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Did you make sure the crystal was oriented correctly? It worked fine for me twice.

Yes, simply replacing the crystal is enough. Even without a heatsink or fan, it should work fine. Is your crystal working properly? I got mine from Aliexpress.

My IIfx is running at 50 MHz without any problems — I use it almost every day. I added heatsinks all over the board and a tiny laptop fan on the CPU, but it doesn’t get very hot compared to stock.

If you don't get the chime, don't expect anything on the screen. The ROM is probably not being read, possibly due to a broken trace or a faulty IC.

To me UC7 is bad, you'll need to replace it.

If the RAM is bad or missing, the machine will produce the death chime. If there's no chime at all, the issue is more serious — possibly a broken trace or a faulty IC.

This part of the board drives the soft power circuit. Any broken trace is a problem. To test a trace you suspect is cut without following it to the end, you can simply scrape it slightly to expose the copper.

Broken traces around UE13 (HC132), or just a bad chip.https://oldcrap.org/wp-content/uploads/2023/04/apple-iici-schematics-startup-circuit.gif

There are some electrolytic capacitors that you should definitely replace, they're probably leaking.