Advice re: broadcast CRT repair

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agrajag184
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Joined: Sat Jul 10, 2021 2:23 am

Advice re: broadcast CRT repair

Post by agrajag184 »

Hi all,

Long time lurker, first time posting here. Sorry about the long post!

I recently got a great deal on a Panasonic broadcast CRT monitor - an AT-H2005D, which I can't find much about online. Frustratingly, as it was bought during COVID times I wasn't able to go and test it in person before picking it up (the previous owner sent me pictures of e.g. an inbuilt test grid for geometry and some colour images so at the price I thought it was worth taking a punt on). It turns out it has a couple of hopefully minor problems. As I'm not to keen to go messing about inside, I thought I'd ask here if it sounds like the problems it has are likely to be easy for a local CRT repair guy to fix if needed (or if there is anything obvious I haven't tried.

Firstly, and most importantly, most of the geometry potentiometers in the slide-out tray behind the controls don't do anything. H-Cent and V-Cent work, as does Over-Height, but the Width, Height, and Over-Width ones do nothing when turned. This means that I can set up vertical overscan correctly, but the image is wider than the CRT - on the 240P Test Suite's grid pattern I lose all of the red squares and about half of a white square on each side. It is just enough to cut out important content in games on various systems. I believe I've read online that this sort of issue is generally due to a capacitor somewhere relating to those adjustments having failed, and so is fairly straightforward to fix if one can get the service manual / diagrams - does this sound like it is the case? Also, is there any external way to modify the signal to overcome the width issue (some sort of inline signal adjusting box from Extron etc.) as this might be easier than getting the TV serviced?

Secondly, there is a bit of symmetrical inward bowing on both sides. Not sure if there would be linearity adjustment or similar hidden somewhere inside the chassis but there is no control for this in the external / slide-out controls.

Finally, it often fails to start when first powered on - the yellow activity light at the top flickers a couple of seconds, and then it loses all power and won't power up until I wait about half a minute, then power cycle it. It then is fine to be switched on and off, and is rock solid in use, but after a few hours switched off the problem comes back when it is next powered up. I presume there is some sort of power supply issue, and it would be unfortunate if I got everything else working and then that failed completely and rendered it unusable.

I've got photos of the geometry, all the external controls, and the slide-out tray, if those would help - can't see any way to attach them, however. Can link to my Dropbox or similar if that is allowed on this forum.

Cheers,

agrajag184
masek
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Joined: Sun Dec 10, 2017 8:16 am

Re: Advice re: broadcast CRT repair

Post by masek »

Hi,

This forum (and many others), seem to be pretty light on CRT repair advice. Unless you're looking for the obligatory, "you reach in side there it could kill you" advice. Which usually refers to the 30kV (or thereabouts) FBT - while you keep yourself far away on the opposite side of the chassis right over top of some large filter caps in the power supply (which has a much higher chance of being fatal if charged).

Anyway, the obligatory
*** Do at your own risk disclaimer ***

I had a very similar problem (your power issue) with dedicated power supplies that changed based on temperature and humidity. It turned out to be a loose connection / bad joint. Maybe a good place to start is the power supply section. You could visually inspect leaking capacitors that could be causing a short as well.

If you decide to work on it yourself, you can probably get some large resistors to bleed large (200-400V) filter caps in the power section from the "tube store" in a bleeder resistor / circuit is faulty. If you are serious about testing/probing the CRT full circuit, most advice I've found says to invest in an isolation transformer.

Sorry, it's probably most of the same old advice you've heard before. But, based on my experience, your first problem sounds like a power supply issue. This will have plenty of downstream impacts if out of spec.

Good luck, and let us know what you find. It may help me or someone else find their own CRT issues.
MKL
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Re: Advice re: broadcast CRT repair

Post by MKL »

Issue 1 (picture too wide) and 2 (pincushion distortion) are in fact the same problem. It's not too hard to figure out what is causing it if you know how to use a multimeter and a soldering iron. If not a TV tech will be able to fix it.
agrajag184
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Re: Advice re: broadcast CRT repair

Post by agrajag184 »

Thank you two for the replies - very helpful.

