Hi !

> If I remember rightly I've got to move that little switch on the back part
> of the machine to down position and then connect a serial terminal to the
> printer port. But every combination of switches and serial and printer
> ports gave no output on my terminal (BTW, thats minicom 1.81 for now).

Correct settings are: switch (S3 i think) UP, console at the printer port.
There should really get out something. Minicom should work, used it here also
a long time. Try to disable all handshake (XON/XOFF and RTS/DTR), serial
settings are 9600-8N1.

> Are those red LEDs on the back a help for diagnostics? I've already
> removed the 8-plane card. What next?

The SCSI adapter is the only removable part. You could try to push all chips on
sockets in. Maybe an EPROM or so has loosened with the transport. Just give
them much force, maybe some get 1-2 mm deeper to the socket.
The LEDs may really be useful, they do a similar countdown as the console
display does. I don't have the codes displayed, maybe the high nibble is the
number given on the console, but don't know. If they don't change, you may
have no system clock or the EPROMs have no contact or are defective.
If they change, just watch them, als try to find out, at which value it hangs.

so long.. Michael