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apm

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  1. 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
  2. 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,
  3. 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
  4. 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.
  5. 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
  6. 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,
  7. 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
  8. 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
  9. 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
  10. Yes, both monitors worked as they would on standard MacOS.
  11. Yep absolutely. I installed that pot on the reverse side of the PCB so I could adjust it more easily. It took some back and forth between Cutoff and the PCB pot (basically, video gain) to get a good picture. Also, I discovered today that A/UX doesn't work with the greyscale harness. The screen goes black when it boots the kernel. Doesn't matter whether I started from 256 greys or B&W. However, with an external monitor attached such that the internal video goes back to the logic board, A/UX works. Anyone had any better luck?
  12. And it works! Thanks @Bolle for the PCB. Making the cable harness took longer than populating the PCB. One thing I've found is that the picture quality is quite sensitive to the Cutoff control on the analog board. In its default setting (pre-greyscale), most shades of grey were nearly black. Adjusting it improves the range of greys, but it's easy to end up with the scan lines visible.
  13. I just joined the club. I saw the following SE/30 on eBay UK. At first glance, like any other cap- or battery-damaged machine: But what caught my attention was half of a black DB-15 port, centred in the panel. Radius video cards don't look like that. Could it possibly be...? A 3.5 hour train journey out and back, and this is the result: Success! The rest of the internals are mostly a write-off. The logic board has been paid a visit by "Maxell's Silver Hammer": The hard drive ran fo
  14. I replaced the TDA4605 and recapped the whole board. Not sure if the results are progress. Now with the video cable unplugged, the monitor powers up and makes an ominous sizzly noise. I think it's coming from the flyback but I'm disinclined to get close enough to really pinpoint the source. I may have heard a couple arcs, but I can't see anything even with the lights off. There's a dim raster that overscans the CRT. With the video cable plugged into a Mac which is turned off (i.e. no signal), the sizzling stops and I get a bright white raster, wider than the screen and a bit too short
  15. Good thoughts, thanks. I think the HOT and its driver (TEA2037) are okay: there's a sensible signal at the HOT gate (not itself diagnostic), and a reasonable voltage appears on the one flyback secondary I felt comfortable to test with a 10x probe. When I retrieve my 100x probe from the office I can probe the higher-voltage parts of the horizontal circuit, but it looks like that's not the source of the problem. I will have to get my hands on an isolation transformer. Any particular reason to put the isolation transformer on the scope rather than the monitor? I guess I c
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