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Tales from Midibob's workshop Maygay MMM


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Definitely not factory mods!

 

The 10K resistor appears to be an attempt to shorten the reset period, or boost a dodgy T61

Edited by Wizard
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I believe everyone should have access to schematics, they are virtually essential for accurate emulation and might even save some old machines from being scrapped. It does nobody any good hoarding them.

Edited by Wizard
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Last thing yesterday I tried firing the board up with the reel deck and ......nothing!

 

After a bit of head scratching this morning I tried the ROMs in another board and they didn't do anything in that one either?

I then realised that as the files were only 2k they needed to be burnt in the upper part of the 2732 ROMs. I knew I should have made a note about it last time I did it. :headache: 

So in goes another set and bingo, the reels index.

 

Next thing is to start testing functionality which I'm hoping won't be too bad as the board is in fairly good condition.

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I believe everyone should have access to schematics, they are virtually essential for accurate emulation and might even save some old machines from being scrapped. It does nobody any good hoarding them.

could certainly use the help of one with my MPU2's (4 dead, one working)

 

My thoughts exactly. Pity the some of the manufacturers don't feel the same.

tried e-mailing Barcrest in December asking after a MPU2 schematic - didn't get a reply - not sure if the address I used is still current (info@barcrest group.com) - does anyone have an alternative line of enquiry I could try?

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After a bit more messing about and overlooking the switch matrix info that was in the manual I can now operate the start button and as far as I can tell it all looks good.

Just one last mod which I'm not happy about and that's the two parallel wirewound low Ohm resistors which have been added to the board (top middle). They connect the OVL and OVH (low and high voltage grounds). However according to the diagram this is done on the PSU by R93 although there's no value mentioned? They aren't on the other board I looked at so I've no idea why they are there. They do look a bit more professional than the other mods so I'd like to hear from any other MMM owners.

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  • 3 years later...

I have a couple of MMM boards in at present which both work (almost) but I haven't been able to test them fully as I didn't have a reel deck. The nice thing with this old tech is the board bolts on the back of the reel deck so it is a contained unit. With other techs that I don't have reel decks for, which is most of them, I use my Arduino to emulate it. So far this has worked admirably but the MMM was a no go. Most other techs as long as it thought the reels had indexed it didn't care about reel position. Not so with the MMM. It needed to know exactly where the reels were. Also most reel sets have just one tab for the index, others an extra ring of tabs for the counter but for all intents and purposes you could ignore this.

Now the MMM has two rings of tabs and they both have 8 tabs placed around the reel. There are 4 positions where they line up (synch tabs) and the rest don't. In the end after a couple of weeks writing code and getting nowhere I decide to emulate the all tabs in software and blow me it only worked.:D

I have to say I'm not a coder by any stretch of the imagination and for the guys that worked out MAME and stuff would think this was all a bit childs play. For me though it was absolute heaven so I thought I'd blow my own trumpet.

One board I know I've sorted but another has a lamp fault where all the lamps eventually go out. It's a wierd one that's for sure and will be documented here when I get to the bottom of it.

Watch this space......

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