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I mean, it just doesn't run if you have 24bit mode set, there are only so many hours in the day and I'd already spent over a week writing the extension and control panel. 24bit mode completely moves all the memory locations around that are being written to, there is a way to briefly switch to...

I have some of these on the side : https://github.com/GeorgeRudolf/OldMacATX I tend to just use them for bench testing though. When I don't actually just use a period PSU. Thank you for the offer though. I will have a look at the design out of interest too. One IIcx thing - it is one of the few...

Excellent news! The drive should be a 1.44MB drive, which means with a bit of creativity and software you should be able to write disks from a PC. I'm actually impressed the floppy drive works, might be worth giving it a careful clean and lubrication if you haven't already. A stiff mechanism can...

Oh, and if it isn't too late, take super care, moreso when removing SIMMs, but the catches on those SIMM slots are insanely brittle. It can help to heat them a little with a hair dryer first. But regardless, avoid moving them any more than needed, and try to apply force to more than just the...

That is a sad chime, and means the basic hardware test failed (sort of similar to a flashing floppy disk light on an Acorn). But... Given you don't have any RAM installed, I wouldn't expect anything else. So given the context, this is excellent news! Well done! You need to put four 30pin...

Was it turning off the pin detect, or did you turn off "check ID"? Or is that already off I guess? The pin detect might be failing due to it being a mask ROM - the erase pin might not be being detected as normal or something. No idea. OK, at this point, its probably best to assume your primary...

Ah sorry, I thought you'd removed them in order for some reason. Could you upload a photo of your ROMs? Might be driving harder, or the fault is still on the board - the chip might be completing a circuit that is caused by a short or something weird like that. No fault of the chip. Possibly...

They wont, remember that you're looking at quarter of 32bit words cut up, not continuous data. Remove it from the socket, clean the pins and try again, it probably just isn't reading properly, or is possibly faulty. That is the one that you suspect is bad, so that isn't a surprise. If it works...

That sounds like good news! One thing I'd check, try measuring the resistance between SEL and 5v on each of the ROM chip footprints - to check if there is something holding it high on the board. Edit : Was being stupid. Another thing is given it only worked after you removed the final ROM...

I don't think that would make sense, surely the low byte would be the low byte, regardless of if you were LSB or MSB? I think you're perhaps over thinking it. Easy to check by reading the removed chips. I wouldn't jump to any conclusions - Apple mixed chips fairly often. This is a Performa 630 :

If you have the TL866+ style (or its replacement that I forget the name of) programmer, the software it comes with supports writing ROMs like this. I found out after writing a python script to do it for a RiscPC, and then when I went to write the ROM files I'd made, I saw the option built in...

It got better :) I replaced the port and cleaned the area up. Reflowed what needed it.

Oh, also, some people sell their old apple ROMs on ebay, any SIMM from a IIx, SE/30, IIsi, IIfx and several other of that era of machines, will work in the IIcx. Sadly they're soldered in most machines, but sometimes they aren't.

Yeah, ROMs do go bad sometimes. Getting a SIMM is the best answer if you don't mind spending the money. They're a good thing to get anyway because an aftermarket SIMM has a number of advantages... They're 32bit clean, which lets you use up to 128MB of RAM without needing software patches. They...

Check the settings on both rather than just one. Termination issues are like echos in a cave, they bounce around and the issues don't always appear next to the cause. Just because one thing is fully behaving, doesn't mean they both will. Also, swap the cards over and see if the fault follows the...

By the way, did you say you had a logic probe? It might be worth wiring up some of the address bus on a ROM and seeing if you get the expected request for $0. Plus the correct enable signals. Sorry if you already tried this.

Would it help to fit a 5R or 10R resistor to the end of one of the probes? Perhaps just lift it out of the range so you only beeped for real shorts?

Macs can have such a low resistance that some meters will beep continuity between ground and 5v on a working board. It... can make trouble shooting tricky :ROFLMAO: The first board I repaired I had to get my dad to measure the resistance on his similar machine to check because I couldn't...

I get 16R at the hard disk power connector between Gnd and 5v. That is in line with what I've measured on other Macs in the past. They're very low resistance, not sure if it changes when they power on or what. I guess it is only 315mA. 10R is a bit lower, but I'm not sure what the tolerance...

I'll measure one of mine, just a mo.