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Thread: Commodore 16 won't boot - what next after replacing the TED

  1. #1

    Default Commodore 16 won't boot - what next after replacing the TED

    About 6 months ago I got hold of a C16 which was sold as having a faulty PSU and system unit untested.

    The PSU was quickly fixed (just a loose wire) but the machine failed to boot, it just displays a coloured screen.

    At the time the TED was thought the most likely fault. I bided my time and waited for a reasonable priced one to come up on ebay and I've bought one which was sold as tested and working.

    It makes no difference. Assuming this TED actually does work as described, where do I go next?

  2. #2

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    RAM or buffers, if the machine has suffered a PSU failure, RAM ICs and the related glue logic are prone to fault.

  3. #3

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    Thanks for the reply.

    There are quite a few MB81416-12 RAM chips on ebay which I could source. Is the other markings on the chip significant (existing chips have '8423 V23' on them, the ones I'm looking at have '8738 T25')? Will the replacement chips 'piggyback' for testing before desoldering the old ones?

    And what would the buffer chips be?

  4. #4

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    The "buffers" are the multiplexers used for the address lines, at least in other machines are a common fault.

    The piggyback trick has been always useful to me, in fact I keep a machine with a good chip piggybacked due the extremely bad state of the PCB, too risky to desolder the bad original IC. I just keep only a rule of thumb in my mind, if the chip is HOT, don't piggyback. If a RAM chip is too hot to touch it's probably faulty and worth to replace.

    Just one more thing, have you checked the voltages and are your sure the repaired PSU is giving you correct values?, it's always a risk to plug a good chip in a not working PCB as it can be a chip-killer. Check the 5V line first.

    There're usually a pair of documents extremely useful to repair these machines, one is the schematics and the other is a troubleshooting guide. Here're the C16 ones:

    C16 Service Manual
    plus-4 & c16 Ttroubleshooting

  5. #5

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    I would try replacing the CPU.

  6. #6
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    Quote Originally Posted by noppa View Post
    I would try replacing the CPU.
    +1. I repaired two Plus/4s that were black screen and both turned out to be the CPU. It seems it is very unreliable.

  7. #7

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    Quote Originally Posted by Zippy Zapp View Post
    +1. I repaired two Plus/4s that were black screen and both turned out to be the CPU. It seems it is very unreliable.
    I got 4 Plus/4 and 4 C16 and just ONE cpu working!

  8. #8
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    can you post a screen shot of the 16 that does not initialize properly. I can tell by the screen sometimes what's what.
    @ BillDeg:
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  9. #9

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    Quote Originally Posted by Zippy Zapp View Post
    +1. I repaired two Plus/4s that were black screen and both turned out to be the CPU. It seems it is very unreliable.
    Yep, and harder to find than the 6510 and of course, not cheap.

  10. #10

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    Quote Originally Posted by jltursan View Post
    Yep, and harder to find than the 6510 and of course, not cheap.
    This could be useful :

    http://hackjunk.com/2017/06/23/commo...pu-conversion/

    http://www.webalice.it/gratteri/65028501.html

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