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That’s the thing, I don’t think it’s a GAL. GALs aren’t in-system programmable and they stop working during the programming process. It seems like some kind of ASIC.

The Brainstorm is super interesting and I have never encountered an explanation of exactly what the bus interface chip does. You'd think it would be simple but it's not... the bus interface IC can evidently be reprogrammed by software on the Mac (!). Indeed there is an update for earlier...

Unfortunately the current hardware doesn't really support that. When the Mac writes to the card, a few address bits are latched as well so the ESP32 can see what location was written to and there can be multiple write streams to the card. But when the Mac reads data, there aren't multiple...

At the very least, the -12V goes to power the -5V regulator and to the NuBus slots. I think the -5V regulator is what Steve was referring to when he was talking about a part taking in 12V and making 5V. That must be for the negative supply. The main positive 5V supply is too high current to make...

I've had to add another little subsystem to my design: In the top right is the new USB update functionality. My implementation is fairly expensive ($4-5) but I think it's a necessity for users to be able to update the card without special hardware. The MCU in the QFN package is actually an...

You mentioned a short in the power. What's the voltage on the +5V rail when the 840AV is on? Also check that with the machine on, the /RESET pin is high (above 2.0V). If not then the system is not coming out of reset and you should check the power-on reset IC as @Elemenoh said. Have an...

I'm trying to add the onboard Ethernet to my Centris 610 which didn't originally have it. In order to do this, I have to burn the 82S123 32-byte “Ethernet ID ROM” that contains the machine's MAC address. Can anyone who has a Centris with Ethernet post the contents of their Ethernet ROM so I can...

Just a pain in the ass for hooking up the logic analyzer and scope, plus I plan on making 100+ of these so I have to do production testing.

Hmmm well the WaveJSON-to-verilog approach for generating the test vectors was not really successful, long story short. I'm just gonna do another set of test vectors for verification purposes. Also I need to get an SE board mounted on a board of wood with a PSU, disk, and some kind of video...

The basic framework for the Mac driver is coming along nicely. I have a rudimentary WiFi control panel which also houses the requisite DRVRs and the INIT to install them: I can upload source if anyone is interested but I've been developing on my Quadra 660AV (lovely machine to work on) so it's...

Aha! Interesting stuff here regarding initialization of the CIVIC video chip: https://github.com/elliotnunn/mac-rom/tree/master/DeclData/DeclVideo/Civic/CivicPrimaryInit.a On line 569, the CIVIC init code in ROM checks the previously-stored machine ID and sets the VRAM speed and refresh rate...

Yep!

Nothing required to do the RAM mod, just a problem on my IIsi. The connection between D4 of the ‘030 data bus and the RAM bank A data buffers was broken so I had to run a wire.

Currently Garrett is assembling the VRAM stacks which we are going to swap onto the board. Here’s some pics Bending out the leads: Stacked atop unmodified SOJ: Separating the RAS and SE: Soldered: All credit for stacking these things so meticulously goes to my best friend Garrett Fellers...

Woohoo! Found the problem and put a bodge wire, now the system works and shows 4 MB of RAM! Gonna remove the crappy bodge, put 74F245 buffers to make it more “authentic” than these AHCT parts I threw on, clean the board, then Garrett is gonna put a neater wire taped down to the board with kapton.

The ROM is the same but it does have to program the VRAM wait states differently for the 660AV and 840AV, so it’s possible that the extra VRAM would not be enabled on the 660AV. I’ll see.

I have been burned by “popcorning” both in my repair work and also in small production runs too many times and now I almost always desiccate populated boards and parts at 80-100 Celsius for 24-48 hours before hot air rework or reflow soldering. Does anyone else do this? In my experience, the...

Alright, 660AV has been recapped and I think it’s working perfectly. It was missing a SCSI termination voltage regulator somehow so I borrowed one from another board. Once I test a bit I’m gonna assemble the double VRAM stacks and replace em. I’m using 70ns VRAM in since I have it on hand and...

Replaced the four ‘ALS245s and still death chimes. I’ll have to go through everything related to the RAM bank A with a multimeter to check for continuity

Put the 1Mx4 DRAM chips on, still death chimes. Damn! I was hoping it’d work. Now I don’t know whether the 4 MB VRAM array doesn’t work or whether the board is bad in some other way. 68k bus must be working since otherwise it couldn't death chime. The interesting thing is that after I removed...