HP 9845 C with 280 option startup failure

[Tequi Lizer]

>> 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.
>   
Exactly. The 280 option was like the 290, less the database development 
& the datacomm features.

> 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. 
>
>   
The machine behaves with color monitor installed exactly the same as 
without monitor. So the IIRC may be a candidate. I have another 9845A 
around, but I'm not sure whether a 9845C can be combined with the 
monitor of a 9845A without harm, although the interface is technically 
similar.
>   
>> 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.
>
>   
Well, I wonder how a service expert could get around with the "service 
manual". Probably HP practiced a philosophy just like "those beasts are 
expensive enough, just exchange the complete assembly".

>   
>> - 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.
>
>   
I wonder whether the ROMs are the same types used widely in HP measuring 
equipment. An example can be found under 
http://bama.edebris.com/manuals/hp/3456a/

I'd like to give an eprommer a try to read out the content, as soon as I 
have built a small adapter for this. The ROMs are worth for getting 
backup'ed.


-- Ansgar