Grundy NewBrain: Part 2 (Pulling it apart)
11PSU is fixed but the NewBrain still ain't working (blank white screen). It did briefly work when I first powered it on, but nothing since.
It has two banks of RAM - if the lower bank has a failure then it won't boot so I tested that first. This can be done by grounding the RMSL (assuming "RAM select"?) line ... shorting the expansion port pin 1 to pin 6.
No change.
So pulled it apart to have a look. Quite a densely packed machine. I removed the UHF modulator can as it wouldn't be used.
Will need to do some more research into what the various parts are. I have spotted the ROMs although not sure how they work just yet:
406: Mostek MK37052N-5 (custom 8KB ROM)
407: unpopulated
408: NEC D23128C (16KB PROM)
409: Mostek MK3880N-4IRL (Z80 CPU)
There is no documentation about the MK37052 because it's a custom MK37000, where the 052 indicates it's for Grundy (I presume).
This gives the NewBrain 24KB of ROM which seems to match the documentation, three 8KB blocks:
A000 to BFFF: OS & graphics routines
C000 to DFFF: BASIC
E000 to FFFF: I/O system & maths routines