Jump to content


  • Content Count

  • Joined

  • Last visited

About tomlee59

Profile Information

  • Location
    Palo Alto, California

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. 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 st
  2. 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
  3. 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. 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,
  5. 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. 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. 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. 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 ev
  9. I second that recommendation. Poly over paper. Always.
  10. I know the author quite well, and he proudly admits to laziness.
  11. 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. 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. You might find the Compact Mac Repair Guide of some use in debugging your classic. It's among the Stickies, above.
  14. 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. There are several joints that frequently cause trouble in the classic Macs. See the repair guide among the stickies for details. Good luck!
  • Create New...