I think the 1802 is fine, I think the RAM is probably fine too (6116s have always appeared to be very reliable, rearranging them on the PCB doens't change the fault). What I normally do with something like this is to disconnect the battery and conenct a bench supply set to the same nominal voltage as the battery (e.g. 4.8V for a 4 NiCd pack) in place of it. I ahve no idea what the adapter for the original microwriter was (is this the one with the VF display?). Mine is a later model with an LCD display, it has 4 NiCd cells in series inside and a very simple (diode + resistor) charger circuit. I would guess the adapter was a nominal 6V thing, rather more off-load. -tony

On Tuesday 03 January 2006 12:34 am, Steven Canning wrote: I wonder if that's why they were so fond of calling their CMOS "COS/MOS"...? -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin

Thanks, no I'd not spotted that. Tomorrow (it's getting late...) I will see (a) which states it is going into and (b) if the pulse on SC1 occurs coincident with TPA. And so on. -tony

No, CLEAR and WAIT are both high. However, I did some more testing this afternoon. The SC1 = 1 pulse occurs during TPA and SC0 is low at that time. The thing is duing an interrupt acknowledge cycle. And a bit more trsting showed that there were pulses on the INT/ input, not going low enough to be dectected as a sloid low by my logic analyser, but low enough to trigger the 1802. And those came from an RC circuit that's working correctly. The idea is to generate an interrupt about 0.1s after the last one, thus giving some kind of heartbeat clock. This is doing the right thing. After doing some more tests, I have come to the following conclusions : 1) The CPU is working fine 2) All the small glue logic chips are fine 3) The CPU is executing instructions from ROM, cna read/write RAM, etc So my current theories as to the likely fault are either bit-rot in the EPROM (but a dump of it looks reasoanbly sane, there is readable text for the setup messages, etc, so it's not totally dead) or garbage in the RAM that needs to be initialised out. In either case I need to find somebody who has one of these machines (It's a Microwriter MW4/10). The ROM is socketed, but it's a 2564 which has rahter different pinout to a 2764, and some programmers can't handle it. Mine can, and I even have a few blanks in the junk box. But my first though is that it's just an initialisation problem. I do need to find a user manual... -tony