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Type: Posts; User: Dwight Elvey

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  1. If aluminum oxide, it is really abrasive. If it...

    If aluminum oxide, it is really abrasive. If it is zinc oxide, it is much less abrasive. Both materials were used in drive frames.
    Dwight
  2. I was there in the early 1970s. I'm sure things...

    I was there in the early 1970s. I'm sure things have changed since then. I orders a couple 12V CT transformers and used them as boost auto transformers. I then used a Variac to fine tune. It worked...
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    There are a lot of errors that a checksum will...

    There are a lot of errors that a checksum will not catch. It was only used because CRCs were slower if done in software. There are ways to speed it up. A good 32 bit crc is almost impossible to not...
  4. I went back and saw your note about the -18V....

    I went back and saw your note about the -18V. Yes, the positive side of the capacitor for -18V is connected to the ground. The negative lead is the -18V rail ( post 24 ).
    The resistor just needs to...
  5. Most people are not that thorough in checking...

    Most people are not that thorough in checking every byte of the keyboard directly. Most would be happy to see the right character on the screen. One wonders how long the typos were there in the...
  6. There is a difference on the schematic not shown...

    There is a difference on the schematic not shown for 220V compared to 110V. The 220V would use a capacitor rated for about 450V while the 110V would be two capacitors of 250V as shown in the...
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    There are many CRC polynomials to choose from for...

    There are many CRC polynomials to choose from for each length of the polynomial used. One can also use the multiplicative or the divide type algorithm for each. Which polynomial used is important to...
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    Get at least a 50MHz sample rate scope if...

    Get at least a 50MHz sample rate scope if digital. There are lots of good used 100MHz analog scopes available. Do look for one with delayed sweep.
    Dwight
  9. First measure with an ohm meter. If it is not...

    First measure with an ohm meter. If it is not shorted, that is not the issue.
    If shorted, connect it to a bench supply with the current limit, starting at about 0.5 amps. Check around the board...
  10. On the drives, it is most likely corrosion from...

    On the drives, it is most likely corrosion from temperature cycling in someones garage. Remove as much of the loose stuff that you can. You don't want that stuff to fall into the disk.
    On the...
  11. Not cheap but for less than I'd thought they'd...

    Not cheap but for less than I'd thought they'd be. I assume they latch in the value of 4 bit data.
    Dwight
  12. Someone wouldn't have a pointer to a schematic...

    Someone wouldn't have a pointer to a schematic for this thing?
    Dwight
  13. I should note, using Dave's method, remember the...

    I should note, using Dave's method, remember the polarities of the capacitors. The two smaller ones are connected oppositely. One has the + to ground and the other the negative to ground. You stick...
  14. It doesn't matter which side of the capacitor the...

    It doesn't matter which side of the capacitor the resistor goes on except there are usually more wires cross connecting the ground wires. Dave's method works well but most bench supplies are not...
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    I assume your are reading the ohms scale. It...

    I assume your are reading the ohms scale. It means OVer range, not zero volts.
    Sounds like you found the problem. I assume C121 is a tantalum.
    Dwight
  16. I can never understand why people want to make...

    I can never understand why people want to make such a mess of this stuff. Gigabite is right. You most likely got a component upside down or a blob of solder where it doesn't belong.
    Dwight
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    A friend had a Halloween party we made a large...

    A friend had a Halloween party we made a large punch bowl of various citrus drinks and EverClear. It was not recognized as to what concentration we had. We had to stop several people from heading out...
  18. Those 311's would be hard to find now days but...

    Those 311's would be hard to find now days but that is really clever for minimal parts. For me, I'd most likely use an Arduino or BluePill and LCD. You are clearly a true tinkerer. It is great to...
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    We can walk you though trouble shooting the...

    We can walk you though trouble shooting the hardware.
    We'd need information on what test equipment you have?
    We don't know which machine you have. You can find some documentation at...
  20. The light bulb may protect things but are too low...

    The light bulb may protect things but are too low a resistance to protect the large electrolytic capacitors. They likely need to be reformed. If you hit them with the full voltage, even though they...
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    With the arduino you can just use regular C. You...

    With the arduino you can just use regular C. You don't need to step into any of the OO stuff. I don't use C myself so can't help you much.
    Dwight
  22. Also check the +-12v rails. Many power supplies...

    Also check the +-12v rails. Many power supplies have what I call a kick starter to get the regulation started. They then switch to the 12V to run the rails for the regulator's analog circuits. If...
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    As Al noted, the only alcohol that is ever...

    As Al noted, the only alcohol that is ever somewhat safe to drink is ethanol. All the rest will do serious damage to your body. Methanol will often make you blind if you live through it. Ethanol is...
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    We have stuff called EverClear. You can't buy it...

    We have stuff called EverClear. You can't buy it in every state ( at least not in California ). It is so high in alcohol that if you drink it straight from the bottle it will damage the tissue in...
  25. Almost every single part on the board is require...

    Almost every single part on the board is require to work properly to have the board run. The exception is that they will almost always run with many of the rail bypass capacitors removes. In other...
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