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Finally got my MCM/70

snuci

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Nov 22, 2012
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Richmond Hill, Ontario, Canada
I'd love to know if there are any other collectors out there with an MCM/70. Just thought some of you guys might appreciate a quick picture or two after unpacking it. It needs a good cleaning still. It is non-functional but I was expecting that. They are just not easy to find.

MCM70 Before - top.jpgMCM70 Before - front profile.jpgMCM70 Before - rear profile.jpgMCM70 Before - rear.jpg
 

Slob

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Oct 20, 2017
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Kentucky USA
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.
 

snuci

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Congratulations on owning a historic system! I envy you. How's your APL?

If I could get her working again, I'll let you know. I was worried there was a leaky battery in there that may have leaked all over the boards (for the battery backed shutdown) but it looks fine. They will have to go but it was a good design choice to separate them. I just didn't think there would be that many. Clearly, leaky batteries is not the issue.

IMG_20181018_2112360.jpg
 

Chuck(G)

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Pacific Northwest, USA
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:

853.jpg
 

snuci

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I doubt that many of those made it out of Canada.

I actually got this from the original owner from Pennsylvania and it looks like he sold them given the documentation I have.

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:

Thank you. I think you nailed it. Here's a quick pic. They are larger than D cells but not too much, in case anyone is wondering about the size.

IMG_20181018_2143118.jpg
 

Chuck(G)

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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.
 

falter

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Vancouver, BC
Okay, now I'm jealous. Congrats!

How did you even begin to find someone with one of these, in the US no less?
 

snuci

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Nov 22, 2012
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Richmond Hill, Ontario, Canada
Congrats! Super, Super rare.

If I may ask, did you luck into it or did you pay dearly :)

Thanks Slob. Sorry, I didn't see your post initially. The thread notifications are slow and sometimes I don't get them if I am browsing the forum as was the case with your post.

Anyway, I lucked into it AND paid a reasonable sum. I was fortunate enough that the original owner reached out to me via email with two pictures and a description of the system and asked me for an offer. A little research showed that his name was on a list of original known installations noted under Chapter 8. In the past, I have made offers that would be "favorable to me" in terms of existing established value and sometimes they would work while other times it would result in no further communication. I did a little research but I could find no evidence of past sales for the MCM/70 so I didn't know what to offer. I could guess at a lower value and hope the original owner would bite but I could lose the opportunity and I didn't want to lose this opportunity as I am certain it would not come up again (I think the ones remaining are counted with single digits). So I made, what I thought, was a good reasonable offer based on 8008 computers. It was not low but was a little lower than what the seller originally wanted so we settled in the middle. Both of us are happy which is the key.


Do you intend to get it running. It's so old it probably has 1702/A UVEPROMS.

I will make every effort to get it running. Zbigniew Stachniak who wrote the book on the MCM/70 and presented at VCF doesn't know any that are working so it will be a tall task and if I fail, it won't be be disappointing to me. Just having it is good enough for me. Last night I started to take the cover off but I couldn't see the main board. To be honest, I'm not sure where it is as it needs to be further taken apart. I couldn't find the Intel 8008, the upgraded 8k of memory (originally 4k) or the ROMs but the ICs I did see had 1973 dates. I would be certain the ROMs are 1702As as there was some discussion of this "new technology" in Stachniak's book that helped with this project. I just couldn't see the main board when I opened it up and it was late so I just opened the top cover an peaked in. I was shocked at how modern it looked on first impression but it was just a glance. I'll certainly take pics.
 

snuci

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Okay, now I'm jealous. Congrats!

Thanks falter. It really is my "end game" computer and oddly enough, I was already in the process of acquiring an MCM/900 while this email popped up. The MCM/900 is a later model with dual 8" drives and a printer. I was excited just to find this. I was shocked at the MCM/70.
 

snuci

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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.

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.

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.
 

Chuck(G)

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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.
 

snuci

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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.

From what I read, it has a switching power supply but I have to confirm that. The power supply in this computer was controversial in terms of getting it to work when it was first built and could be the case today. I will not rush and am just looking at options right now. In the meantime, I am checking if power supply schematics (or any schematics) are available.
 

Chuck(G)

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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.
 

snuci

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Richmond Hill, Ontario, Canada
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.

I'll take some pictures but the original design was to try to include a switching power supply (link to part of "Inventing the PC: The MCM/70 Story"). Seems that Google books doesn't show all pages in a specific chapter so I'll have to check with the paper copy when I get home.
 

Chuck(G)

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Interesting in that the system won't start without the internal battery being fully charged. Well, you know where you have to begin. :) I'd probably initially test using a DC (14.5V) supply. If the thing really does have a SMPS, it's quite likely that issues will show up there first.

The printer shown in the brochure is clearly a Diablo Hitype. You still may be able to find APL typewheels.
 

MikeS

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Toronto ON Canada
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!!
 

snuci

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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!!

Ah, so it was Josh who did that. I wasn't aware of who helped out there so thanks for the tip. They added a modern switching power supply to the MCM/800 to get it to work. Zbigniew at York U suggests that I go that route if it cannot be fixed and it is non-destructive so perhaps Josh could help with that if he helped them. I am going to do a little exploration first but I will certainly get in touch with Josh. I was going to send my two tapes to York U to decode but maybe Josh can do it, if he would like.

Thanks again. I want to see it run one way or another but hopefully it can be fixed as is. Good to know there are other options.
 
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