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  1. Replies
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    The "dead short" might be intentional as probably...

    The "dead short" might be intentional as probably one end of both +5V and +12V secondaries goes to a common negative rail (0V), you're measuring basicly the very low resistance of both secondaries in...
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    I have the habit of never buying NOS chips from...

    I have the habit of never buying NOS chips from China (or other old parts), since I've got fakes or bad parts in the past.
    Today I've ordered a MB7052 TTL PROM from a german seller, for a ridicoulus...
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    I have recently fixed a TTL PROM chip (out of a...

    I have recently fixed a TTL PROM chip (out of a Disk II interface card) that kept on losing pins (iron oxide does that, as soon as the tin plating starts having holes), so if the only problem of the...
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    Thanks all, I've found a person in Italy that can...

    Thanks all, I've found a person in Italy that can do the job. I'll post a followup when it's done, just to let other know.
    Best
    Frank
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    Interesting list, thanks! I might have found an...

    Interesting list, thanks!
    I might have found an Italian guy who has a Data I/O 29B and could do the job.
    I'm looking for a 29B myself since years, but it is very difficult to find in EU (and...
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    Need MB7052 programming service (EU)

    Hi all,
    as part of an arcade PCB repair (vintage cpu board, so kind on topic!), I need a new MB7052 256x4 TTL PROM. I can't program TTL proms with my current programmers (and I've been trying to...
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    Thanks for sharing Hugo! That's highly...

    Thanks for sharing Hugo! That's highly interesting!
    Frank
  8. Well, yes, you should also look at pin 11 which...

    Well, yes, you should also look at pin 11 which is driven by the PET and compare with 9 which is the receive pin of the same line. However NDAC is handled by both UC6 and UC5, so you might try...
  9. The banks are 2, only the $f000-$ffff segment has...

    The banks are 2, only the $f000-$ffff segment has 4 possible mappings. I'm quite sure both basic 3 and 4 are complete and working, since I've just duplicated the image I'm using myself on my 2001 and...
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    Hello! I have designed adapters for 6540 ROMs...

    Hello!
    I have designed adapters for 6540 ROMs and 6550 RAMs myself. I can give you the gerbers to order the PCBs yourself or provide a built and tested one, but that will be expensive mostly because...
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    I completely agree with Dave. It looks like a 510...

    I completely agree with Dave. It looks like a 510 ohms one, but I'd not take chances and just measure the twin one.
    Frank
  12. Or input multiplexers for video ram has shorted...

    Or input multiplexers for video ram has shorted inputs.
    However, since it's not doing that always as the signal appear to get "normal", I don't know what to guess really. Is the frequency of all...
  13. It would be useful to see those signals at the...

    It would be useful to see those signals at the UC3.7 and UB3.3

    Frank
  14. oh, and obviously goes into the motherboard...

    oh, and obviously goes into the motherboard databus also for $8000-$8FFF (because of the video ram).

    Frank
  15. Hi Dave, the version of the RAM/ROM board that...

    Hi Dave,
    the version of the RAM/ROM board that he have, only access the original PET bus from $E800 to $E8FF. ROMs can be selected in 4K ranges (for example, $F000 to $FFFF can be accessed on the...
  16. Hi Dave, your mod looks ok to me. However I've...

    Hi Dave,
    your mod looks ok to me. However I've found more effective to make a little daughterboard adapter to replace these kind of ROMs, so I don't need to modify the hardware.
    Unfortunately, my...
  17. Replies
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    hmm 6.63V isn't really a good sign unless your...

    hmm 6.63V isn't really a good sign unless your multimeter is out of calibration by a large margin. Are these voltage taken with no cables attached to the 1541? All those 0V mean faults.
    It's...
  18. The good thing about 6502 ML is the conditional...

    The good thing about 6502 ML is the conditional jumps don't need any relocation. If all JMP/JSR are labeled, you just change .org directive, add the start vector in the RESET vector locations and...
  19. The daughterboard is actually one of my own...

    The daughterboard is actually one of my own design.
    By the way, if you (daver2) can make a version of your test ROM that can work in the 4K space at F000-FFFF I'd be happy to send a new EPROM image...
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    Yep, a friend has one, so I'll try to make a...

    Yep, a friend has one, so I'll try to make a clone (well, much smaller I hope) of it.
    Thanks!

    Frank
  21. Replies
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    yes also swapping the CIAs on the C64 could give...

    yes also swapping the CIAs on the C64 could give a clue, if something changes. But not all the C64 have socketed CIAs :)

    Frank IZ8DWF
  22. Onboard regulators can only have issues if the...

    Onboard regulators can only have issues if the electrolytic capacitors are dried out. I just suggested you to check the power supply with the oscilloscope in AC coupling (I should have been more...
  23. From what you describe (any signal at all on pin...

    From what you describe (any signal at all on pin 9 of UC7) it must be no ground connection on UC7 socket or very badly regulated power supply (200 KHz ???). That pin is an input.
    Check the UC7...
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    Ok so first of all: what kind of 1541 is it? So...

    Ok so first of all: what kind of 1541 is it? So we look at the right schematic?
    First of all, disconnect the serial cable from the 1541, power it on and check the voltage between pin2 of the serial...
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    If you have only one C64 and only one 1541, you...

    If you have only one C64 and only one 1541, you can't easily tell on what side of the serial bus lies the fault.
    To further diagnose this issue you would need at the very least a multimeter. A logic...
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