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Thread: Commodore Pet 4016 won't read memory

  1. #11

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    Quote Originally Posted by Pet4016 View Post
    I just orded new 4116 3N chips from Bolivia off ebay and a brand new 74LS244 I will try to solder them in next week when they come. Whats the best way to unsolder a chip without wrecking it, just so I dont ruin possibly good chips.
    Use a 700F iron, apply new eutectic, lead bearing solder to a pin. As soon as the whole solder joint is melted, use a soldapult or vacuum to remove the solder. Wait for it to cool to room temperature before attempting another pin on the same chip.

    When you're done, likely some pins will still be stuck. Carefully use that hot iron and a small screwdriver or pick to free up the pins, one at a time again.

    I frequently save pulled RAM chips and reuse them in sockets. I find that some old RAM chips work better than some 'new' ones.
    Be polite and I may let you live.

  2. #12
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    DM and SN devices 'should' be the same - they just indicate different manufacturers. SN is Texas Instruments. Functionally they are the same device. What will be slightly different is that the SN device will probably be a modern device and the manufacturing process will have changed resulting in a slightly faster device than the original. In your application it shouldn't matter - but in a timing critical design it may.

    Dave

  3. #13

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    Does the PET have a way to override the on board boot,
    like the KIM-1 does.
    I wrote a RAM test for the KIM that the code runs completely in
    the processor and only runs the test on the RAM.
    I displays fails on a single LED tied to a port. It does a blink code
    for the failure. It doesn't look for address failures as it is not all
    that fancy, running out of only 4 registers.
    Although, it was written for static RAM, I suspect it runs fast enough
    to do dynamic RAM for stuck at issues.
    This is a much better than piggie-backing or unsoldering and socketting
    everything.
    At worst, it requires blowing an EPROM.
    Tinker Dwight

  4. #14
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    Quote Originally Posted by Dwight Elvey View Post
    Does the PET have a way to override the on board boot,
    like the KIM-1 does.
    Hi Dwight,
    On the 4000/8000 series PETS, there is a signal called 'NO ROMS' which can be grounded and will disable all on-board ROMs. However the boot EPROM would have to initialize the CRT Controller (6545) to bring up the screen. It would only involve setting up the 16 CRT Controller registers with the proper constants before running the diagnostics. The expansion port connectors (J4/J9) could be used to interface a breadboard containing the new EPROM. For booting, the $FXXX area of memory would have to be decoded from the upper address lines for use as a chip select as the signal SEL F is not brought out to the expansion port.
    -Dave

  5. #15
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    Quote Originally Posted by dave_m View Post
    Hi Dwight,
    On the 4000/8000 series PETS, there is a signal called 'NO ROMS' which can be grounded and will disable all on-board ROMs. However the boot EPROM would have to initialize the CRT Controller (6545) to bring up the screen. It would only involve setting up the 16 CRT Controller registers with the proper constants before running the diagnostics. The expansion port connectors (J4/J9) could be used to interface a breadboard containing the new EPROM. For booting, the $FXXX area of memory would have to be decoded from the upper address lines for use as a chip select as the signal SEL F is not brought out to the expansion port.
    -Dave
    Or you could temporarily cut the trace to the F ROM /CE, insert your diagnostic EPROM into either the A or the 9 socket with the /CE pin bent out and jumpered to the appropriate F pin on the ROM select IC (and a similar lifted pin and jumper to bypass the /NOROM signal if it's a 4000/8000 series and you've enabled /NOROM to isolate the other ROMs).

    m

  6. #16

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    Given some thought, one should be able to just pull the Boot ROM and substitute
    it.
    As for display, there must be a port someplace one could hang a resistor and
    LED off for the blink code. 8 LEDs would be better.
    It doesn't have to be a separate board like I did for the KIM.
    Having the monitor would be better but I'm not sure how much more could be
    done with only the three registers and temporary storage in the stack pointer.
    Coding is quite restricted. I guess with a 1K ROM space something could be done.
    I didn't think I could do the KIM version until I sat down and tried it.
    Looking at the code now, I see one could write a march-C test. It is one of the
    best RAM test out there. I covers all the faults that a galpat covers and much simpler
    to write.
    Dwight

  7. #17
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    Quote Originally Posted by Dwight Elvey View Post
    Given some thought, one should be able to just pull the Boot ROM and substitute
    it.
    Unfortunately the 'Boot ROM' (Fxxx) is soldered in place in all models except the early 2001.

  8. #18

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    Quote Originally Posted by MikeS View Post
    Unfortunately the 'Boot ROM' (Fxxx) is soldered in place in all models except the early 2001.
    Now why would they go and do that? What a bunch of poos.
    Dwight

  9. #19

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    My late 2001N doesn't have soldered ROMs.

    From Commodore's perspective, by the time 4.0 ROMs were mature, it made perfect sense to solder them in. They weren't going to produce another, and both cost and reliability were benefited from soldering the ROMs.
    Be polite and I may let you live.

  10. #20
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    Quote Originally Posted by KC9UDX View Post
    My late 2001N doesn't have soldered ROMs.

    From Commodore's perspective, by the time 4.0 ROMs were mature, it made perfect sense to solder them in. They weren't going to produce another, and both cost and reliability were benefited from soldering the ROMs.
    The early -Ns were certainly socketed but I was under the impression that the later ones were soldered; this one looks like they're soldered but it's not very clear:
    http://www.vcfed.org/forum/attachmen...6&d=1494568660

    In any case, the ROMs in the one we're dealing with in this thread are almost certainly soldered in with the exception of the 'E' edit ROM.

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