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Restoration of a Motorola MEK6800D2

N

nijssen

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Oct 12, 2021
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The Netherlands
I recently got a Motorola MEK6800D2 machine from the late 70s that I want to restore. Think it would be fun to make a (slow) work log of this in this thread.

Here I share some (before) pictures. It is very much complete with manuals and sits in a nice enclosure. I also noticed an SWTPC memory expansion board, maybe these were used in the SWTPC 6800 machine as well, have to look into this. It is full of dust, but no rust. It seems to be well used and has an unusual round I/O connector wired up. Any ideas of the brand and type?

My first step will be to get everything out of the case carefully and clean this. Will start with testing the power supply in isolation. The manuals and binder are also very much aged and dirty, they need some cleaning as well.

Tips welcome, stay tuned!


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I didn't realize they had a case. Are you sure the case wasn't a homebrew thing? I'll bet that memory card was hand wired in there. Really clever though.
 
I had a D2 (back in the day) with the addition of a couple of DACs to generate analogue voltages (X and Y driving of an oscilloscope, 'music' or driving analogue theatre light dimmers from Rank Strand etc.).

My first 'computer'...

I don't remember an 'official' case either.

Shout if you need any help with fixing it. Yes, I like the addition of the memory card also.

Dave
 
Great find! Motorola never produced a case, lots of homebrew cases/enclosures though. Mine was plywood - rough but functional.
Originally only available in Kit form, with ICs, keyswitches, discrete components etc. no power supply. Motorola branded exorciser (86pin bus) memory cards were hugely expensive back in the day, most of us hobbyists adapted cheaper s-100 memory cards or SWTPc cards, or build our own memory expansion. Here are bare PCB photos from one of my unbuilt kits - useful for debugging/tracing lines under sockets and locating any possible modifications by the original owner. I have spare JBUG rom and other parts if you run into issues. Restoration will be a rewarding project. The D2 design is quite amenable to modifications and expansion possibilities - a great base. Used mine (expanded w/TVTtypewriter video out and RS232) for home "automation" in the late 70s/early 80s. Still tinker with several versions including the original.

MEK6800D2-front.jpgMEK6800D2-Back.jpg
 
Bruce Tomlin said:
I didn't realize they had a case. Are you sure the case wasn't a homebrew thing? I'll bet that memory card was hand wired in there. Really clever though.
Click to expand...
I recall there being 3rd. party cases for the D2. It was a popular starter system.
The SWTPC memory.... I think that was a one off project.
 
So I took the whole thing apart, did not power it up yet. Discovered the big round connector to be a Hirschmann brand, type unknown. The power supply (only +5V) is in a bad shape, thinking about redesigning a new regulator board that fits the case. Any tips? Can also use a new Meanwell, but then this thing loses its spirit. Transformer seems solid. The fuse was 'solid' as well but lost its purpose by the previous owner, hmm. I also cleaned the documentation and fixed the binder. @daver2 found a document Analog-to-Digital Conversion Techniques with the M6800 Microprocessor System, does that ring a bell? ;-)

The memory board is an SWTPC MP-M (see here), think it has 4KB. It only uses +5V, handy. The case is homebrew, the holes for the keyboard are nicely milled, the rest is made by a regular drill. I like the 'Altair' color. Thinking about having some fun with the Dremel and repainting the whole thing (the case I mean). Any ideas how to find the 'original' color?

Next step will be to power up the mainboard and the keyboard with the bench supply. If it has any life this project can start off :-).

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One caution: The MEK6800D2 requires a single +5 volt power source; however, the added SWTPc MP-M memory board requires 8 volts DC for the on-card regulators to work properly.

This may explain that perforated board shown above.
 
Did someone say 86 pin connector? Some of the boards I've been documenting plug into an 86-pin card edge connector...

here are part numbers to help track down NOS or modern equivalents: EDAC 737-086-540-206, TE/AMP 2-119254-9, TE/AMP 7-119254-9
 
Vermithrax said:
One caution: The MEK6800D2 requires a single +5 volt power source; however, the added SWTPc MP-M memory board requires 8 volts DC for the on-card regulators to work properly.

This may explain that perforated board shown above.
Click to expand...
Yes I realized that, think the DC was fed to the memory board before the big 5v regulator (and after the rectifier of course) on the hobby-supply. If I create a new regulator board I could do the same…
 
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