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Vintage computer fun

I’ve been kind of following that, there are a lot of YouTube videos e.g. this from Adrian Black:


A fair amount of progress has been made since in turning them into a useable 8 bit machine, folk even porting games to them etc. The build quality seems surprisingly good, though without any real historical context or broad software library they are at best a niche interest. It has been fascinating seeing how innovative the wider retro community has been in getting them to do something useful though. Some exceptionally bright people out there!
 
I hope it is OK to post this link.

Forr Apple ][ GS owners a new accelerator card that I have been following which is now back in pre order; I have ordered for myself as I have ROM1 and ROM3 GS'.

More info https://www.applesqueezer.com/blog

There are some great vids on youtube this being the latest update:

 
A nice article and a film link to how the EDSAC was programmed, by no less than Maurice Wilkes himself.
hackaday.com

Programming 1949 Style!

What was it like to program an early digital computer? [Woven Memories] wanted to know and wants you to know, too. [Maurice Wilkes] and his team wrote a book about their EDSAC and the 18 instructio…
hackaday.com hackaday.com
 
Well, my son came across this in a junk shop, so i've got a new old toy to try and get working. A compucorp 625 mark II

GInWtFa.jpeg


I've tried to find info on this, but there is little about as far as I can see. It's i'm guessing early 80s vintage, and has a nice looking backplane with slot in cards, and in this case a 5 cards (floppy controller, main CPU board, memory, video and printer)

ZNWRalu.jpeg


Here's the processor card. Simple, dual layer, through hole stuff, easy to fix if there's a problem. Z80 at the bottom, TMS5501 at the top, doing keyboard scanning duties.

oY1aHKD.jpeg


So my guess is it's a CP/M machine. It's fuse has blown, so i'll be taking it apart and working out which capacitors are junk.

There are some monsters under the printer:

asFhAK7.jpeg


gulp
 
Wow, that looks pretty cool! Not something I know anything at all about! I imagine the disk drives will be absolutely filthy facing upwards like that!

PS Bet the big caps are fine! Looks like a linear PSU judging by the size of them, so bringing it up slowly on a variac/dim-bulb is likely fine.
 
Cesare said:
Well, my son came across this in a junk shop, so i've got a new old toy to try and get working. A compucorp 625 mark II

GInWtFa.jpeg


I've tried to find info on this, but there is little about as far as I can see. It's i'm guessing early 80s vintage, and has a nice looking backplane with slot in cards, and in this case a 5 cards (floppy controller, main CPU board, memory, video and printer)

ZNWRalu.jpeg


Here's the processor card. Simple, dual layer, through hole stuff, easy to fix if there's a problem. Z80 at the bottom, TMS5501 at the top, doing keyboard scanning duties.

oY1aHKD.jpeg


So my guess is it's a CP/M machine. It's fuse has blown, so i'll be taking it apart and working out which capacitors are junk.

There are some monsters under the printer:

asFhAK7.jpeg


gulp
Click to expand...

Best I can find is from here: https://archive.org/stream/sim_comp..._2/sim_computerworld_1979-01-08_13_2_djvu.txt

https://archive.org/details/sim_computerworld_1979-01-08_13_2/page/72/mode/2up?q=Computech (Page 73)

"[L]OS ANGELES — A desktop computer in-
troduced by Compucorp incorporates in a
single package a CRT, memory and hard-
copy peripherals that are usually packaged
separately

Named the 625 Mark II, the system is
aimed at scientific and business users


The 625 Mark II is based on the Zilog, Inc
Z80 central processor and is offered with an
extended Basic language operating system
and up to 60K bytes of internal random-
access memory (RAM). Dual flexible disk
drives, which can be used for both program
and data storage, store up to 630K bytes of
data, the firm said.


The unit contains a 1,280-character CRT
as well as a 40-column alphanumeric matrix
printer. The printer can provide multiple
copies on plain paper and features variable
character sizes, Compucorp noted.


Five board slots are provided inside the
unit for a variety of interface options,
according to Compucorp. The system can be
used as an instrumentation controller by in-

[...]

serting the IEEE-488 bus option or any of
four other controllers.

Other interfaces include an analog-to-
digital/digital-to-analog interface with an
internal multiplexer and a 32-line parallel
interface. A dual serial communications con-
troller is also available.

Prices for the 625 Mark II start at $8,000.
Compucorp is at 1901 S. Bundy Drive, Los
Angeles, Calif. 90025. "


The only other thing I know is it made in 1977, seems to have been used a lot in the scientific community and used an OS called Zebra.
 
Thanks for that! That's the most info i've seen so far on the machine. There's bound to be a 625 mark II owners club still running them somewhere :)

I've discovered it's all 1978 date code components and the transformer is dated then too. It has switchable modes to cover UK and US mains, and most of the case is fibreglass, which seems to have done very well, except the finish on one side has deteriorated leaving just a smooth surface.

The rust on the front panel around the keyboard will I reckon treat and will respray fine. The disk drive is mounted to a rusty steal bracket, but that looks to be the extent of the rust in the case.

Yes, those vertical mounted drives were a dumb idea. One seems to operate, the other the gate doesn't really work, so that'll need some attention.

