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AlexTheCat123

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  1. AlexTheCat123

    Apple Lisa No Video

    All of the PSU voltages seem to be fine.
  2. AlexTheCat123

    Apple Lisa No Video

    I checked/reseated the connectors and they seem to be making contact just fine. What should I try next? I'm guessing the problem has something to do with the lack of the 300V and -100V voltages or the 5V bus that is too low.
  3. AlexTheCat123

    Apple Lisa No Video

    I have replaced all of the capacitors as well as the TDA1170 chip and nothing changed. I'll check the connectors right now to make sure that they're making contact. Do you have any tips on getting a multimeter probe down on the bottom part of the video board? It's really hard since there's a CRT in the way.
  4. AlexTheCat123

    Apple Lisa No Video

    I have an Apple Lisa 2/5 that was working fine up until about a month ago. The screen started randomly collapsing to a horizontal line and eventually got to the point where it was unusable because it was a horizontal line all of the time. After a few weeks of troubleshooting, I found that the problem was a bad trace on the CPU board that made the vertical sync signal intermittent, but after fixing this trace, the screen now displays nothing at all. The heater in the neck of the tube is glowing, but there is nothing on the screen. When measuring voltages on the video board, I discovered that the 5 volt line is actually around 2.7-3.7 volts depending on when I measure it. I also noticed that the power supply lines that are supposed to be receiving 100 and 300 volts from the video board for the brightness and focus pots are receiving zero volts. I looked on the video board schematic and it looks like these voltages come from the flyback transformer, but I don't know enough about the flyback and how it works to be sure of this. Could this mean that I have a bad flyback or bad circuitry that drives it? Any help would be greatly appreciated!
  5. AlexTheCat123

    Mystic Color Classic Repair

    I just received a Color Classic with a Performa/LC 575 logic board (https://www.ebay.com/itm/Apple-Macintosh-Color-Classic-MYSTIC-computer/233213293063?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649) and I am trying to get it running again. I tested the computer with my standard Color Classic logic board and the rest of the machine works great, with the exception of the Mystic board that it came with. Nothing happens when I try to power the computer on from the keyboard, so I pulled the 575 logic board out to investigate. I noticed that there were a few bent pins on the large connector that connects the logic board to the rest of the computer, so I straightened them back out. The only problem is that they are no longer secured to the piece of plastic in the connector and they are slightly bent up away from the piece of plastic. How should I go about securing them back to the plastic part of the connector so that they make good contact and are not bent again when I reinsert the board? Any ideas? Alex
  6. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    That is very strange. The link still works fine for me.
  7. AlexTheCat123

    Does anyone know what this symbol means?

    Thanks pcamen. That's what I was thinking, but I wanted a second opinion just to make sure.
  8. I am currently repairing a Mac Classic II that I picked up a few weeks ago and I have found a capacitor that appears to be burned on the bottom of the logic board. Of course, I need to replace the cap (C39), but the schematic for the logic board shows a weird symbol after stating the value of the capacitor. A picture of the symbol can be seen in the attachment below. The symbol looks sort of like a combination of a P and an F, so would it be correct to assume that this means picofarads? I can't seem to find any other mention of this symbol on the internet anywhere. Thanks! Alex
  9. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    Unfortunately, there is not. Five or six of the pins are broken off entirely and several of the pads on the motherboard have been completely eaten away by the corrosion.
  10. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    Really? If that is that case, then it would be really cool if someone could program a microcontroller to emulate the PRAM chip.
  11. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    Darn. I guess I won't be able to get the Quadra working after all because replacement RTC/PRAM chips seem to be pretty much impossible to find.. Thanks for all of the help!
  12. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    I am certain that the SCSI drive has a compatible OS on it because it is running System 7.5. According to my research, U92 is the RTC and PRAM chip, so that shouldn't have anything to do with the SCSI bus, right? It is a relief that the green tint is probably not a problem with the computer itself. I was sort of nervous that I had yet another repair problem on my hands.
  13. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    I tried desoldering and resoldering U92, even though it is missing some pins, and to my amazement this caused the computer to boot to the blinking floppy disk screen. It will boot just fine from floppy, but I now have two more problems. 1. The screen has a greenish tint to it. What is causing this? Is it my monitor or is it a problem with the computer? 2. The computer will not recognize or boot from a known good SCSI hard drive. At the blinking floppy disk screen, the drive's activity light flashes briefly every second or so, but the machine will not recognize the drive. What is wrong with the SCSI circuitry on the logic board?
  14. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    I have now replaced all of the parts that were missing, with the exception of C61, which I have not ordered yet, and U92, which is only hanging onto the board by only a few pins. I now get a startup chime when I turn the computer on and the reset and interrupt buttons seem to work fine. However, when I hooked the computer up to a monitor I saw that it had a sad mac error with the code 0000000F 00000001. Is this likely caused by the absence of U92 or is it something else?
  15. AlexTheCat123

    Macintosh Quadra 700 Battery Leakage

    Thank you for the pictures! I agree that it appears to say IA5. I believe this means that it is a 0.1uf capacitor.
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