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apm

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  1. At 1MΩ there won't be any significant power flowing through the pot. On the SE/30 at least, the voltage that drives the brightness circuit is measured at 106V (according to BOMARC). If the whole voltage was applied across the pot you'd have about 10mW of power, but as the circuit is designed, the pot doesn't even see all of that. So just look for something with the right shaft and pin spacing.
  2. It depends on the resolution. If it's at least VGA resolution (which it certainly is) and not a portrait display resolution, then you should be able to hook up a standard monitor. If the output is 1-bit TTL, you can make a simple resistor ladder divider to get down to the right level and impedance. If it's a portrait display card, it'll look quite bad on an ordinary display. There usually isn't any easy way to set the width of the picture as narrow as it would need to be.
  3. Funny, just saw a similar card (for SE) in another thread. I bet the sanded-off chip is an XC2018 CPLD, which was used in loads of 1-bit video cards, like this one that @stepleton and I reverse-engineered: https://github.com/apmcpherson/VideoMacPacHack Do you have the ability to dump the ROM? I'd be curious about its contents.
  4. It uses the same CPLD as a video card for the Portable which @stepleton and I reverse engineered: https://github.com/apmcpherson/VideoMacPacHack We found the 57.2832MHz oscillator was used to produce a resolution for the Apple Portrait Display (or a full-page display by Sunkyung, according to the control panel). So maybe it would drive an Apple display, but only in 1-bit monochrome since it's an SE. No idea whether the overall design is close enough to the card on the Portable (I doubt it), but you could try the VideoMacPac software at the link above. Or look for anythi
  5. Finally, over 5 years after I started this thread, here we are: VGA 640x480 in grayscale on a Classic CRT! The above image is displayed with an original CRT and an original (modified) analog board, with a replica Xceed CRT neck board for grayscale. The display is coming from an LC II but could be any VGA source. A synopsis for those just joining this thread: the goal is to increase the resolution of the compact Mac screen from 512x342 to 640x480 (or higher). There have been several nice hacks of the display before, but they usually involve replacing the CRT
  6. It's probably a TTL video card. With a scope, you could figure out the pinout of the connector and the scan frequencies. The design probably has a lot of similarities to this Portable video card that @stepleton and I reverse engineered: Building an adapter from TTL to VGA is doable. It just involves some resistors and optionally a voltage regulator (which will clean up noise or brightness changes if the +5V line varies). There's a design for the Portable card on the GitHub repo: https://github.com/apmcpherson/VideoMacPacHack. You'd have to work out the pinouts with a scope. Also, if it's
  7. Update: I think the problem has something to do with the CPUCLK signal (i.e. the 16MHz one from the logic board), not the 50MHz clock. Specifically, I suspect the problem is clock skew from the propagation delay on the 74ACT86 XOR gate on the adapter. When I take this IC out of circuit and bypass both relevant signals (to the P33; to the passthrough) with 10 ohm resistors, the P33 seems to remain stable with the Radius card plugged in. The Radius card doesn't seem to be working at the moment, even by itself, so that needs more investigation. Looking at some datasheets,
  8. Finally got a chance to add the resistors to R24 and R26 and the bridge across C1. There seems to be some improvement: the card no longer goes unstable after it heats up, provided there's no Radius card installed. However, the Radius Color Pivot card still doesn't work, and if the Radius card is installed, the accelerator goes unstable when it heats up, like before. I can run the Mac for a long time with no Radius card with no problems, then attach the Radius card (P33 still warm) and the stability problems immediately resurface. So it is the P33 heating up that makes the differenc
  9. Progress: adding the pull-up to /CFLUSH has fixed the crash-on-cache issue. I can now boot with cache enabled and open the control panel. I can also display address $5207 0000 now. However the other issues remain unresolved: the card still goes unstable and crashes after it heats up for a while, and the Radius card still works intermittently, if at all. I'll try the clock modification next. Happy to send the card to you for testing and documentation, or let me know if you have other suggestions.
  10. Thanks, I'll try that. I do have a scope so I can probe any signals you think would be relevant. I could look at the 50MHz clock but I'm not sure I'd get much out of that: my scope only has 70MHz BW, and I'm not confident the waveform wouldn't be affected by the capacitance of the probe. However I might go sleuthing for a pin that toggles on the access to $5207 0000. Which GAL is responding to the specific accesses to $5205 0000, $5206 0000 and $520F000? I'd be happy to send you my P33 for inspection and disassembly. I think James's one is in regular service though, so
  11. All very interesting, thanks. I've tried removing jumpers C17 and B23. Now the floppy drive works with the bad P33 (hooray), and there is a modest improvement in the Radius card. Occasionally it will flicker the default grey screen with Radius logo briefly on startup, and more occasionally it will keep working as the system loads. Sometimes it still doesn't work. However, the other issues haven't changed. Accessing address $5207 0000 still results in a hang (every other address of the form $520x 0000 works fine). And the same issue persists with random errors (illegal instruction,
  12. Thanks. I hope to try some of that tomorrow. In the meantime, I looked back through the Power Central and Power Demo code, and both of them show the following flow: A condition is tested. One branch writes $520F 0000, then $5206 0000 -- this must be the "cache off" condition. The other branch writes $5207 0000, then tests a different condition and writes either $5205 0000 or $5204 0000. I can post code listings if that's useful, but basically it appears there are two more functional addresses in the GALs ($5207 and $5204). Could this have anything to do wit
  13. I've been trying to get a Daystar P33 accelerator (50MHz 68030) working in an SE/30 with one of @Bolle's amazing adapters -- in this case the model from the early 2020, short form factor with Asante ethernet card underneath. The P33 itself is faulty in some odd ways which I'm trying to figure out. Thanks to @james_w we've been able to make comparisons between this P33 and another known-good P33, and also between my Bolle-adapter and the earlier "tall" type Bolle-adapter that James has. The SE/30 runs with the P33 inserted, but it locks solid when you try to open the Pow
  14. Tom is overly modest about his own role in this project! We actually finished the design back in 2017, but the rest of life took over and documentation seemed like an insurmountable hurdle until the current lockdown. I've tried to put sufficient materials on the Github repo so that anyone can make their own board if they can get their hands on the right parts. The hard-to-source bits are the XC2018 CPLD, the 42C4064 VRAM (in ZIP package) and the oscillator cans, though you can get away with fewer and/or different frequencies depending on which resolutions you need (see the table he
  15. Yes, both monitors worked as they would on standard MacOS.
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