1 Oct
2008
1 Oct
'08
1:59 p.m.
Very few HP
classic desktop computer service manuals contain scheamtics.
You might, if you are lucky, get PSU schemaitcs, but not for the
processor, etc, sections. I am, of course, trying to remedy this...
That stinks. Anyway, the
HP9836 'service manual' is a boardswapper guide, and contains
very little information that's not obvious from 10 minutes of looking at
the machine. There's a large section on running the diagnostics, with
what to do for each error, and alas the latter is 'repalce the <foo>
board'. And very often those error messages give a lot more information
once you've learnt to interpret them
I've seen some diagnostics that were like that, and some that were much more
specific, telling you what chip you might want to
look at changing out. But
not since the early days of the Zenith Data systems stuff. The trouble with
that sort of diagnostics is that most of the machine needs to be working in
the first place, or they don't load and run. Printed versions of the same
Yes, I don't really trust diagnostics either. After all, the device
producing the report (the computer you're working on) is probably not
working correctly (otherwise you'd not be repairing it) so how can you
trust the diagnostic program output. I prefer to use a 'scope or logic
analyser whenever possible (and when finding the memory problem I've just
desicribed, I did look at the RAS/ CAS/ etc signals first...)
[...]
I've often wondered why there wasn't some
standard way of numbering those.
This sounds like the serial connectors that were out there (and I have a pile
of them) for different I/O adapters, if you didn't happen on the right ones
the serial ports just wouldn't work, and it wasn't obvious why.
The craziest one I've ever seen is on the PERQ. It uses a DB25 connector
for a GPIB port (I am told this is an IEC625 interface or soemthing). The
problem is that it simply maps the pin numbers pin-pin so pins 1-24 are
used and pin 25 in a N/C. This puts one of the date lines on the top row
of the connector after the shield pin (pin 12 is shield, pin 13 is a data
line), it also means you can't simply crib an DB25 plug and a 24 pin
microribbon socket onto a piece of 24 wire cabel to make an adapter. ARGH!
The dismantling procedures in that manual are a
little odd too. Anyone
who can follow the procedure for removing and replacing the internal CRT
of the 9826 and not end up dropping it or using choice language is a lot
cleverer than I am.
I've thought for a long time that "using choice language" was a part of
being
a technician. :-) There's
one curious thing about that servic manual. It contains no
schematics at all. Not even of the mains side of the PSU, which is
trivially field-repairable.
Then they really ought not to call it a service manual, per se. Or at least
not in my view of things. Yup, if you crank it way up.
I _think_ the only misadjustment that will cause this is the A1 ('screen
grid') adjustment on the flyback transformer. Maybe setting the clamps
way too low will do it. for each color. You'd flip a "service
switch" which would give you just
horizontal lines on the screen, and either adjust for all white or if they
Yes, ben there, done that.
On this monitor, the 'clamp' presets on the video PCB prerform
essentially the same function
weren't exactly overlapping for equal apparent
brightness. Or in some stuff
till they just went out.
(Snip...)
How certain can you be that they went and made one that was unique to that
machine?
I cna't be. All it has on it is an HP part number (which is not a lot of
help). I have no idea who actually made it, whether it was used in any
other HP product, or whether it was actually a standard one that was
re-labelled (although I think that is unlikely).
I wonder
if it would be possible to get from some aftermarket suppliers?
I
Als I doubt it. IT was not a common machine, so I doubt anyone bothered
to make a nrw flyback for it.
Different strokes, etc. I suspect that with a little digging it might be
possible to find out who actually made that. They likely didn't make it
themselves. And an off-the-shelf product is much cheaper than one that's
custom-made for one specific product.
THis is HP we're talking about... I would not be at all suprised if it
was a custom part. And even if you could find who'd actaully made it,
they may well be under contract to to release any details. Of course now
it has no real commerical importance, but trying to find somebody at HP
who (a) realises this and (b) is prepared publically to say so is going
to ba lot more work that designing and making a flyback from scratch.
(Snip...)
[Description of monitor horizontal deflction system snipped]
Of course this
information is not in the HP manual...
Of course...
Did you figure most of it out or come across it somewhere else?