29 Sep
2008
29 Sep
'08
5:22 p.m.
On Monday 29 September 2008 16:28, Tony Duell wrote:
(Snip)
Ok. I have really run across very few occasions when this stuff was that
critical. One instance was a photo-processing machine, you'd put a color
negative on a stage and twiddle the knobs until it looked best, and the
settings on the knobs would tell you what filter you might want on the
enlarger or how you might alter processing a bit, stuff like that. It was a
Trinitron monitor and that wasn't where the problem was, they had an 800V
(supposedly) regulated supply for the photomultiplier tubes that had a minor
issue that I fixed.
And the
adjustments you talk about are not really all that critical
either. I've done them, bunches of times, as a matter of normal service
routine, back when I was working on that sort of stuff.
Nrmally I'd agree with you (adter all 'colour temperature' was a user
adjustment on a lot of PC monitors). It becomes critical if you need
accurate colour reproduction (e.g. for TV studio work). But what worries me is a comment in the HP service
manual. It basically
warns you not to twiddle these adjustments (the same sort of message is
printed on the metal cover over the monitor chassis).
I lost a great deal of trust in their stuff some time ago when I ordered
a "service manual" for some H-P product and received a very small bundle of
paper that was shrink-wrapped, and on opening it I found "The monitor is
normally not repairable, but is replaced as a unit..." I sent it back and
told 'em I wasn't going to pay that particular invoice as that was of
absolutely no use to me whatsoever. :-)
And that misadjustment can cause various problems :
Visible flyback lines
Yup, if you crank it way up.
Missing colours
If you don't have it turned up high enough.
Incorrect colours (compared to another 9836C)
Either of the above.
Significantly decreased reliability
Maybe if you crank them _all_ up?
Now, the first 2 are very ovbious, and I'll not
have problems with that.
The third doesn't bother me at all, since I only have one HP9836C. But
the last does worry me.. Particularly if the part that fails is the
flyback transformer. The CRT seems to be a standard one (I can find no
data on it, but some CRT testers/boosters list it as one of the CRTs they
can handle). I would have a chance of finding a replacement. The
transistors on the video board are all standard, so I could find
replacements. But HP never supported component-level repair on these
machines, and the flyback transformer was only avaialbe as the complete
deflection PCB. And that's long unobtainable.
I wonder if it would be possible to get from some aftermarket suppliers? I
had a number of different video products that I ended up working on, in
spite of my inclination not to back then. One that comes to mind is "BMC",
which I think may possibly have stood for "Best Monitor Company" or somesuch,
though they also made printers and other stuff. We're talking composite
input here, and 9-pin dot matrix, and I think I still have the service
manuals for those. Anyhow the common problem with the monitors was an STR
(some numbers) regulator chip, but I also ran into a couple of them that had
bad flybacks, and was actually able to obtain and fix one, the guy who had
the other deciding that it was too much money (so I kept it for parts). I'm
not 100% certain, but I may have gotten that from an outfit called MCM
Electronics, which seems to still be around although they now seem to be
owned by Newark. There are probably others, I remember catalogs from a
bunch of those places back when.
I don't if any other HP monitor used the same
transformer -- the horizontal
scan rate is unusual -- about 25kHz -- but other HPs used the same sort of
rates.
The scan rate supported (with the flyback time being the proper portion of a
scan line and such) is not only determined by the transformer but also by
what all else is hooked up to it, capacitors in particular. And HV
regulation ties into this too.
I can't imagine H-P deciding that they were going to make their own flyback
for this one monitor as opposed to using something else that already existed.
Not impossible, but it just doesn't seem too likely to me.
--
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