HP9836C colour alignment (grey scale tracking)

Tony Duell ard at p850ug1.demon.co.uk
Mon Sep 29 15:28:37 CDT 2008


> 
> On Sunday 28 September 2008 18:19, Tony Duell wrote:
> > > On Sunday 28 September 2008 13:20, Tony Duell wrote:
> > > > For those wondering what the current state of this monitor is, I've
> > > > cleaned up all the case parts and put it back together. It still works
> > > > (so I didn't do any damage taking it apart), although there are still
> > > > red fringes to the right of (say) white objects.
> > >
> > > If it were a convergence problem you'd see fringes of the opposite color
> >
> > Exactly.I've not looked carefully enough to see this (I think a magnifier
> > is needed), but I don't think the complementary colour fringes are there,
> > which implies to me that it's an amplifier problem.
> 
> If you don't see it without a magnifier you don't have a convergence 
> problem.  :-)

The red fringing is noticeable without a magnifier. Black-on-white text 
isparticularly bad -- a 'l' would almost appear as red on white. But I 
don;t nitce any cyan fringing in such text.

I would not normally bother to correct a problem that was only visible 
with a magnifier, but it's useful to use one to attempt to identify what 
the problem really is.

[...]

> 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). And that 
misadjustment can cause various problems : 
Visible flyback lines
Missing colours
Incorrect colours (compared to another 9836C)
Significantly decreased reliability

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 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.

-tony



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