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Thread: RCA Microtutor

  1. #1
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    Default RCA Microtutor

    https://www.ebay.com/itm/RCA-1800-Mi...%257Ciid%253A1

    I alerted the seller that they were missing the CPU card and ought to mention it but they elected to go with the 'everything you get is in the photos' sidestepper.

    I kinda want it, actually -- but I've not seen the 1801 chips for sale recently and I would assume finding the original card would be probably impossible. I don't think it'd be too impossible to recreate the card itself (probably can even find the right blue soldermask somewhere - that *is* soldermask, right?). But yeah.. I'm guessing the chips would be tricky (and expensive).

  2. #2
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    I got lucky with this complete one last month at a reasonable Buy It Now price before anyone else grabbed it.

    https://www.ebay.com/itm/RCA-1800-Mi...orig_cvip=true

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    Well done! I got lucking on my MEK6800D1.. but can't catch stuff I'm not looking for. Didn't even know the Microtutor existed.

    Yeah, looks like I've bought this one for a fair bit more. Now the hunt for the CPU begins. Are there schematics/artwork for the CPU board around? Hoping I can find a good enough scan or picture of the original board and can just work on making one up.

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    I'll have to check the manual that came with mine. Might be the same manual as in this item listing that is the subject of this thread, just with different cover artwork than the one I have. I'm pretty sure it had a schematic for main board, and CPU and memory boards, and connector pinouts. There isn't much to the CPU board, just the two CDP1801 CRD / CUD chips, a resistor pack, and an electrolytic capacitor.

    Might be rather hard to find the two CDP1801 chips. Maybe a replacement board using a common CDP1802 could be built instead.

    http://www.decodesystems.com/cosmac/#microtutor


  5. #5
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    The manual shown in the item listing is different (maybe slightly earlier) version of this manual:

    MPM-109 RCA 1800 MICROPROCESSOR COSMAC Microtutor Manual

    Appendix 4-A on page 39 (page 45 of the PDF) contains a schematic for the CPU board. The CDP1801CR and CDP1801CU chips are interconnected as in the TA6889 (40-pin CDP1801CU) / TA6890 (28-pin CDP1801CR) data sheet.

    The pull-up resistor pack is a 15 element 22K array, part number 898-1-R22K

  6. #6
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    Quote Originally Posted by falter View Post
    I don't think it'd be too impossible to recreate the card itself (probably can even find the right blue soldermask somewhere - that *is* soldermask, right?).
    I don't think there is any soldermask. The blue color is just color of the PCB.

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    Thanks gslick! That'll help. I found a sort of scan of one side of the board online.. has the chips in the way but I can sort of deduce traces. I did this with photoshop on another board.. scanned both sides, converted to black and white.. inverted and then used threshold.. voila. Just had to do some fixes on some of the traces and airbrush out components. Gonna look around for some better scans. But first gotta try to find the chips. This seller is a consignment store.. might ask them to ask whoever they got it from to check for the missing board.

  8. #8
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    Got a call from the place that sold me the Microtutor.. the original owner found the missing CPU card. Unfortunately rather than handing it over or selling it to me for a nominal amount, he thinks it's worth thousands and wants to ebay it. The store (an ebay consignment place) talked him into holding off and contacting me first.

    What do you guys think? I know the 1801 is collectible, but the only auction I found for one chip was $135.

    Kinda sucks that he's going to be like that. It should have been with the original unit. Now I'm going to have to go into battle with CPU collectors.

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