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Old 16th Aug 2019, 9:19 pm   #1
blakeyboy
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Default Unknown Barco 26" rebuild

I have a Barco monitor, originally with just a start in, with the usual early '80s
'Guess which pin it is' game. I've just re-capped it, and I'm trying to align it.
i used to fit Barco video projectors, but my knowledge of monitors is limited.

I would love a picture with a bit more 'life' in it. The picture was excellent for years- I was told when I got it in the late '80s that it was a Grade 2 monitor, and have heard that since, though how true that is....

Two problems. I have no idea what it is, so I can't ask anyone for info/ schematics/ alignment notes.

I also have a bit of a convergence problem at the bottom right corner, but the tube neck (ITT A66) has no rings....

this is my first attempt at posting pictures so fingers crossed....

Regards

Blake.
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Old 16th Aug 2019, 11:30 pm   #2
toshiba tony
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Default Re: Unknown Barco 26" rebuild

Didn't these use a 20 or 30ax system? I'm way past it now, recently retired but memory tells me convergance was minimal.
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Old 17th Aug 2019, 2:20 am   #3
linescan87
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Default Re: Unknown Barco 26" rebuild

Looks like a 30AX type tube to me.
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Old 17th Aug 2019, 6:33 am   #4
Sideband
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Default Re: Unknown Barco 26" rebuild

It is a 30AX tube so there are no convergence controls. Essentially they were 'convergence-free' colour tubes. The scan coils are matched to the CRT during manufacture and are generally considered as one assembly and bonded to the CRT. When these were used in domestic TV's it was considered 'acceptable' to have minor convergence errors in the extreme corners. Generally these errors were only really noticeable on things like the teletext clock.

Presumably when these tubes were used in computer monitors the tolerances were tighter to give less convergence errors. Possibly it's a 'grade 2' because it didn't quite 'make the grade' but was acceptable for less critical applications like a public announcement display.

That PCB doesn't look like standard 'monitor quality' build unless you've removed a lot of screening covers. It looks more like a 'cut-down' TV with just the video and timebase circuits. I suspect it wasn't a particularly expensive model.
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Old 17th Aug 2019, 10:55 am   #5
hans
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Default Re: Unknown Barco 26" rebuild

These tubes have only one adjustement. That is the potmeter on the yoke. I never had to adjust any, so I can't say how that works, but I think it is vertical static convergence. The 30 AX tubes were never 100% converged, as most of the "unadjustable" tubes are/were.

I have had many bad experiences with ITT/SEL tubes. They wore out fast and gave unfocused pictures. Philips used to be much better, except for some types that died very fast. The 30 AX tubes could give a very good picture when working correctly.
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Old 17th Aug 2019, 10:55 am   #6
blakeyboy
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Default Re: Unknown Barco 26" rebuild

Quote:
Presumably when these tubes were used in computer monitors the tolerances were tighter to give less convergence errors. Possibly it's a 'grade 2' because it didn't quite 'make the grade' but was acceptable for less critical applications like a public announcement display.

That PCB doesn't look like standard 'monitor quality' build unless you've removed a lot of screening covers. It looks more like a 'cut-down' TV with just the video and timebase circuits. I suspect it wasn't a particularly expensive model.

Thanks for this...

I always understood 'Grade 2' to be better than domestic (Grade 3) and one down from broadcast (Grade 1). is this correct? For years this monitor blew away all my friends' sets, and I only stopped using it because of it's depth about ten years ago. Cheap flat screens were a comedown after this set...

yes- it does look like a stripped down unit to just do video, but the on off switch was originally on the back panel, so the case is just enough to house the tube, and no front control space at all, so made for use as a monitor. I got it as the spare for a nightclub video wall in the late '80s..
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Old 17th Aug 2019, 2:13 pm   #7
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Default Re: Unknown Barco 26" rebuild

Could it be a Hantarex monitor?
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Old 17th Aug 2019, 4:52 pm   #8
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Default Re: Unknown Barco 26" rebuild

Probably not if it's a Barco (does it say anywhere on the set it's a Barco?), unless they bought low end sets from Hantarex. It looks like a stripped down TV set, did Hantarex ever build TV sets? Barco did, with similarly looking chassis.

About the convergence: 30AX tubes have their static convergence and purity rings as neck-internal components, magnetised "for life" at the end of the manufacturing process. The dynamic convergence is achieved during the mounting of the yoke. Depending on its construction, it can be tilted and refixed if necessary, but this is only a last resort. You can also achieve corner convergence by sticking plastic strips with small permalloy pieces in between the yoke and tube. Sony used them a lot but they can be found in various older computer monitors as well.

Last edited by Maarten; 17th Aug 2019 at 5:12 pm.
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Old 19th Aug 2019, 7:09 am   #9
Synchrodyne
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Default Re: Unknown Barco 26" rebuild

Quote:
Originally Posted by blakeyboy View Post
I always understood 'Grade 2' to be better than domestic (Grade 3) and one down from broadcast (Grade 1). is this correct?
That’s my understanding. When I looked into that classification system a while back (admittedly not very deeply so) I gained the impression that it was purely a qualitative grading, without any associated quantitative limits. Although I imagine that there are quite tight specifications associated with broadcast monitors, written by broadcasters and broadcaster organizations such as the EBU.

Quote:
Originally Posted by blakeyboy View Post
yes- it does look like a stripped down unit to just do video, but the on off switch was originally on the back panel, so the case is just enough to house the tube, and no front control space at all, so made for use as a monitor.
My recollection is that in the later 1970s and into the 1980s Barco used common basic chassis for its grade 2 receiver-monitors and monitors. For example, the CRM2632 was a (multistandard) receiver-monitor, whilst the CM2632 was a monitor.


Cheers,
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