View Full Version : Mark 8 variant

Roland Huisman
April 6th, 2014, 10:34 AM
Hello everyone,

I've bought an old Mark 8 computer. The man used the original Mark 8 boards but he built his own version.
He made all the boards pluggable. And he added some memory cards and designed a video card for it.
He did not use the LED display but used several 7 segment displays for the read-out. He also made a programming remote.

I think he did a really nice job back in those days.

I haven't tested it because I want to readout the EPROM first. There is only one EPROM
but if this one is distroyed the complete machine will be useless I think.
So I really hope the EPROM still has his program intact. It's a C8702A version :huh:

18171 18172 18173 18174 18175

Roland Huisman
April 6th, 2014, 10:36 AM
And a few more pics...

18179 18178

Regards, Roland

Roland Huisman
April 7th, 2014, 02:25 PM
Does anyone have a datasheet of a C8702A EPROM?
I have no idea how to read this thing. Is it electrically the
same as an 1702A?

Thanks in advance for your info!

Regard, Roland

Frank S
April 7th, 2014, 10:47 PM
Hello Roland,
yes it is equal to the 1702A.
I have a reader/programmer for that EPROMs.
Here (http://www.dvq.com/docs/1702pgmr_pe_78.pdf) is a DIY programmer and here (http://www.tronola.com/html/1702a_prom_programmer.html) some other info.


Roland Huisman
April 9th, 2014, 03:50 AM
Hello Frank,

Thanks for your information! I've got the PCB, CPU and instructions
for the Marting Eberhart programmer. According the website you mentioned,
the programmer from Martin should support the 8702. But Martin told me he doesn't know...

Martin asked me for a datasheet to check it. But I can't find it either.
It should be somewhere I hope...

Regards, Roland

Roland Huisman
April 30th, 2014, 08:06 AM
I have powered up the Mark 8. First without cards, everytime added
one single card, checked for heat and measured the power voltages.
Everything was fine until the mainsfilter blew :-) So I bypassed that one for now.

I have waited with the eprom. When the Eprom data is saved I will put that one in.

I assume the Mark 8 should work without the eprom, but it's not for sure.
I can examine memory and the address counts one up. But I can't write anything in memory.


I was wondering, how good is the quality of these wirewrap connections?
The silver turns black at many wires. Is it wise to solder all these joints?
Any experiences? The whole backplane is full of wirewrap connections.


Regards, Roland

Frank S
April 30th, 2014, 09:13 AM
...I was wondering, how good is the quality of these wirewrap connections?
The silver turns black at many wires. Is it wise to solder all these joints?...

Hello Roland,
WireWrap connection are generally long lasting.
The wire what is wrapped round the post is gas tight connected with the post.

Have you ever try to get solder float on older (black) silver coated wire and the posts? No chance!
Silver coated wire, which has a massive oxide coating tends to break easily.
When this already happend with your backplane wraps, i think the best is to rewire it again with wirewrap connections.


Roland Huisman
April 30th, 2014, 10:23 AM
Hello Frank,

The machine has been stored for about 25 years in a horrible environment.
The topcover was completely rusted. The wooden panels inside were mildewed.
And note the huge amount of dirt between the cardholders...

18543 18544 18545

So I began to wonder how the quality might be from the wrapped joints on the connectors.
When I have placed the eprom back again I can tell more about it's function (I hope...)
And maybe there are some functions like deposit which would work. But I don't think
it has anything to do with the eprom.

I guess there is a tapeloader inside the eprom...

Regards, Roland

Roland Huisman
May 19th, 2014, 01:25 PM
Hello Everyone,

I've got my Mark 8 up and running. (for so far)

The remote was defective. There were only three zeros in the display.
I could not put a value into the display. In the meanwhile I've got a lot
of the original documentation of this machine. Including the Radio electronics from '74.

I began to draw the schematics from the remote. While I was half way I found
an NE555 which was used as a clock generator. But no clock signal. After replacing
the NE555 I had a clock again. But the panel did still not work.

Eventually I ran into a circuit around a 7474 which seems to be broken.
After replacing this 7474 the remote came back to live :D:D:D

So now I can read and write into each memory location. Still a lot to figure out.

18753 18754 18755 18756

Defects fixed until now: NE555, 7474, mains noise filter.

This machine is inspired by 'the digital group' from Robert Suding.
Many (MANY!) original 'the digital group' documents are includes with the machine.
The octal input however is completely different than the circuit from 'the digital group'

Further, the machine is quite well documented by the brothers Henk and Jaap Berkhoudt
who both made this machine in their youth...

Regards, Roland

May 20th, 2014, 02:45 AM
Very cool. Welcome to the wonderful world of managing H&L registers by hand...

You should be able to use most of Mike Willegal's Scelbi software with minor modification. http://www.willegal.net/scelbi/apps8008.html


Roland Huisman
May 23rd, 2014, 02:29 PM
Hello Corey,

Thanks for the link! I have to figure some stuff out. The machine has 14K of memory.
So that should give some possibilities :-)

And I've got also these books (and more). Games for the 8008. :D


The constructor of the computer really enjoyed the
pictures of the machine working again for so far.

He told me they ran moon lander on the machine once.
There is a complete book of scalbi basic with the machine.
There are some notes in it because of different I/O addresses.

Regards, Roland

May 28th, 2014, 07:46 AM
Most SCELBI software that I have seen doesn't include I/O drivers. For example the Galaxy program is listed as 4K, but doesn't include any I/O software at all. I had to work pretty hard on tweaking it in order to make it fit in 4K with the added and necessary I/O drivers. A lot of the early/mid 70's home computer gear left a whole a lot to the user to figure out. This is very different than what we are used to with todays canned solutions for everything.

If you come up with any additional 8008 software, I'd be more than glad to host it on my 8008 software page.

Mike W.

Roland Huisman
June 11th, 2014, 03:12 AM
Hello Mike,

When I have time I will try to sort things out. There are many documents
that came with the machine. Probably a nice winter project.

An other thing is that my scanner is not supported under windows 8.1... That's also for
the winter. Maybe I will buy a new and faster one... Than I can scan the documents.

Regards, Roland