Once i've got a suitable 2A fuse installed (it's one of those weird 3AG sized ones) i'll try on a dim-bulb as I don't have a variac. I keep meaning to track one down, but they seem to be hard to come by, and certainly I haven't seen a sensibly priced second hand one.
 
What cards are in it? One is obviously the processor you’ve posted, one is a disk controller. I assume you have some RAM and something for the printer, maybe an I/O or display card too. I’d pull them all out and just power-up the back-plane, that way you can check voltages etc without frying anything. Then introduce them gradually starting with the processor and RAM. You could certainly leave the printer and disks out of the equation until you’ve got some activity.

Another good tip I’ve seen retro computer folk do, but it assumes relevant pin-out knowledge, is to check for shorts to ground on the plug-in card pins before powering them. That way you can often find shorted tantalum caps etc without releasing the smoke.
 
Tony L said:
The Electron was a hugely cost-cut and sadly rather nobbled BBC B for the home market. It has 32k RAM, but can only access it at half the speed of the B, plus it lacks the very useful ‘Mode 7’ Teletext resolution which used way less RAM than other modes (the video uses main system RAM, which is not plentiful). IIRC BBC Model As were 16K RAM, the Bs and Elk 32, and the Master 64.

45894865781_e2ff1f2a20_b.jpg


(case open, top keyboard section to left, bottom section to right)

The interesting thing about the Elk is its (for then) large scale integration. It has a huge Ferranti-made ULA that contains a fair bit of a BBC B in a single device. They apparently had real issues fitting it to the main board, hence there being several revisions. This one looks to be a very early one with a socketed ULA and OS chip (Issue 2 mainboard). One surprise with the Elk is it has a very good keyboard, really substantial with a metal back-plate. I suspect it is just a smaller (no function keys etc) variant of the BBC Micro.
Click to expand...
Reminds me of Nordost Super Flatline cable, although not identical.

P5JCHWI.jpeg
 
Excellent. The post-BBC-era Acorn machines suffer so badly from battery corrosion it is always great to hear when someone saves one. Any otherwise mint, boxed ones sitting in people’s cupboards, lofts etc are just eating themselves to the point repair is a nightmare. I think I’ve linked this video or a similar one from the same channel upthread, but this is an incredible repair. Anyone else would have taken one look and scrapped it as a parts machine. I’ve so much respect for folk with the skill, patience and time to do this stuff.

 
Tony L said:
Excellent. The post-BBC-era Acorn machines suffer so badly from battery corrosion it is always great to hear when someone saves one. Any otherwise mint, boxed ones sitting in people’s cupboards, lofts etc are just eating themselves to the point repair is a nightmare. I think I’ve linked this video or a similar one from the same channel upthread, but this is an incredible repair. Anyone else would have taken one look and scrapped it as a parts machine. I’ve so much respect for folk with the skill, patience and time to do this stuff.

Click to expand...
Just been watching GadgetUK. One of my favourite channels.
 
I've removed the two drives - the slide grease for the locking mechanism has gummed up, hence the mechanical issues one was having. Underneath is the voltage regulator board, and it's a bit corroded and has an obvious hot capacitor:

E15B8fS.jpeg


There are 4 transistors at the back which obviously get pretty hot, and i've not seen them yet, or stuck a component tester on them, but i'll do that next:

S2ZAnue.jpeg


The boards in the unit are (in order towards the back of the chassis):

1) Floppy controller card
2) Processor card
3) memory card
4) video card
5) printer card

These all look reasonable, but I think it's sensible to disconnect the lot when first powering up.
 
Lots of cleaning needed! Looks rather corroded towards the bottom of the board, hopefully that will clean up. Most of the little caps look to be ceramic so far less risk on power-up than tants. I’d still check voltages etc with it empty and then try booting a minimal config of processor, RAM and video card.

What sort of keyswitch mechanism does the keyboard have? Hopefully not foil & foam!

PS You look to have a free washer on the left side of the heat sink!
 
At home I had various BBC micros and various Atari STs before my first PC. This is still in a cupboard:

vuDkZTf.jpg


When I started in computing we had DEC PDPs with 8" floppy discs. Most of our coding went onto punch cards using a desk hand punch or the office punch card machine the size of a piano which had keyboard for creating punch cards. Paper tape was also used. IBM PCs and desktop monitor networks came at a later date.
 
Tony L said:
Lots of cleaning needed! Looks rather corroded towards the bottom of the board, hopefully that will clean up. Most of the little caps look to be ceramic so far less risk on power-up than tants. I’d still check voltages etc with it empty and then try booting a minimal config of processor, RAM and video card.

What sort of keyswitch mechanism does the keyboard have? Hopefully not foil & foam!

PS You look to have a free washer on the left side of the heat sink!
Click to expand...

I think given the board is simple double sided stuff, even with some corrosion it will either clean up or be easily repaired. Good spot on the loose washer, that's probably been in there 40 years :)

The keyboard has mechanical contacts - if you pop the covers off, you can see a pair of metal pads which move together to touch when the key is depressed, so i'm guessing there are some springs in there too. A bit of contact cleaner and hopefully all will be well!
 
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