DRAM 128K system has stopped working

[CheshireNoir]

You and me both, someone.
I rely on tiny post-it notes and LOTS of cross referencing what I have already posted, and even then I get things wrong...
Well, the work week is over, which means I can get the 'bee back on the bench :-)
Ewan, I have replaced C46. No change.
I'm getting some 27128 ROMs blanked so I can try some ROM images.
Interestingly I dropped back in the RAM test ROM and I'm now seeing it fail at random locations while doing the RANDOM NUMBER test, somewhat, err, randomly. Certainly at different addresses each time.
I've also been monitoring the power rails and seeing a bit of fluctuation. Nothing I'd call terrible. probably ±0.2V but it comes and goes. The voltages will be stable, then they'll flicker, then they'll go stable again.

I have a bunch of 1/2 watt TRACO 7805 replacements. I could drop them in instead of the 2 regulators on the core board, assuming the core board doesn't pull more than half a watt per regulator.

I'll update the post once I've tried a BN54 ROM and a combined BASIC ROM. (I think Ernest suggested both of those)

Cheers, and always, thanks for your help.

Chesh

Ps. If I cant get things working by the end of this week I'll pack it up for Ewan to look at. I know when I have reached my skill limits. There's also the matter of the 3 different Amigas I have recently received that also need attention :-D