Recent content by apm

Nice project. Yes it should be possible to mod the Classic II A/B to get higher resolutions, and then use one of the Xceed clone CRT neck boards for greyscale. I've made a custom A/B in SE/30 form factor incorporating the Classic II flyback, which I built probably a year ago but has been sitting...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...