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Type: Posts; User: iz8dwf

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  1. Replies
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    When I had to change C51 (because the tantalum...

    When I had to change C51 (because the tantalum failed short-circuit), I always opted for a 1uF ceramic as replacement. I think a regular aluminum electrolytic should work there unless it's really of...
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    smells like damaged PCB tracks and/or hole...

    smells like damaged PCB tracks and/or hole metallization damaged making no contact to GND on pin 1 of the 555 and/or surrounding capacitors.
    Solder iron is the worst enemy of any vintage repair.
    ...
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    Unlike any other ROM/EPROM I can think of,...

    Unlike any other ROM/EPROM I can think of, MK36000 have "edge activated" /CE. It means you can't read such a ROM by simply pulling /CE low and cycling through the addresses, waiting for the access...
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    With a logic probe, you would first check the...

    With a logic probe, you would first check the clock output from the VIC to the CPU, then check the reset signal to the CPU, then check all the enables on the ROMs and that would tell you if and how...
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    Thanks :) I was feeling so bad for those C64 @...

    Thanks :) I was feeling so bad for those C64 @ 14V :)
    Frank
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    398

    I wonder why 14V AC. The original C64/C128 PSUs...

    I wonder why 14V AC. The original C64/C128 PSUs have 9VAC output, usually it's around 10-11V max. All the C64 "breadbin" boards have an additional LM7805 linear voltage regulator, feed by the 9VAC...
  7. Thread: 8032 CRT issue

    by iz8dwf
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    26
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    1,002

    Have you checked the rectifier diodes in the...

    Have you checked the rectifier diodes in the monitor's PCB? The big smoothing capacitor? The 18V linear regulator?
    These are absolutely the first steps in any kind of repair job.

    Frank
  8. Replies
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    526

    Yes I've found out the documentation for my 2 x...

    Yes I've found out the documentation for my 2 x 80col/64k expansions, they're really only meant for the IIe "special" slot 3.
    Does anyone want to swap? :)
    I can also make my own cards, I just need...
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    Thanks a LOT!! I downloaded the disk image!

    Thanks a LOT!! I downloaded the disk image!
  10. Replies
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    239

    Sunshine IC tester info?

    Hi all,
    I've got this old Sunshine IC tester, I believe it was used in a IIe, now long gone.
    Does anyone have any information about it? A copy of its software would be very welcome of...
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    526

    It turns out that it was only the 7408 on...

    It turns out that it was only the 7408 on position B11 not making a good contact with its socket, too easy so far. The machine now beeps, prints Apple ][ on top of the screen then goes on a prompt ]...
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    526

    This board (rev. 7) has a 555-based reset...

    This board (rev. 7) has a 555-based reset circuitry on the motherboard and it works, so the 6502 definitely gets a reset pulse, but looks like something is really preventing it to execute much. I've...
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    526

    Thanks a lot for the answers! That's good, so I...

    Thanks a lot for the answers! That's good, so I can leave the keyboard disconnected until I make it behave. Another question then: with no add-on cards, what am I supposed to get on the screen on a...
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    259

    Yes I agree, I thought about that later. The chip...

    Yes I agree, I thought about that later. The chip was probably cracked and the first thermal expansion, split the case in half. Replacing that chip resulted in a fully functional PET.

    Frank
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    526

    Apple ][+ with no keyboard?

    Hi all,
    sorry for the stupid question but I haven't seen many of these in my life (yet). Can an apple ][ europlus (rev.7 motherboard) start normally with no keyboard attached? I mean with the flat...
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    What was the actual fault? I've never "recapped"...

    What was the actual fault? I've never "recapped" anything unless the actual capacitors are bad (high ESR, leakage, etc) OR they're the RIFA with cracked epoxy (or about to crack anyway).

    Frank...
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    53976

    53976
  18. Replies
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    Curious 2001N fault

    Hi all,
    I've just received a 2001N (32k, Basic4) PCB to repair. The owner said it was working for few seconds, then the cursor disappeared and after that, it just displayed the usual garbage screen....
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    One more "hint" from the datasheet: The 3.3V ...

    One more "hint" from the datasheet: The 3.3V VCCINT power supply must be at least 1.5V before 5V signals are applied to the I/Os.
    Now, imagine a connected device to an Apple II where the 5V is...
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    891

    Well... I've never been so lucky as you are...

    Well... I've never been so lucky as you are whenever I started pulling chips as an attempt to repair something. You know, the chance is that you introduce hidden problems. C64 pcbs are of rather low...
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    672

    Yes I've read it and sincerely it doesn't add any...

    Yes I've read it and sincerely it doesn't add any clue at least to what I know.
    My totally unproven theory is that those CPLDs have a bit of "datasheet confusion". I mean, if absolute maximum rating...
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    Well, unfortunately 5.5V is a bit on the edge....

    Well, unfortunately 5.5V is a bit on the edge. This particular PSU was sent to me because it seems the only thing that could have damaged two "FloppyEMU" boards. Unfortunately I haven't yet found a...
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    891

    I have that test too, but I've used only on a...

    I have that test too, but I've used only on a very few occasions, so I don't remember if it tests the ROMs. However, if it does, obviously the Basic ROM's select (pin 20) should be pulsing low when...
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    Well, surely I'll try the "real" load, once I...

    Well, surely I'll try the "real" load, once I make some more tests.
    However in my experience, "AT" type SMPS have a fairly good regulation circuit. I've never seen a 10% variation of the +5V rail...
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    I don't expect it to regulate that "poorly". With...

    I don't expect it to regulate that "poorly". With about 10mA load, its output voltage is 5.5V, with 160mA load, it's 5.2V, with 730mA load, it goes at 5.0V.
    My question since the beginning is: is...
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