If you use a GAL16V8 as equivalent, you can plug it in the original socket. Yes, it is 20 pins but connect pin 1 and 20 to pin 19 using a wire. When using this GAL or equivalent you can use (win)CUPL to create the needed JED. To program the GAL you'll need a programmer. The TL866II is a good one.
FYI: I used this trick to replace the PAL on the boeard of a PC clone so I could insert 3 banks of 256 KB DRAMs to have the extra 128 KB as UMB.
Click to expand...
Excellent thanks! Good starting path, I didn't realize the TL866 could program those, that's good to know. I probably have a bunch of GALs around. Without the original table available, I'll have to dive into how the expansion RAM cards are addressed and try to work on something, guessing there will be a lot of trial and error and computer freeze haha! I believe the switches operate like any other RAM card, Start RAM address and Size.
 
I just checked if those PROMs are supported by the TL866 or Retro Chip Tester (RCT). Sadly, I could not find these in the TL866 list. The RCT might be able to read them. However, this seems to be untested (link). I will familiarize myself with this function of the RCT when I have time. So far I have only used it to test DRAMs and haven't even updated the firmware since I bought it.
Are there any other options to read those PROMs?
 
Take an old EPROM, gut it, piggyback a 18-pin socket on top of it and connect all pins with the address and data lines of the gutted EPROM. Insert the PROM and read it as a 27xx.
 
Kanpai said:
I just checked if those PROMs are supported by the TL866 or Retro Chip Tester (RCT). Sadly, I could not find these in the TL866 list. The RCT might be able to read them. However, this seems to be untested (link). I will familiarize myself with this function of the RCT when I have time. So far I have only used it to test DRAMs and haven't even updated the firmware since I bought it.
Are there any other options to read those PROMs?
Click to expand...
Worst comes to worst, I was thinking about developing a quick and dirty program for the Arduino platform that would send all the address options sequentially and read the outputs. Ideally would just need a proto board and a few wires.
 
Ruud said:
Take an old EPROM, gut it, piggyback a 18-pin socket on top of it and connect all pins with the address and data lines of the gutted EPROM. Insert the PROM and read it as a 27xx.
Click to expand...
Thought about it, do you think an EPROM would have the ability to have the Z-State, and also meet the "Schottky" speed critera from the PROM? Even if, I'll still need to find the original logic table before I can try it.
 
I am an EE but sorry can't provide much help to your question. I just wanted to say that's a LOT of IBM computers. I'm sure there's at least one person seeing this whose is a little envious.
 
AnalogThinker said:
Worst comes to worst, I was thinking about developing a quick and dirty program for the Arduino platform that would send all the address options sequentially and read the outputs. Ideally would just need a proto board and a few wires.
Click to expand...
That is maybe better than my idea. Not all people are familiar with an Arduino, that's why I suggested the converter.
 
AnalogThinker said:
Thought about it, do you think an EPROM would have the ability to have the Z-State, and also meet the "Schottky" speed critera from the PROM? Even if, I'll still need to find the original logic table before I can try it.
Click to expand...
You mean using an EPROM for replacing the PROM? Sometimes it works, an example: an EPROM replacing the PLA of a Commodore 64, but in this case: the EPROM is much bigger than the original PROM. Using a GAL is safer.
 
I have read the IC with the RCT pro and was able to save "something" from it as a bin-file. I hope this will be helpfull in any way.
 

Attachments

  • N82S137N - MF-100.zip
    255 bytes · Views: 2
You must log in or register to reply here.
Back
Top