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Where to start with this home made system?

cluttered

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Jul 20, 2013
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Adelaide, Australia
Some time ago I was gifted a S100 system by a generous (former) co-worker. But when I agreed to take it sight-unseen, I didn’t realise how much of a “project” it is!

It looks to largely be home made; the “console” appears to be scratch-built, and it has a built-in 8-inch drive along with an external 5 1/4 drive, plus the S100 chassis itself of course. The processor (Z80) card is wire-wrapped. I have no media or documentation for the system.

I haven’t yet tried to power it up, that seems unwise in its current state. But I suspect that I might be in over my head with this; I’m a software guy, not a hardware guy. I’ve repaired simple TTL stuff before but that’s about my limit.

So I’m after advice for how I should best proceed. My guess is to start by carefully checking each board for obvious shorts, and to work out how it should connect together. Looks like there’s a RS232 output on the back of the chassis, which is intended for connection to the console. There's various spare cables and cards too.

It’s a fascinating bit of kit, someone must have spent many hours building this. The person I got it from bought it from the original owner a long time ago and used it for a while before putting it in storage for a long time.

Thanks!

s1.jpgs2.jpgs3.jpgs4.jpgs5.jpgs6.jpgs7.jpgs8.jpgs9.jpg
 

krebizfan

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Some of the other cards look to have etched boards and thus might have documentation when recognized. Maybe take a picture of each board as you examine it and post it here. Perhaps someone (probably not me) will know what the board is.
 

wperko

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Jul 4, 2007
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146
Hi,

Before taking any more photos, you should cover up the glass on all the PROMs that don't have labels over them. Light erases PROMs.

Good high-resolution photos of each board front and back helps to identify the boards and the revisions of the boards.

Kind'a looks like a Cromemco home-built.
 

JonB

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That's a heck of a thing. Look for ROMs and dump them with a reader. There may be a monitor or other bootstrap.

Gosh imagine getting CP/M running on it, assuming it's not a clone of something (like a Cromemco, as suggested). What a challenge!
 

cluttered

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Messages
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Location
Adelaide, Australia
Thanks for the replies and suggestions.

I had a look at each card in the chassis (and took a photo of each, won't bother posting them unless needed). As far as I can tell there is:
  • A floppy disc controller card (judging by the FD1795B-02 in the middle of it plus the two ribbon cable connectors)
  • A bus extender card (labelled "S-100 EXT CARD LOGIC PROBE")
  • The CPU card (Z80 based, wire-wrapped construction, I'd hate to try to fault find that!)
  • A serial/parallel I/O board (one of these: http://s100computers.com/Hardware Folder/Jade/1P2S/1P2S.htm)
  • A 64K RAM board, not fully populated
  • A 16K RAM board, fully populated
As well as the above cards in the chassis, there's several boards in boxes, not in the chassis. These all appear to be home-made I/O of some sort, at some later date I might try to identify what they are.

Thanks for the suggestion about covering the PROMs; fortunately the system has been in a dark garage under cover for a long time, but next time I'm in there (braving the spiders!) I'll cover them. Unfortunately I don't have a ROM reader, I haven't had one since the 90s.
 

wperko

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Jul 4, 2007
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146
Hi,

There are a few affordable devices you can find on eBay to read/write PROMs ... a lot of people have at least a XGecu TL866 II Plus ... it can read and write many PROMs, but another good one is the Willem Eprom PCB5.0C ... it can read/write even older PROMs.
 

twolazy

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If you go with a Willem, (which I love btw), Try to not go with the 5.0 versions. Get a V3/V4 "total usb" version. They are way more stable and dont gotta mess with jumpers/switches.
 

Creator

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Jul 31, 2022
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Hi,

Before taking any more photos, you should cover up the glass on all the PROMs that don't have labels over them. Light erases PROMs.

Good high-resolution photos of each board front and back helps to identify the boards and the revisions of the boards.

Kind'a looks like a Cromemco home-built.
Covering the windows is a good idea. FWIW back in the day I wondered about what it would take to erase an EPROM with sunlight so I placed one in direct sunlight in a window sill. I went on to check it periodically, after about a year I lost interest. Not one check ever showed even a bit changed.
 

ajacocks

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@Creator indeed this is an important thought. There have been a bunch of folks testing what it actually takes to erase and EPROM, and it’s quite a significant amount of UV radation. It’s unlikely that a flash from a camera would affect them immediately, and _very_ unlikely that the ambient light inside of a machine would erase them, in any reasonable time. However, yes, it’s worth putting covers on the windows.

