HP 9845 C with 280 option startup failure

Tony Duell ard at p850ug1.demon.co.uk
Wed Oct 26 18:38:11 CDT 2005

> >> 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.

I haev no idea what the Option 290 is either. In fact I don't even know 
what I have -- I know it's a 9845B with the high-speed language 
processor, 2 tape drives, intenral printer, 1 256K word RAM board (and 
the usual 2 RO</RAM boards), and a 98780 enhanced mono monitor.

> Actually, there was a supplement for the model 200 line for that manual 

Yes, I've seen a reference to it. But it's not on the hpmusuem.net site, 
and AFAIK the owner of said site doesn't have it. 

It's probably not that useful. It won't contain scheamtics. It won't 
contain other usrful info like the pinout and use of the test connector. 
We all know how to remove and fit the assembly, and how to separate it 
into the 3 boards and the backplane. 

> 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 

OK, not 2901s, but not ASICs either. The 1820-2377 is an AM2903 (which is 
somewhat like a 2901, a bit-slice ALU + registers), the 1820-2378 is an 
AM2910 sequencer. Interesting...

> images.

Alas pictures do not repsond to continuity testers and logic analysers :-)

> 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.

I am pretty sure the video interfave board (the left-hand board that 
connects to the monitor) is different. It's the same for the enhanced 
mono and colour monitors, but the standard monitor uses a different one. 
I have no idea if it does any damage to use the 'wrong one'. But even if 
not, presumably there are differences, which may cause errors/problems 
(exactly what you don't need when looking for a fault!)

> 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".

It's worse than that. You replace boards until the machine appears to 
work again, then put back the old ones to see if it stops working. No 
real diagnostics at all. And you wonder why I think that manual is a 
waste of trees...

> 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 think similar ROMs were used in other devices. The HP9815 (I think the 
-S version, the one with 4K RAM on the CPU board) uses 8K ROMs with 
internal address latches.


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