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Recent content by bigmessowires

  1. bigmessowires

    Macintosh Portable, feeding 7,5V, 1A instead of 1,5A - will it work

    Hmm, if the video is correct then that's quite unusual and an example of a poor design from Apple. He's basically saying that there's no battery charging circuitry in the Portable: it just directly connects the AC adapter to the battery and relies on the fact that the adapter isn't capable of...
  2. bigmessowires

    Homebrew Mac case replacements

    A couple of years ago I designed an "orange monster" case for the Mac LC / Performa 475 computers. It was built from interlocking laser-cut acrylic panels, with a few screws. https://68kmla.org/bb/index.php?threads/homemade-mini-case-for-lc-p475-q605.7239/
  3. bigmessowires

    Macintosh Portable, feeding 7,5V, 1A instead of 1,5A - will it work

    You don't necessarily need a 7.5V 1.5A supply, you just need 7.5V and anything 1.5A or greater. The amperage rating is the maximum current that the PSU can supply, but there's no problem if the computer actually draws less than the PSU maximum.
  4. bigmessowires

    SE FDHD no power

    My first thought upon hearing this was a power switch problem. Cruddy corroded switch contacts. What happens if you try wiggling the switch, or flipping it from 0 to 1 slowly and gently?
  5. bigmessowires

    Reverse Engineering the Macintosh LC Logicboard

    It looks the the pixels are correct, but some video lines are shifted over by a few pixels? I don't think that's the DAC. It's hard to see in the photo, but are the lines always shifted by a multiple of 8 pixels? Somewhere there's a counter circuit that will be generating consecutive addresses...
  6. bigmessowires

    PEx ROM Project

    You're using HY29F800? It seems similar to other 5V Flash ROMs like the SST39SF, and the datasheet for that chip says more about what happens if /OE and /WE are both asserted. "Write Inhibit Mode: Forcing OE# low, CE# high, or WE# high will inhibit the Write operation. This prevents inadvertent...
  7. bigmessowires

    Reverse Engineering the Macintosh Plus PCB

    I'm logging in for the first time in a year, just to say that this is cool! The old ROM-inator kit was basically just a pair of parallel Flash ROMs, large enough to hold the original ROM data and with the extra space used as a ROM disk. The ROM data image was slightly modified to support the...
  8. bigmessowires

    Mac IIci PSU recap advice

    Ahh, some logic board schematics are in this collection here: The relevant part for the Mac IIsi startup circuitry is on the page with the ADB stuff: I I see D3 and R115 that Doug mentioned, at the lower-left. But I also see some crazy stuff... the 68HC05 doesn't appear to be powered by 5V...
  9. bigmessowires

    Mac IIci PSU recap advice

    I tried replacing my soft power mod with your circuit exactly: an NPN BJT with 1K pullup and 10K base resistor. The startup from soft power works reliably, but it won't turn off. Here's what I observe on the /PFW signal from the logic board, when I try to shut down: The /PFW signal starts at...
  10. bigmessowires

    Mac IIci PSU recap advice

    Yes, the IIci works reliably now after adding my patch wire, using the ATX PSU and soft power mod. I spent a long time with the IIsi logic board and a scope, but I couldn't figure out exactly what's wrong with that board and why it turns itself off. However, I'm suspicious that the "soft power...
  11. bigmessowires

    Mac IIci PSU recap advice

    Thanks superjer2000, I saw some of your earlier posts and they were very helpful. My latest update: my IIci is sort of working. I decided to go one machine at a time, put aside the IIsi for the moment, and try to debug the IIci startup circuit using this schematic: This machine was recapped a...
  12. bigmessowires

    Mac IIci PSU recap advice

    Anyone have a list of caps in the IIci PSU (Astec version), or a walk-through of the process? After disassembling the PSU (a complex enough job by itself), I was surprised by the complexity inside. There are four separate PCBs and something like 30 individual caps. Many of the caps are...
  13. bigmessowires

    IIsi and IIci Power Problem Troubleshooting

    The ATX power supply works! At least on the IIsi - I haven't tried the Iici yet. The only problem is that the IIsi audio doesn't work, but I don't think that's related to the power supply. As I recall, the IIsi speaker contacts are prone to corrosion. What I did was get an 8-inch ATX extension...
  14. bigmessowires

    IIsi and IIci Power Problem Troubleshooting

    My IIsi and IIci are both having trouble booting, with the same symptoms. Both systems worked when I put them in storage about 2 years ago. Both logic boards have been recapped. The IIsi power supply was also partly recapped. I don't remember about the IIci power supply. When the power button...
  15. bigmessowires

    Need Testing Help with Mac External 400K/800K Drive

    If you have a multimeter and a Macintosh External 400K or 800K floppy drive (models M0130 or M0131), I could use your help with a quick test. Put your meter in continuity check mode (where it beeps if there's a short circuit), and test for continuity between pin 9 of the drive's connector and...