Welcome to the forum!

- Alex
 

wperko

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Hi,

Back about 1975 or 1976 I went to a local demo of home computers at the UofM.

One of the demos was running just fine, with the computer open and the new circuit board sticking up on an expander board a photographer took a photo of the project with a flash. About as fast as that flash went off the demo stopped. The guy couldn't get it running again until he replaced the EPROM on the board. This time he taped over the little window with a piece of electrical tape so future flashes didn't take down his demo.
 

Eudimorphodon

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One of the demos was running just fine, with the computer open and the new circuit board sticking up on an expander board a photographer took a photo of the project with a flash. About as fast as that flash went off the demo stopped. The guy couldn't get it running again until he replaced the EPROM on the board. This time he taped over the little window with a piece of electrical tape so future flashes didn't take down his demo.

Just spitballing, I would guess that there's a chance the EPROM wasn't "erased", it was damaged by photoelectric effects.

(IE, silicon junctions essentially acting like a solar cell when hit with the right/wrong kind of light, which can be generated by things like Xenon flashes. A few years ago people discovered they could crash a running Raspberry Pi 2 with a xeon flash because the surface mount package design of the voltage regulator chip leaked enough light in to cause a power surge sufficient to panic it. Luckily in that case it didn't seem to actually damage the chip, but it is in theory *possible* for it to happen. )
 

Dwight Elvey

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You should also dump the EPROM and disassemble it. It might give some hints as to how it was setup. As was noted earlier, some pictures of the boards may help figuring things out.
Although, I've done it in the past, bootstrapping a system from ground zero is difficult, it is not an impossible task. It is a great way to learn about a lot about what you have.
Dwight
 

wperko

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Hi,

Not just dump the EPROMs, but post those dumps so they can be archived in a few places so the programs/data isn't lost for future users.
 

Teletech

Experienced Member
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Jul 25, 2022
Messages
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That's quite a thing there. Obviously a labor of love by the original creator.
Might as well start someplace, pull all the boards and power up the mains.
Then ideally one would plug in each card in-turn and power them up slowly with a variac.
Clean the heads on the floppy drives if you can get to them, or at least hopefully inspect them to have a chance of disks not shredding instantly.
Hopefully the monitor is composite, if so perhaps feed it a signal from a DVD player or something to see if the monitor works.
Basically break things down into subsystems you can easily test/verify.
You could buy one of these system-on-a-board and use it to check/verify ram and such if you really wanted to do that.
Any O/S disks included?
 

daver2

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Yes, quite a system there :)!

It just looks as though it is the I/O card that is wire wrapped? Are the other cards 'proper' PCBs? If so, do they have any manufacturers details on them?

Have a look through all of the boxes to see if there is any documentation.

As per the above post, you should remove all of the cards. Make sure you have some antistatic bags or boxes to put the cards in safely. Also, before you remove the cards, make sure you document which slots they are currently in...

I WOULDN'T (however) just power up the unit without getting an electrician to check out the mains side of things. This entire system is in a metal case and (if there is a wiring fault) etc. you could find a live metal case - and that wouldn't be good for your health!

I have a PAT tester at home - so I can perform an earth bond check and an insulation resistance check at 250 V. If you don't have a PAT tester, you can check the earth bond resistance with a multimeter that can read low values. If the safety earth of the outlet is bonded solidly to various points on the metal case, if anything goes wrong, the fuse/breaker should blow/trip.

You should also power the machine from a residual current breaker (again, to limit any safety issues).

Check to see if the power supply is a linear one or a switch mode. If it is a switch mode power supply, using a VARIAC will not be helpful. If it is a linear supply, a VARIAC will be helpful (but expensive if you haven't got one).

You will need to checkout the large electrolytic capacitors etc. for signs of leakage or bulging (visibly) and you can check for electrical leakage with a multimeter - all before powering up letting the "black magic smoke" out of the box!

The more testing you can do without plugging into the mains - the better.

Dave
 
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