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tomlee59

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  1. tomlee59

    Mac Plus screen adjustment

    If you look carefully, you will see that both vertical and horizontal dimensions are affected, not just horizontal, and only slightly (10% is not a huge variation). That's an important clue. Your problem may be no more complex than the yoke not being mounted flush against the crt. Take a careful look at it and remount if necessary. If the yoke is mounted fine, then your only remaining option may be the geometry adjustment magnets arrayed around the yoke. I recommend first noting their positions before randomly rotating them, otherwise you may end up making things worse than they started.
  2. tomlee59

    Mac Plus screen adjustment

    Reversing the polarity on L3 cannot have any effect if C1 is truly healthy, since the job of C1 is to block dc. If there's no dc, then L3 behaves the same regardless of which way it's inserted. Since you replaced C1 with a high-voltage cap, I'm inclined to absolve the capacitor of any role in producing nonlinearity, but that also makes me doubt that anything changed at all when you reversed the connections on L3. It's hard to tell from a nearly blank display field whether anything changes, and by how much. You might want to put up a page of text filled with characters. I wonder how much of what you think you see is actually there. You will want to know if the linearity gradually shifts in going from left to right, or if there is a more abrupt change (i.e., linearity is good within both halves, but the two halves don't match). Details like that are useful clues as to what could be wrong. Putting magnets on L3 will certainly have an effect, as you've noticed, but that's not a cure. You need to find what's causing the nonlinearity in the first place. And the first step before that is to characterize it more carefully so that you can quantify any fixes that you implement. Standard things to try first include touching up all the solder joints on J1, the flyback transformer, and components associated with those. Check CR1 and CR5 and their connections. Resistances in all of those connections can cause nonlinearity. There's also a cap from flyback pin 4 to +12V; check it, too [pin numbers are from my Compact Mac Repair doc; I don't think there are any numbers silkscreened on the PC board]. In other words, check those obvious things first before applying band-aids.
  3. tomlee59

    Lost Mac Plus keyboard cord

    Yes, exactly. It's so easy to do it right that there isn't any justification for trying the wrong way just to see what happens. Applying power backwards to semiconductors rarely results in a happy outcome...
  4. tomlee59

    Lost Mac Plus keyboard cord

    Note that Dan is a digital engineer. He has clearly not run many (or any) experiments, and is just voicing an opinion. He would not get a good grade in my circuits classes. His answer about the "heavier gauge wire" is utter nonsense. The currents flowing (both signal and power) are so small that any voltage drops would be completely negligible. The real reason for the incompatible cable is simply that Apple has traditionally wanted to force users to buy Apple widgets. In contrast with Dan, I'm an expert in the sense that I have learned from the vast number of mistakes I have made, or have seen others make, whence wisdom and scar tissue derives. When you use an ordinary telephone cable in place of the correct keyboard cable you are applying power to the keyboard in REVERSE POLARITY. You are not simply "grounding 5V". Although doing so doesn't guarantee keyboard destruction, it certainly makes it likely. You are relying on the Mac's power supply limiting the current to a value below that which would destroy the keyboard electronics. That's an unsafe bet, as the current limit is set to protect the power supply, not devices connected to it. As to your static electricity hypothesis, note that the impedance levels are much reduced on the keyboard when reverse polarized. If static electricity were strong enough to destroy the keyboard in that condition, then you would see a great many failures from static electricity when using normal cables. It ain't static. It's reverse polarity. No more experiments needed, and no appeals to Kottke's ill-founded opinions will change that.
  5. tomlee59

    Lost Mac Plus keyboard cord

    No, not static electricity. As techknight says, you were lucky, plain and simple. You shouldn't assume that everyone else would be as lucky as you.
  6. tomlee59

    Macintosh Plus Chirping Noise

    That's also a first for me. Thanks for the pic. I'll have to open a few units and see how common this is/was.
  7. tomlee59

    Low 5V line from (recapped) SE Power Supply

    If the logic board is drawing enough excess current to pull the 5V line low, something on it should be getting decently warm. With care, you should be able to find it. The area between your upper lip and nose is particularly sensitive, so if you don't own a thermal imager, that's not a bad substitute.
  8. tomlee59

    Macintosh crt related deaths

    There's all kinds of misinformation and downright nonsense in some of the posts here. Current through the heart is indeed an important consideration. But comments like "It takes X volts at Y amperes to kill you" make no sense at all. Current and voltage are related by Ohm's law -- your body is a resistor, so if you apply X volts, the current will be automatically determined by your resistance. You simply cannot specify both current and voltage independently. The charge stored in a 9" crt is far too small to do you in. Yeah, it can hurt like hell, but fearing it as a life-threatening event is overdoing it. And unless you specifically need to disconnect the crt, there is no need to discharge it prior to working on the mac. There are no exposed terminals with high voltage on them, so just leave it be. If you do need to discharge the crt, clip one lead onto the metal band around the crt first, and then connect the other lead to a screwdriver (or something similar) and slide it gently under the anode cap (the suction-cup like thing on the bell of the crt; see the Classic Mac repair guide for pics). That will take care of it. Connecting one end to a cold water pipe is not guaranteed to work, and is unnecessary in any case. All you want to do is to short out the capacitor, and that means providing a conductive path between its two terminals. No need to take the long way around! And the cold water pipe wouldn't work if the Mac isn't plugged into the wall (and you shouldn't be working on it with the thing plugged in). Don't be confused by the word "ground" or "earth". Even airplanes have "earthed" connections, but they don't achieve this by dragging a 5-mile long wire behind them.
  9. tomlee59

    Crackle and tons of nasty SMOKE! Mac 512Ke).

    I second that recommendation. Poly over paper. Always.
  10. tomlee59

    Mac Video Adapter

    I know the author quite well, and he proudly admits to laziness.
  11. tomlee59

    Mac Video Adapter

    The Classic Mac Repair Guide has a verbal description of how to put one together. Sorry that it doesn't have a schematic -- the author was a very lazy fellow.
  12. tomlee59

    Mac Video Adapter

    The output can also drive some modern monitors (not all can handle the low resolution, but many can). I homebrewed an equivalent interface module back in the day, to drive a large monitor. You haven't lived until you've seen System 6.0.8 on a 21" CRT!
  13. tomlee59

    Help with two Mac issues

    You might find the Compact Mac Repair Guide of some use in debugging your classic. It's among the Stickies, above.
  14. tomlee59

    Macintosh Plus boot problem - Maybe a cracked solder?

    Don't forget J1. It causes trouble more often than the flyback joints. Check C1 while you're at it. (And again, for details see the compact mac repair guide among the stickies.)
  15. tomlee59

    Macintosh Plus boot problem - Maybe a cracked solder?

    There are several joints that frequently cause trouble in the classic Macs. See the repair guide among the stickies for details. Good luck!
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