Not MMU, but EMMU. This is how 130XE (ECI) boards were configured for 65XE/800XE computers.

You could also replace the MMU, with another one or a programmed GAL replacement.

These "resistors" mounted instead of EMMU are just jumpers (0 Ohm).

Try to remove EMMU and cross-wire its socket, so the computer would behave as it had only 64 kB of RAM, and if it doesn't help, try to substitute MMU with another one or a GAL replacement (in 800 XL it was a PAL chip, so GAL replacement is 100% compatible).

I prefer this test for extended RAM:
https://satantronic.com/files/8bit/tools/XRAM0220.XEX

Ok, I own any TMS4164-15NL, are they compatible with the first bank (42164-15) ? By markings, they are ok, but these chips look suspicious to me. Like they were sanded and re-engraved. Do they come from Aliexpress? I had similar glitches in my 800XL, and it was a faulty ANTIC chip (it was working c...

If you want to observe just repetitive analog signals, then time equivalent sampling is ok, but if you want to catch a glitch in a digital signal, that occurs once in a few thousands (or more) cycles, then deep memory, and high real time sampling are crucial things to have. This old HP is just "deaf...

I remember those HP scopes from school, but for today's standards 54602B really isn't impressive. It is only 20 MSa/s, and for most time is working in time equivalent sampling. Its effective bandwidth for real time sampling is about 5 MHz, and has almost no memory (just 4 kPts). The entry level mode...

Graphics seem to be correct - within the EU, it is the seller (you) who pays VAT, and there are no custom fees. As for now, when you export goods from the non-EU to the EU countries, the VAT and customs fee are paid (or not) by the importer in the destination country. It is about to be changed, and ...

I've printed some of these plugs, and they fit perfectly ok.

My drawings are from "the nature", the dimensions are not super precise, especially the angles.