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  1. gkmaia

    Mac Plus screen issue

    Yes me too. I am reluctant to go and buy a logic board without covering all possible issues with the analog board. All books mention about replacing U2 but none mention which gate of U2 controls the horizontal signal. If I knew that I could trace all between U2 and CRT and see if I find something.
  2. gkmaia

    Mac Plus screen issue

    Just found it!
  3. gkmaia

    Mac Plus screen issue

    I know what could be then... I am reading the Mac Plus logic is grounded to chassis and I discharged the CRT to chassis without a resistor. Apparently the logic board is sensible to that. Makes no sense to be the analog as I replaced the ICs and tested all transistors. Are you able to show me which one on the board the LAG chip? Or just its marking will be enough.
  4. gkmaia

    Mac Plus screen issue

    No silly question. Any comment is welcome. That is a tricky one. Wish I had schematics with voltages and waveforms to test against. If the brightness you refer if the one in the front under the screen. It works as intended as brightness control. But messing with it does not remove the horizontal lines.
  5. gkmaia

    Mac Plus screen issue

    Could be but I have redone all the joints on the analog board. Fluxed and added a bit of new solder. Unlikely it is that. I will check continuity on all cables and see if I find anything.
  6. gkmaia

    Mac Plus screen issue

    Did some more extensive checks. Replaced the LS38. Checked most of the transistors around the LS38 and nothing. Still the same issue. Also re-soldered the large connector on the logic board just to make sure. Nothing. Any ideas?! Other things to try?
  7. gkmaia

    Mac Plus screen issue

    I just replaced the LS38 logic and nothing. Still the same issue. will try page 169 as may be a transistor.... keep you posted!
  8. gkmaia


    Hi I bought one of these and can really get it to read or format a 720k/800k disk on my mac. I am running mac os Mojave. Is there anything I am doing wrong? Cheers, Gui
  9. gkmaia

    Mac Plus screen issue

    Thanks mate! I was trying to figure out what was this DMS thing... thanks for the tip. Amazing book! It is pretty much it. I did test the 7438 and all gates seem fine. I ordered a new one anyway. Lets see if that is it.
  10. gkmaia

    Mac Plus screen issue

    I am struggling a bit to identify this fault. The computer beeps once and reads the system disk apparently fine but the only image I get is the attached one. See image attached. Following the manual I found here on the forum seems my voltages seem ok. I did read on a post yesterday (https://68kmla.org/forums/index.php?/topic/23533-plus-with-horizontal-sweep-lines/) that my issue could be caused by a fault on 7438. But it seems to be fine. So far seems the power block of the analog board is working fine. But the sweep block is not rendering the image. I could be wrong... Anyone had a similar issue? And some advise on how to approach it? J4 1 - 0v 2 - x 3 - square wave 4 - 0v 5 - 4.7v 6 - 5v 7 - 0v 8 - -12v 9 - 0v 10 - +12v 11 - 4.6v U3 4 - 330v - 20ms square wave LM 4 - 12v 11 - -12v
  11. gkmaia

    Plus with Horizontal Sweep Lines?

    Hi, I got the same issue on my Plus. Would you be able to let me know what is the DMS you are looking at? Or where I could download it? Cheers!