How to lose most of an an entire collection in one shot

Tony Duell ard at
Sat Jun 20 13:07:18 CDT 2009

> > Repairing them is interesting, Most parts, the exceptions being the HP 
> > custom ROMa and the Intel 1103 DRAMs are easy to find. But being a 
> > bit-serial machine, tracing the fault is hard without a logic analyser (I 
> > speak from experience having repaired several 9810s, a 9820 and a 9830).
> >   
> Yes, I noticed that at the time.  This was before microprocessors.  We 
> were going to go with the replacement guarantee...

That's not a lot of help _now_ (and nor is board-swapping, whatever your 
moral views on doing it. If you can't get known-good working boardsm you 
can't swap them).

In fact HP put a test connector inside on the CPU control (microcode) 
PCB. Amongst other things it carries the 8 bit microcode address. Looking 
at that -- even just seeing if it executes certain microinstructions -- 
is a great help in debugging a faulty machine. Well, provided you 
understnad the processor and have the microcode listings it is :-)

> > How on earth did that happen?
> >   
> I fell in love with a woman living on the Big Island of Hawaii.  That's 

Oh I see.... :-(

>  From this point, for the foreseeable future, MY hobbies have to be 
> pretty cheap, or involve stuff I already have.

I, alas, have the same problem for rather different reasons (no ladies 
involved...). Fortunatley when I had spare money, I bought good tools and 
test gear, and I've got a numnber of machiens around that need reapiring, 
so I'ev got plenty to keep me busy.

> > Yes, older HPs are well-built and often well designed (although I am not 
> > convinced the HP120 is a particularly good design for a CP/M box). I feel 
> > the peiod from about 1965 to 9185 was the 'glory days of HP' when they 
> > had some wonderful products. If I can get stuff from that period, I do..
> >   
> I agree on the HP-120, but the HP-125 actually is very nice.  One of my 
> favorites, AaMoF.

What's the difference? I am serious. Apart from the keyboard interface, 
they're pretty much the same machine, just differently laid out. Even the 
ROMs are the same between the HP120 and one version of the HP125. The 
keyboard interface is physically very diffeernt, but the keyboards are 
logically fairly similar, to the extend you can use an HP125 keyboard on 
an HP120 with a 3-chip circuit (all 4000-series CMOS parts), although the 
reverse is a lot harder.

OK, there's no official way to have an internal printer in a 120, but the 
interface is there, and althohgh I've not tried it, it should work. One 
day I'll borrow bits fro man HP150 and see. 

When I said I didn't like the design of the HP120, I didn't mean the 
'looks ' of the machine. I meant the electronic design -- a separate 
terminal processor communicating with the application processor through a 
little 'mailbox' and a very strange video circuit.


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