More on my HP7245A problem

[Tony Duell]

I've been doing some more fiddling with that HP7245A printer/plotter.

On the ROM/RAM board there are 8 9216s, arranged to give an 8K*16 program 
storage space. And also 4 off 82S123 PROMs arranged to give 64words*16, 
probably for some kind of parameter storage. Those last 4 chips are socketed.

Test 02 does appear to be the ROM test (as on the -B model). On my 
machine it seems to access all the program ROMs and the first pair of 
82S123s. It then gives up with error 54(8).

I have rpelaced the sockets (with nice turned-piu ones), no change.

By swapping the ROMs around, I think I've discovered that the test is a 
simple cheacksum, independant of the address.In particular, if I swap 
round the 2 sets of PROMs (in the test mode), it fails with error 56(8). 
And if I put them back in the right sockets, and then swap round the 2 
ROMs in the low bank, it fails with code 53(8)

This leads me to guess that the error codes (in octal) are : 

53 : U15 (PROM A MSB)
54 : U10 (PROM A LSB)
55 : U16 (PROM B MSB)
56 : U11 (PROM B LSB).

And that U10 is genuinely the problem in my machine (i.e. not the socket, 
PCB traces, or address decoder, all of which I have checked anyway).

Curiously, all 4 PROMs have the same HP part number, but I suspect that's 
the code for a blank chip, and that the contents of each chip is 
different. 

OK, it's a long shot, but does anyone have a dead 7245A that they can 
pull these ROMs from? Or any idea as to what the contents should be?

-tony