HP7245A ROM problems?

Tony Duell ard at p850ug1.demon.co.uk
Fri Nov 11 20:11:58 CST 2005

I am working on an HP7245A thermal printer/plotter. I have a home-made 
schematic of this unit, and have read the service manual for the -B 
version on hpmusuem.net

OK, a bit of history. It was given to me because the previous owner 
couldn't get it to work and suspected a PSU problem. In fact I don't 
think there's much wrong with the PSU (off-load, all outputs are 
correct), I think the logic side was trying to drive one of the motor 
windings hard on, and that was tripping the PSU. 

Currently, I've got it in bits. I've removed all the mechanical side. I 
have the backplane, 4 internal logic boards, HPIB interface and PSU 
plugged together. I've also got the the ribbon cable plugged into the I/O 
PCB and to the front control panels.

I am trying the self-tests. I am assuming they are similar to the ones 
in the -B model, and that all test LEDs on (77(8)) is a pass, for 
example. And that the tests are in the same order and do the same things.

Test 1 (processor board buffers) seems to pass

Test 2 (ROM) doesn't, see below

Test 4 (RAM) passes, even though the darn thing uses 2114s

Tests 5,6,7, (interrupts) seem to pass too

Test 10 (HPIB) passes. And I see little flashes from the 'addressed' LEDs 
on the back, so I think it is doing something to the HPIB card.

OK, back to test 2. This would seem to be a ROM checksum test. It fails 
with error 54(8). It's certainly looking at the ROMs on the ROM/RAM 
(memory) PCB), if I pull that board it fails with a different code 
(which, if the codes are the same as the -B version would indicate that 
the lowest ROM on the ROM/RAM board had failed, which makes sense as it's 
not there when I pull the board).

Now for the problem. if the the codes are the same, then 54(8) is 'ROM 60 
LSB failed). ROM 60 (assuming that's the high digits of the octal 
address, which makes a lot of sense) is a ROM that's not present in the 
-A model (the -B has more ROM, since it can do raster dumps). 

The ROMs are AM9216s. These seem to 2K*8 devices, with 2 chip select 
lines (at least one of which has mask-programmable polarity) and need a 
+12V supply (although not a -ve supply as well).

Does anyone have a service manual for the -A model and can look up this 
error code for me. And assumign it is a ROM failure, does anyone have a 
ROM dump, or a dead machine I can get a chip (or board) from?


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