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Thread: New board: The VIC-IIČ - PAL/NTSC switch board for Commodore 64

  1. #161
    Retro YouTuber Starglider's Avatar
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    Very interesting and I like that you used my own video to illustrate that it is not caused by the VIC-IIČ

    Your theory may be correct but hopefully someone else can jump in with some ideas.
    Starglider aka Perifractic

    "Recordar es vivir" | Remembering is living

  2. #162
    rmzalbar's Avatar
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    Yes this is probably a topic for a different thread, as it has nothing to do with the VIC-IIČ which is working wonderfully. Here's a picture of what it looks like on my side:

    Click image for larger version. 

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    It's actually the issue described here (Non-fault #1 – Red/Green Bars)
    https://retrocomputerverzamelaar.nl/...e-64-problems/

    If I find a way to mitigate it, I will post it here - might be something simple enough to add to the manual.

  3. #163
    Retro YouTuber Starglider's Avatar
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    Quote Originally Posted by rmzalbar View Post
    Yes this is probably a topic for a different thread, as it has nothing to do with the VIC-IIČ which is working wonderfully. Here's a picture of what it looks like on my side:

    ...
    If I find a way to mitigate it, I will post it here - might be something simple enough to add to the manual.
    Great!
    Starglider aka Perifractic

    "Recordar es vivir" | Remembering is living

  4. #164
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    As I was assembling the VIC-IIČ tonight, I started thinking about how there are no flyback diodes across the relay coils. With 4 relays all clicking together in such close proximity on the same power supply as the sensitive VIC-II chips, is there a possibility that back EMF voltage spikes from the coils may damage the VIC-II chips over time?
    Last edited by matt64; 22nd January 2020 at 04:04.

  5. #165
    rmzalbar's Avatar
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    I'll scope it and check tonight. The relays are single-coil latching, where you reverse the polarity to switch it the other way, so the place to put the diode, if needed, would be across the two input wires from the C64 power switch.

    EDIT: Well... looking at the schematic (for 250407,) the VIC-II power supply itself is actually generated from the 9VAC input, not the 5VDC input, so it is isolated from the relay coils. Other chips do use 5VDC however. So then, looking at the 5VDC input, there is an inductor and several capacitors for input and switch filtering, so I think that is enough. I will scope it tonight to prove that.
    Last edited by rmzalbar; 25th January 2020 at 01:47.

  6. #166
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    Quote Originally Posted by rmzalbar View Post
    EDIT: Well... looking at the schematic (for 250407,) the VIC-II power supply itself is actually generated from the 9VAC input, not the 5VDC input, so it is isolated from the relay coils.
    You are correct. I've spent too much time looking at schematics of the later short boards, I forgot the VIC on the breadbin boards is powered from CAN +5V and +12V, both derived from the 9VAC circuit. It looks like the SID is powered from the same +12V but instead uses the main +5V supply though (same as the relays), plus the PLA, and RAM being the most sensitive things nearby.

    If there is ever a C64C compatible revision, everything on those boards is 5V, with the exception of a discrete 9V regulator circuit for the 8580 SID. So, something to keep in mind there.

    Curious to see what you find on the scope.

  7. #167
    rmzalbar's Avatar
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    Scoped.

    Measuring directly across +pow and -pow right on the board gives big pulses up to 100 volts, as you'd expect. However, nothing significant is reaching the 5VDC power rail, tiny bits of noise always less than 2 volts, so the C64 power filtering is handling it fine.

  8. #168
    Retro YouTuber Starglider's Avatar
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    Sorry just catching up with this. Yes, this is something we carefully considered, and I'm pleased that you came to the same reassuring conclusion
    Starglider aka Perifractic

    "Recordar es vivir" | Remembering is living

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