29 Oct
1999
29 Oct
'99
11:53 a.m.
please see embedded remarks below.
Dick
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Friday, October 29, 1999 12:21 PM
Subject: Re: HELP! ( totally OT) - Hitachi Monitor problem
very
I wish I knew as much about these things as you, but I've stuck with the
circuits inside the computer, and allowed others, (obviously) to worry the
problems with monitors. I learned at an early age, that punched and screwed
chassis take skin of hands (or whatever else you have on their far side) as
you try to get away from the "bite" of the HV lurking inside.
> >Hey _I'm_ the one that flames about not
being able to get service
> >information for everything I own. Last time I ranted on about this you
> >pointed out a number of good reasons why such information might not be
> >available.
> >
> It's like getting the service manual for a car of the same vintage,
except
> that when a car is this old, it's just
starting to cause little problems
and
> the third-party repair manuals are available
everywhere. In the
electronics
ALthough to be fair, most of the 3rd party car shop manuals are a waste
of space. Having been caught out a couple of times, I now always work
from the factory manual. It costs a bit more, but...
Agreed, though the original from the mfg is normally only available during
the first year or two of ownership. I have the Nissan manual for my Maxima,
though it was nine years old before I needed it. Frankly, I bought a 3rd
party manual only because I couldn't find the original.
> business, there have never been really decent repair manuals from 3rd
> parties, except maybe for TV's, of which I've never had one break.
> Unfortunately, as the prices of these commodities drop, the level of
> expectation to which the vendors respond drops as well. These days, you
can
> get a really decent 20" monitor for $400 or
less. When it breaks, it's
> unlikely you'll get anyone to fix it for less than the price of a new
one.
Except that in a lot of cases the old (and expensive when new) monitor
(or whatever) is built a _lot_ better than the modern 'replacemnt' (and
it may well give better performance as well -- a lot of modern monitors
have terrible convergence, etc).
I guess I'm strange, but I'd rather repair something that was once great
than replace it with something that could never be as good...
Yes, but new monitors these days have flat screens and are VERY sharp and
VERY linear, unlike the large-screen multisync displays of yesteryear. The
fixed frequency varieties which are so difficult to use for anything useful
are the outgrowth of this. Instead of making an "average" monitor with the
ability to sync at several sweep rates displaying appropriate resolutions,
they made one which was VERY linear and VERY well focused and converged at a
single frequency and let the boardmakers benefit from that.
If you want a schematic of a 7-year-old TV set, I doubt it's readily
available either. I've never had a monitor repaired successfully by a
Hmm... In the UK there were books produced every year of TV schematics. I
have an almost-complete set from 1952 to 1981 (!) -- these ones cover
radios, tape recorders, etc as well. And beleive-it-or-not, many public
libraries have at least some of them available.
So finding the schematic of a 7 year old TV (which is not an old set
IMHO) would not be a big problem.
There are also companies who sell copies of old service manuals, for just
about anything. I got the manuals for the Sony 'Rover' portable
reel-to-reel video recorder and camera a few months back. That thing is
over 25 years old, but there was no problem in getting a service manual,
although Sony could no longer supply it.
Said company does sell computer (mostly home micro) and monitor service
manuals (I got the Sharp MZ80B manual + schematics from them). But
obviously they can only supply manuals if the manufacturer of the device
has produced them (and has given permission for them to be reproduced, I
guess).
There are some books of computer monitor circuits available, and then
later they produced similar information on CD-ROM (basically just scans
of the manuals). I found the latter to be painful to use, but the former
are actually very useful. Even if your monitor isn't in there, there's
likely to be something that's similar.
> "professional" working at an "authorized" repair center. I sent
in a
I've never met a 'professional' who could repair anythign of mine. Why
do you think I fix everything myself :-)...
Hear! Hear! ...
[...]
> >Although it's hard to imagine anything particularly clever/unusual in a
> >standard colour monitor. Most monitors that I've worked on use pretty
> >much standard circuitry.
> >
> That's what puzzles me about the color displays I have sitting about.
There
> aren't many that look even remotely similar
beyond the most superficial
> observation. Not one has a flyback transformer, and all the
> current-generation multisync types use some encapsulated device about
4x6x1"
or so to
effect the power management functions.
Hmm... In my experiece most single-freqeuncy monitors still use a
traditional flyback transformer. I say 'most' because there are one or
two that I have that use an independant EHT supply.
As soon as you get to multiple scan rates (even just for EGA), it makes
life a lot easier if you separate the EHT generator and the Horizontal
output. EHT still comes from a 'flyback transformer' but it's not
connected to the HOT. It has its own driver transistor. Both the HOT and
the EHT-transformer output transistor are driven by the horizontal
oscillator but the supply to the output stage (normally) is separately
controllerd. This allows non-interacting EHT regulation and width
control, I guess.
No idea what modern multisync-with-power-save+... do. I've never had the
misfortune to have to really repair one. The couple I have fixed have had
obvious faults that I could sort out without a schematic and without
understanding how the unit really works. You know, faults like dry joints
on the CRT base.
Unfortunately those are commone enough to motivate even me to look inside.
-tony