Congratulations on owning a historic system! I envy you. How's your APL?
I doubt that many of those made it out of Canada.
Looks like a Gates SLA battery made up of X cells 6x2V = 12V. The ones in your unit are probably dried out and sulfated beyond redemption. Fortunately, they're still made:
Congrats! Super, Super rare.
If I may ask, did you luck into it or did you pay dearly
Do you intend to get it running. It's so old it probably has 1702/A UVEPROMS.
Okay, now I'm jealous. Congrats!
On the previous photo you posted: here, you can just see the "Gates" peeking out from the rightmost cell. From the second photo of the battery you posted, I can see that you're in luck--many of these SLA packs used welded connections between the cells; yours are the "slip on" terminals.
Indeed, an on/off switch was nowhere to be found on the MCM/70. To start it, the user had
only to press the start key (on the keyboard) and the computer responded with “MCM/APL” on the screen to
indicate that it was ready for use. To switch the computer off, one typed ■ OFF and pressed the
return key. However, before the computer would be deactivated, the entire contents of
the workspace and the workspace status were preserved in the current state on the cassette.
The MCM/70 user’s guide explains:
"This is to insure that nothing is accidentally destroyed. In order to have the system restore
them [i.e. the workspace and the workspace status] back in the computer at some later date, the
cassette must be mounted in the tape drive before the start key is pressed. If this is done the
computer will automatically reconstruct the saved items in memory to appear as though the
■ OFF function had never been executed."
A unique feature of the computer’s power supply was a power failure protection system,
designed by Edwards. It allowed continuous operation under battery power in the event of
power failure; for extended power loss, the computer initiated an orderly shutdown: it
automatically provided system backup by copying the RAM content to a cassette before it shut
the computer down. The system was automatically reinstated when the power was restored
and batteries were recharged.
According to "The Making of the MCM/70 Microcomputer" (section below) the batteries are integral to the shutdown procedure. I wonder if the batteries are required for the start-up circuit too? Could I just put 12V DC on the two wires that go to the battery pack and try to start it? I have not attempted to plug it in yet. Before even thinking of doing this, I still have to look it over but it was just a thought I had last night.
It might, but with something this rare, you have a bit of homework to do. The first thing is to disconnect the AC-fed power supply from the main board and check its voltages. Since it's most likely a linear supply, you can apply the "bring the line voltage up slowly to re-form the capacitors" procedure. Then you need to check the resistance of the DC feed to the main board to determine if you're looking into a dead short--if so, you need to diagnose and repair that first.
It could well be the case that simply replacing the batteries and plugging the AC cord in that it'll spring to life. But I wouldn't bet my life on it. Take your time with this gem.
A full-blown switching power supply would indeed be unusual in something of this vintage. When this thing was made, I suspect that Bob Boschert was still tinkering with his stuff. Switching regulators, on the other hand were not uncommon.
Interesting in that the system won't start without the internal battery being fully charged.
Turns out that isn't the case. The only thing you will see is a battery Low indicator light. Also, no schematics so that's a bummer but I wasn't really expecting to find any.
If you haven't already, you might want to get in touch with Josh Bensadon; I think you know each other and you're practically neighbours.
He reverse-engineered and rebuilt the MCM-800 at York U (even an emulator), including a lot of time spent on the tape drive and format; I would think that some of his experience and expertise might be useful for the MCM-70 as well, and he might even be able to help you get yours going.
Good luck!!