2 Oct
2008
2 Oct
'08
9:18 p.m.
On Thursday 02 October 2008 13:52, Tony Duell wrote:
Well, it can be in the hands of some, and I envy those who have that
knack. :-)
As long as I've been working with this stuff there are still surprises for me
now and then.
Which is not the same as saying it were say, IBM. :-)
I am not so sure. HP used a lot of custom parts in their machines. The
earlier desktop machines mostly had custom-designed processors, for
example :
9100 : Custom, and very strange discrete-transistor thing. No ALU, even...
98x0 : Bit-serial 16 bit processor built from TTL chips.
9805 : Arithmetic/Registers and Control/Timing HP custom chips (as in
handhelds), I think
9815 : Motoroal 6800 (OK, standard)
9825/9845/9835 : HP BPC processor custom hybrid module
8x series : HP custom 8 bit procesor (Capricorn?)
9000/200 series (the ones wr're talking about) : 68000, 68010
I would not be at all suprised if HP made/had made custom flyback
transformers.
I will defer to your experience with them, but such stuff makes less and less
economic sense as time goes on. I have no particular feel for the chronology
of these models either, unfortunately.
If I had that much of an idea I wouldn't be asking now, would I?
Ok, OK... Well, if I get information from other sources I do try to give
the reference (to a manual, a website, the person who told me, etc). So
in this case I claim I figured it out myself, given some help from the HP
service manual (connector pinouts), the CE manual (memory map) and plenty
of databooks.
I think that giving credit is a good thing, but too often I can't remember
where I read someting these days...
--
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
On Wednesday
01 October 2008 16:59, Tony Duell wrote:
The former of course, and I don't know why you'd ask me such a silly
question...
Well, sometimes I can be a pedant, and one thing that irritates _me_ is
the fact that English is not a precise language ... > 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.
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? [Graphics PCB RAM chip allocation]
Some engineer got very clever there, it sounds like, and then somebody else
in the hierarchy decided not to let you in on how that worked, in detail...
At least it was possible to figure it out.
Yes. The circuitry is a little odd -- there are 16 4416 RAM chips, and
the data pins are not liked -- effectively there's a 64 bit databus on
that card. Each RAM chip can be written individually from the approprate
4 68K data lines -- there are a couple of '138s which select the
appropriate chip (or pair of chips for a word access -- 2 pixels at a
time) for wriing. I forget how the data is handles for reading, I think
there re 8 off 8 input multiplexer chips which bring the 64 data lines
down to 8, these then go to the appropriate 68K data lines again
('appropriate' here means the low nybble of each byte, so likes 0-3 and
8-11). The decoders and muxes are controlled by the low 3 bits (A1-A3) of
the 68K address bus. The data also endes up in 4 16 bit shift registers (a
total of 8 '166s I
think), which send it a a 4 bit serial pixel stream to the colour lookup
table and thence to the DACs.
I guess this was the easiest way to get the necessary pixel rate from
slow-ish DRAMs.
Having worked all that out, it was still not obvious what diagnostic
error was telling me. Since it occured at the first RAM location in the
graphics RAM (there's a pattial memory map in HP's CE handbook for this
machine), I first looked to see eich RAMs were being written to. When I
found it was only 4 of them, all on the high half of th word. I guessed
the diagnostic stopped as soon as it found an error, and that this was a
simple read/write test. Then, by carefully grounding RAM data pins
(rememebr everything was buffered, so this wouldn't crash the processor)
and seeing how the R: value changed when I re-ran the diagnostic, I
figured it out.
Ah.
Then it was just a matter of desoldering the RAM chip
and fitting a
replacement.
Yes. I spent some time getting my stuff organized today, hopefully I'll be
able to finish that up and get it to the point where I'll be able to start
doing something with all that stuff...
It's a nice feeling, isn't it? I miss
that lately.
Indeed yes!. I love it when a dead machine, or one with a reported fault,
works perfectly again. [..]
Over 10 years ago I bought an HP LogicDart. It was expensive, but I have
never regretted it. I've got other instrumetns that do all it will do and
more, but that's a useful handheld tool that will find 99% of
digital faults in classic computers, if used with that most important
piece of diagnostic equipment -- the thing inside your head.
Yes...
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. I don't
think I've seen many diodes in TO-3 packages. Plastic ones,
yeah.
This is the modern equivalent of an EZ80 or whatever you call it :-). 2
diodes in one (To3) package with a common cathode connection (broung out
to tthe case) and separate anodes (to the 2 pins). It's used for the
classic biphase rectifier circuit with a centre-tapped transformer. I
think I've seen them in DEC machines too. [...]
That's what I was wondering, if there were any possible way to research
that sort of thing.
Did any companies produce catalogues of flyback transformers giving the
winding connections to the pins and the inductance/number of turns of the
windings? If so, it would be possible to see if any of them matched up at
all.
I know that years ago you could by some "universal" type replacements for
flybacks and yokes, but that was a really long time ago, probably mostly
for TV uses, and likely to predate most monitors. Whether that's something
that's been continued since then I can't say, though my feelings are that
since it was done once that shows that such a thing is possible and that it
might've been done again in the intervening years. Although I used to run a
service shop I've not done so for a nontrivial time -- 16 years this past
spring was when I closed it -- so I'm seriously out of touch with what goes
on in that business these days.
> > 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.
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). The 3rd-party suppliers over here will sell you a
flyback for TV model
<foo> or monitor <bar> but they don't give any more details than that.
A generic replacement type flyback? Or an OEM part? If it's the former then
maybe there's some hope.
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... Did you figure
most of it out or come across it somewhere else?
Now, given that I've had this machine in many bits over the last few
months what do you think?