1 Oct
2008
1 Oct
'08
2:55 p.m.
On Wednesday 01 October 2008 16:59, Tony Duell wrote:
Waht does? The fact that HP desktop computer service manuals are anything
but, or the fact that I am trying to do soemthing about it?
The former of course, and I don't know why you'd ask me such a silly
question...
THe HP ones are pretty specific. For example, this machine had a
graphics board problem when I got it, the error would be reported as
'graphics failed Meory failed at <hex number> W : <hex number> R :
<hex
number>'
Not bad.
YEs, but I tend to reserve it for when it's really needed. Like when a
30kV supply flasehs over to my hand, or I drop the power transformer on
my foot.
Yes, that sounds like situations that would call for it all right. But that
may be a bit more reserved than I tend to be. :-)
Exactly...
For information, the PSU is bascially as follows. Mains comes in on a
filtered IEC plug, goes through the mains fuse and then to the power
switch under the keyboard. From there it goes to a little PCB screwed ot
the (inide of the) back panel of the machine which contains a pair of
ovltage sleector swithces. THese link to the primaries of the mains
transformer (2 windings each 0-100-120V, the switches let you configure
the machine for any of the normal mains voltages). There is a single
centre-tapped secodnary on the transformer, this goes back ot the PCB
which contains a pair of small diodes used to provide a power-fail
indication to the optional battery backup unit and a large double-diode
unit (TO3 can) for the main supply.
I don't think I've seen many diodes in TO-3 packages. Plastic ones, yeah.
Ok.
That's what I was wondering, if there were any possible way to research that
sort of thing.
Which is not the same as saying it were say, IBM. :-)
Now, given that I've had this machine in many bits over the last few
months what do you think?
If I had that much of an idea I wouldn't be asking now, would I?
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
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 It was a good bet those 3 hex numbers were an address,
the value written
and the value read. THe only problem was that the W anmd R numbers were
32 bits each (8 hex digits), the 68010 processor used in this machine [1]
has a 16 bit data bus. Worse than that, the graphics memory uses the low
nybble of each byte only -- this is to allow writes to individual pixels,
there being 4 bits per pixel. So even knowing which bits had failed it
wasn't immediately obvious which memory chip to change.
At least it was possible to figure it out.
In fact, after much testing, I discovered that 4 of
the hex digits are
always 0 (these correspond to the nybbles that don't actually exist), the
other 4 nybbles are either all parts of high bytes or parts of low bytes,
and these 4 nybbles correspod to different RAM chips on the PCB (there
are 16 4416 RAMs on the graphics board...) having figured that out, I
desoldered the chip I thought it was complaining about, replaced it (with
one raided from an old EGA grapghics card) and was pleased to see that
the graphics now passed diagnoistics
It's a nice feeling, isn't it? I miss that lately.
And no, none of that is in the HP service manual
either. If they'd
explained how to decode the error message it would have saved me an hour
or so's work
[1] Yes, I know everyone claims it's a 68000 processor. This machine has
a 68010 and an MMU circuit. It's the latest (AFAIK) version of the CPU
board.
I guess it all depends on the nature of the fault.
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...)
The scope was my most-used tool for that sort of thing, and I never had the
use of a logic analyzer, mostly working for myself I could never justify the
expense. Lots of positive aspects to being self-employed, but there were
occasional negative aspects too.
[...]
Even with the standard pin and serial connectors there are apparently enough
different ways to put them together to cause problems.
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. The output of this is smoothed by what a frield of
mine would call a CFE
(Capacitor F-ing Enormous) to provide about 30V DC. This is fused (15A) and
fed to an edge connector socket screwed to the bottom of the case. One set
of fingers on the PSU regualtor PCB plug in there -- this PCB contains
step-down switching regulators providing +5V, +12V and -12V. The outputs of
those go to more edge figners which plug into a connector on the
motherboard.
I notice that edge connectors are a lot less common than they used to be. I
wonder if there are reliability issues by comparison with other typies?
The battery backup option was an 18V (?) NiCd (?)
which fitted into a
cavity on the bottom of the machine and which provided an input to the
regulator board.
That'd be what, 15 cells? Yikes!
There was an extra control PCB that munted under the
(RH) disk drive, I know
little about this apart from the fact that it appears to have contained an
8041 microcontroller. The battery unit is one of the rew options I don;t
have for this series of machines.
Screen controls are singular these days, but the early stuff used to
have one
Yes. In fact this CRT has separate cathode pins for each colour, but for
all the other electrodes, corresponding ones are linked inside the CRT
and brought out to one pin.
I'm pretty sure that was one of the changes when they moved away from the
original delta arrangement.
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.
Maybe so. And I could be totally wrong about this, but I just feel like
there should be some way to characterize those, somehow. Maybe not, but
maybe I'll play around with the idea at some point.
(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?