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Type: Posts; User: Dwight Elvey

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  1. Replies
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    Using an orange pencil eraser is something like a...

    Using an orange pencil eraser is something like a drug addiction. The more you use it the more you need to use it. First, they are made with rubber. To make rubber what it is, they add sulfur. Every...
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    I did a talk on my board at the "Virtual Vintage...

    I did a talk on my board at the "Virtual Vintage Computer West 2020". It is currently up on youtube. Just do a search for the quoted text. My talk starts at 2:54:37 and ends at 3:14:15. It was...
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    It wouldn't need more than you'd need for UPS....

    It wouldn't need more than you'd need for UPS.
    Dwight
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    I've not see such, that I remember, on a VOM. It...

    I've not see such, that I remember, on a VOM. It is much easier to just get a capacitor. They are not all to uncommon. I'd send you one but it isn't worth the postage.
    Dwight
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    For things like FluxEngine or Geaseleweazle, you...

    For things like FluxEngine or Geaseleweazle, you don't need to know the density but if you expect to use a computer with a controller, you need to know if it is FM or MFM as well. Not all newer...
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    Many VOMs are even worse. They just rectify the...

    Many VOMs are even worse. They just rectify the voltage with a bridge using copper oxide diodes. You connect 5 volts DC to a VOM and you are likely to read about 3 or 4 volts on an AC scale. As for...
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    How did you check that? Dwight

    How did you check that?
    Dwight
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    I would check the AC reading with a capacitor to...

    I would check the AC reading with a capacitor to isolate the DC path. Not all meters will read AC properly with a DC bias. A 1 or .1uf should be enough isolation for an AC reading with a typical DVM...
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    I would think it has unpredictable action. It is...

    I would think it has unpredictable action. It is possible that the intent was to make it come up in the local mode but without removing the connection to pin 1, I doubt it would be too reliable. I'd...
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    You are not likely to get far without a scope. (...

    You are not likely to get far without a scope. ( don't buy a cheap 1MHz scope. it is not fast enough to deal with the video circuit ). There is a schematic on the web.
    Dwight
  11. I still use Forth for all of my hobby project....

    I still use Forth for all of my hobby project. When I program, I make lots of mistakes. I've never found a language that I can produce working, debugged, code in such a short amount of time ( my time...
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    I should note that piggybacking is not a 100%...

    I should note that piggybacking is not a 100% valid test. A RAM could still fail in such a way that piggybacking doesn't work. It would be best to pull the RAMs and install sockets.
    Still, this...
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    First picture, upper left, as two columns of...

    First picture, upper left, as two columns of 2102s. These are generic parts so manufacture is not too important.
    Dwight
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    They use a 5V to 3.3v converter. 16 of the I/Os...

    They use a 5V to 3.3v converter. 16 of the I/Os are 5V tolerant ( at least for the BluePill ). For input TTL or CMOS is fine. For outputs it is recommended to use them as open drain and a pullup...
  15. It is a cheap way but I think the controller is...

    It is a cheap way but I think the controller is more likely at fault or tired ERPOMs. Still, it is worth a first try with no test gear. I was looking and the controllers are available on ebay for...
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    First, don't use cheap AVR chips use cheap Arm...

    First, don't use cheap AVR chips use cheap Arm chips. They can generate signals on pins from timers at rates of faster edges than 50MHz. They can trigger interrupts or timer inputs as similar rate....
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    I don't see any specifications about timing...

    I don't see any specifications about timing margins. Does it state where static RAM begins to fail, using different edges? Does it report where DRAM begins to have issues with refresh. Testing RAM is...
  18. I'm not giving it a high likelihood of fixing it....

    I'm not giving it a high likelihood of fixing it. I'd say about 20-30% chance. Jameco has these at 79 cents. If you do well at soldering and don't damage the board, without a scope or other test...
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    Many of the parts used in the VB are no longer...

    Many of the parts used in the VB are no longer available. Still the most likely failure item is the RAM. These are generally available. The most common technique is to piggy back the RAM on the...
  20. I usually order from Jameco or Anchor...

    I usually order from Jameco or Anchor Electronics. Just don't get a surface mount.
    It looks like they could be equally at fault. Used socket to put them on with. What soldering skills do you have?...
  21. First, I should note, there is only one video...

    First, I should note, there is only one video RAM, U607.
    The other RAMs are the system RAMs.
    The ROM and column counter part looks to be working right as you can see valid characters on part of the...
  22. This is different than I described. The...

    This is different than I described. The horizontal, row and veritcal video counter is built into CRT 5037.
    The part you see that has been unsoldered is the video ROM, CRT 8002-005. This part looks...
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    It is usually not the heads that are the first to...

    It is usually not the heads that are the first to cause problems on the iron engines, it is the rear seal melts. It can't usually be replaced without pulling the transmission.
    Dwight
  24. I doubt the CPU is the issue. There will normally...

    I doubt the CPU is the issue. There will normally be some counter chips that generate the sweep addresses for the video RAM. There will also be a way to mutiplex that counter with the CPU address...
  25. It is not likely the RAM. It is more likely the...

    It is not likely the RAM. It is more likely the address generation that sweeps through the RAM to display the data.
    Being static, it would be more difficult for the RAM to do this.
    Dwight

    Dwight
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