What parts can I salvage from an Issue 2 and Issue 4B boards to populate an Issue 3B board?

[SmonkyKingus]

To cut an extremely long story short, I had two fully-functioning spectrum computers, messed them up and now I'm going to try my best to resurrect them... by sticking their parts into a whole new board. Kinda like a ship of Theseus experiment, except not in philosophy. The goal here is to use what I've got. And I've got the two dead boards, CPU and RAM replacements from Lotharek's Lair (which from my understanding means I don't need any RAM chips) and other random bits lying around.

From what I've seen, the Issue 4B and 3B boards are similar enough that I could just transplant all the (presumably) functional parts from the Issue 3B right into the 4B. Is that correct?

Could I get away with using the older ULA and ROM from the issue 2 board? I don't think I can get much else out of said Issue 2 board.

I suppose a whole list of parts would be really helpful, so I could compare. I've already found this for the Issue 4B and this for the Issue 3B... am I correct in assuming I should be able to lift most parts from the Issue 4B board and put them in the Issue 3B board?

[zx64]

You can use ULA from 4B board in 3B board I believe. But not ULA from issue 2 board.

All ROM and CPU are the same so you can reuse them as well.

[1024MAK]

Later ULAs can be used in earlier issue boards. Not necessarily the other way round. If the issue two board has its original ULA, this may not work in an issue 4A or later board (see here). Sinclair made some timing changes. There were other changes between the ULAs used for the issue two boards and issue 3 and 3B boards. It very much depends on which ULA revision it is.

The ROM, the Z80, in fact, all of the DRAM, 74LSxxx logic chips and the LM1889 can be used in issue 3 to issue 4S boards. The transistors can also be used. Not really worthwhile reusing the smaller parts (capacitors, resistors, diodes etc).

Have you really made such a mess of the issue two and issue 4B boards that nether can be repaired? The 4B has some improvements over earlier boards.

Mark