25 Jan
2011
25 Jan
'11
12:18 p.m.
Folks,
Picked up one of these wee beasts today at long last, Z80 CP/M and CP/N
machine from ~1981, complete with not-oft-spotted hi-res colour PAL boards
The H-res board is not that rare. The PAL enocder is, if you have that.
Most of them just have the composite monochrome output (which is
standard) and maybe the RGB encoder (recognisable by the 4 BNC sockets --
you cna internally configure it for sompostie sync o nthe 4th socket or
sync-on-green).
and incomplete as it's missing its floppy drive
cable but I can probably
Is this the 5.25" floppy version or the 8"? I thought the former normally
had the drives in the processor box, in which case the cabel is internal
(but you say you've not dismantled it). The floppy controller is based on
a 1771, and has a standard Shugart-ish interface for the drives.
thieve one from the BBC Micro-style Cumana dual drives
that I have in
abundance.
Alternatively, a bit of ribbon cable, some IDC connectors and a bench
vice :-)
The case, PSU and mains socket tell me it's been stored somewhere damp for a
long time though I know for the last 10 or 11 months it's been on a shelf in
an electrical retailer warehouse so clean and dry.
Capacitors in the PSU notwithstanding, what else should I check before
applying 240V? Can the PSU be powered up slowly with a variac? I don't know
if it's a switcher or not but it's big enough not to be! Initial dismantling
hasn't happened yet...
You get inside from the top (the top plate of the cabinet is held on by
screws at the abck. The PCBs stad vertiallyt in card guides and are
interconnected by a 50 way ribbon cable along the top. There is no PCB
backplane/motehrboard. Other cables plug into these boards too, going to
the flppy drives and the rear panel connectotrs. The text video board
connects to the CPU board by a special cable (soldered to the video board)
The PSU output to all the cards is carried by a tiny 10 way ribbon cable
and connecotr that plugs into the CPU board. Power between the PCBs is
carried along the bus ribbon cable. I don't like it!
IIRC there are separate output cables from the PSU to the disk drives.
Iwould start by making a diagram of waht goes where, then disconnecting
the ribbon cables and taking out all the PCBs (there are a few cables,
particularly coaxial video ones that you can only disconnect when the PCB
is out, so be careful.
It's been a logn time since I've been insde the PSU of one of these
machines, but I seem to rememebr a metal chssis over it carrying the
regualtors, etc. It comes out fairly easilu revealing the mains
transformer. It's a linear PSU (or at least that origianl was, I guess it
could ahve been modified over the years).
The original PSU does not need a dummy load.
Waht I would do, due to the possible dampness problems, is to check the
earth continuity and the insulation resistance (the latter with a megger,
preferably 1000V) Assuming it all checks out, apply mains and check the
PSU output voltages. Then set up the minimal system (CPU + text video
boards, linked to a composite monitor ans see if you can ge the COS
prompt (COS == Cassette Operating System, of course). Then assemble the
complte machine nnd try to boot it
I don't see why the PSU capacitors should be especially suspect. But then
I don't subscribe to this witch-hunt against electrolyticss
-tony