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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.

I think we have wires crossed, that's what I was saying. I was using it as evidence that code isn't executing because it never goes low from its reset state of high.

I'm pretty sure that the overlay starts high : ...

Just double checked, you should have three jumpers fitted on the board total. W1, which enabled the onboard ROM, and W3 with two jumpers, which are always fitted - they're something to do with disabling some CPU lines that were probably used during debugging at Apple.

Good work, it is that hard bit. Tedious and repetitive. Yeah, that sounds like no code is executing. If I have things the right way about, High is the start state, and it should drop low when code starts executing. Hum, given the above, we already half have an answer, but what I'd probably do...

Lets take a pause and breath in how awesome it is that someone cloned a Rocket before we ask them to do an even more difficult job of redesigning it into something even the original manufacturer didn't make :ROFLMAO:. Also, apparently modern FPGAs often struggle to get the low latency...