9 Aug
2012
9 Aug
'12
3:14 p.m.
Hi Tony
Quite a long answer but very interesting.
Firstly let's establish credentials. Prior to 1975 when I joined DEC I was a
development engineer and designed with TTL logic. I did a lot of work
interfacing to PDP8's at Harwell and elsewhere. My final job before being
approached by DEC was developing VDU's many of which ended up connected to
11/70 timesharing systems and the like.
I was certainly not criticsing you (or anyone else) specifically. FWIW,
I've seen many of your posts here and I know you know what you are
talking about.
On the other hand Iv'e met DEC field servoids who admit they can't
solder. In fact when an upgrade required soldeirng, I used to do it for
them much of the time (!).
My experience, as you may know, includes HP desktop calcualtors and
computers. You can see the ofifical service manuals on hpmuseum.net.
Apart from the PSUs, there are no schematics in general. The ofifical
proceudre, carried out by fireld engieners, was to swwap boards until it
worked. No real logic to it at all.
Now this time I am not goign to criticise board-swappign _at the time the
machien was in productuion_. That is a separate issue. But now, when the
machine has been out of production for decades, there are often no
knwn-good sets fo board around. Swapping one possibly-defective board
with anohter possibly-defective board is goign to get you nowhere fast.
I am quite sure there are people who worked for DEC, HP, IBM, etc, etc,
etc who did (and stil ldo) know how these machiens really worked and how
to repair them. And such people are, indeed, an asset to a museum. Nobody
is doubtign that. But equally there are ex-employees of such companies
who were field serive engieers but who just vfolloed the boardswappign
instructiuons. And there are hobbyists who have taught themselves how the
machines work and how to fix them. IMHO the latter are more valuable than
the former now (although the input from both is worthy of consideration).
Alas most, if not all, meuseums, want the former and not the latter.
Put it this way :
Person (a) worked as a calcualtor field servie engineer for HP from 1970
to 1975. And has not touched such a machine since
Person (b) never worked for HP ro any other computer compny, But he's
produced hs own schematics, commented microcode soruce, etc for the
HP9800 machines. Oh, and written a repair guide.
Now, who do you want working isnide your HP9830?
-tony