25 Oct
2005
25 Oct
'05
2:35 p.m.
I recently
acquired a HP 9845C option 280 (was looking for it for a
really long time).
I don't know all the option codes for the 9845. I assume at least this
has a 98770 colour monitor nad the high-speed (bit-slice) language
processor option.
Firstly, try contacting the HPCC secretary, Dave
Colver (I think the
details are on the HPCC web site, http://www.hpcc.org/ , if not, ask me).
If you ask him nicely, he might send you a reverse-engineered schematic
for the 9845. This is for a 9845B with the high-speed lagnuage processor
and the 98780 enhanced mono monitor, so it's not directly applicable to
your machine, but it might be a start. Be warned that it's over 200 pages
long (that is _just_ a schematic).
The HP service manual is on http://www.hpmuseum.net, along with a manual
for the colour monitor. These do not seem to cover the high-speed
language processor at all, and they are boardswapper guides with no
schematics or even pinouts. But you probably should read those too.
Actually, there was a supplement for the model 200 line for that manual
which covers the high-speed processor in chapter 5 (HP part no.
09845-92030). Unfortunately, this document will be for sure hard to find
(or even lost forever...)
I would love to see inside the colour monitor (that
is, I'd like to pull
one apart and really examine the boards. I am told there are some 2901's
in there for the video processor. The 98780 mono monitor has an HP 64 pin
ASIC for this.
Yes, the 98770A has a couple of AMD ASICS for the vector processor.
However, not 2901 like the bit slice processor, but three 2377 plus one
2378. If you like to get a view on the boards, I can send you some hires
images.
The machine is
in an overall good condition, however it hangs during
memory test ("MEMORY TEST IN PROGRESS"), even after cleaning all board
connectors, resocketing all ROMs & repeated control-stop's. Before
Hmmm... Probably toally irrelevant, but there's a signal from the monitor
to the I/O processor -- basically a frame-rate interrupt, that IIRC has
to be present for the bus arbitration to start up properly. If you run
the machine without a monitor there's a turn-on fixture that you have to
plug into the LH monitor connector (on the video interface PCB) to
provide this.
entering nirvana the printer outputs a couple of
memory addresses.
Although lots of defects may be responsible, I assume there is a
combination of both a bad RAM chip and a ROM failure, since a RAM defect
alone should (?) not crash the system during the test.
Maybe... Maybe not...
How much do you know about the buses of this machine? It's not at all
simple. There are 2 processors -- the PPU (Peripheral Processor Unit) on
the left side and the LPU (Language Processor Unit) on the right side.
Each processor has buffers/latches on the board that connect it to one of
2 buses (I think HP called them X and Y, I call them L and P for obvious
reasons). The L bus carries all the memory on the LH boards, and the ROMs
in the RH drawer. The P bus carries all the memroy on the RH board and
the ROMs in the LH drawer (I think I've remembered all that correctly).
Also, the test side of the video display does DMA from main memory via
the buffers on the PPU board, it transfers a line of text at a time to
buffer storage on the interface PCB and thnece to the text board in the
monitor.
What I am wondering is that if there's a bus problem, or the arbitration
logic (which is spread between the 2 processor boards) is playing up, you
could get some really odd failures.
The printout looks like this:
000000 100112 052525
000000 110112 052525
000000 120112 052525
000000 130112 052525
I guess the first number is the block ID, the next is the memory address
within the block, and the last number is the test pattern, each in octal
representation.
Does anyone have an idea
- how to really interpret the memory test printouts and
Alas not, and I don't think there's anything in the service manual. The
schematic would at least relate addresses and bits to actual chips.
- how to check the ROMs for bad data?
Maybe there is anyone out there who did the job to read out the contents
of his 9845 ROMs (they are all in sockets) for a direct comparison.
I haven't done yet. What I can tell you is that these are not totally
standard ROMs, they have internal address latchs (the buses on the 9845,
like that of the 9825, being multipexed address and data). You ahve to
deassert and reassert the chip select line after changing the address to
latch the new address in.