MKL - good to know that it should be fairly simple, and it makes sense that width and the pincushion distortion are linked - however intresting that a broadcast model doesn't seem to have any external adjustments other than width and overscan - I'd figured the stuff that is in software in newer CRTs like linearity, pincushion, trapezoid, etc. would also have been on accessible pots/knobs somewhere. Anyway, I'm not too game to get inside a CRT at this early stage in the hobby and with limited electrical repair experience, so I've now contacted a local TV tech who reports they have CRT experience, and will quote a repair fairly inexpensively so I won't lose too badly if it turns out to be something more complex or unfixable. The main thing I was wondering about was what the most likely cause of a selective failure of a few geometry adjustment pots on the control panel would be, as this appears to be the cause of it being overly wide - from playing with the vertical adjustments the amount of horizontal overscan it is stuck on seems to be about as much as the maximum I can set the vertical to. Hope it is something as simple as a dead capacitor somewhere.

masek - whilst they are in there they'll no doubt check if there are power supply issues. On the upside, it turns out that if I hold the power button for a couple of seconds when I first turn it on this seems to avoid the odd not turning on behaviour that was happening before, so perhaps the power supply is actually fine.

If I'm getting a tech to look inside an old and fairly high-value CRT like this, if I'm wanting to keep it in the longer term, is there anything else pre-emptive I should specifically request they check and/or work on prior to other components failing down the track? I presume that any leaky/failed capacitors will be checked and dealt with whilst they are in there regardless, but is there anything else important that might not be standard if I don't ask for it?

Thanks for all the help!
MKL
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Location: Pordenone, Italy

Re: Advice re: broadcast CRT repair

Post by MKL »

agrajag184 wrote:The main thing I was wondering about was what the most likely cause of a selective failure of a few geometry adjustment pots on the control panel would be, as this appears to be the cause of it being overly wide - from playing with the vertical adjustments the amount of horizontal overscan it is stuck on seems to be about as much as the maximum I can set the vertical to. Hope it is something as simple as a dead capacitor somewhere.
It's either the transistor that outputs the pincushion correction signal or a diode further down the same path. A few other things are possible but less likely.
masek
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Re: Advice re: broadcast CRT repair

Post by masek »

I'm not sure what goes as standard in the CRT repair business, but electrolytic caps have a shelf life of what? 15-20 years unused at spec? If that's the case, some of our Nichicons are on borrowed time :)
Anyway, the point is, if they would do it (and I don't blame them if not), just go ahead and replace all of the electrolytics if not cost prohibitive. It would give me peace of mind; but maybe not entirely necessary to maintain a good picture for a good bit. I'm not familiar with your monitor, though. I know if I asked someone to replace them all in mine they would probably shut their doors.

In addition, if your purity is off, you could ask them to get that in line while they have it open. Doesn't sound like you are noticing any issues with that though (probably rare issue on a broadcast quality monitor). And if that's the case, best to not make any adjustments to that at all unless it's really noticable(good story for another post). But if you do make adjustments to it, make sure you/they make them with the monitor facing the exact same cardinal direction it will face in your home.
agrajag184
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Re: Advice re: broadcast CRT repair

Post by agrajag184 »

That's an interesting thought. Does anyone else here have a different feeling about recapping everything now vs waiting for more caps to fail and dealing with them then?

Also, a quick question about a different problem I have with another CRT - a small Sony PVM-1300 that I understand probably dates back to the late 70s and which I got inexpensively in an eBay auction. Its RGB gain and bias are adjusted by three pairs of pots on the front of the TV. I've found that the red and to a lesser extent the blue go haywire if I turn them up too high - the entire screen basically pulses in the colour in question at extreme intensity until I turn them down. Furthermore, even at lower settings, they will do this intermittently when certain things happen on screen (haven't quite figured out the pattern yet but changing scenes in games sometimes set it off), particularly in the few minutes after the pot was touched to adjust the setting. Does this suggest something easily fixable or something major (like the gun for that colour) being on the way out? Like with the other TV, I'l trying to figure out if it is worth trying to get this quoted/repaired, but the cost-benefit analysis is a bit harder as I didn't pay so much for this one in the first place and it already has some other issues (geometry problems etc.) that may or may not improve with an overhaul.
Dochartaigh
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Re: Advice re: broadcast CRT repair

Post by Dochartaigh »

agrajag184 wrote:That's an interesting thought. Does anyone else here have a different feeling about recapping everything now vs waiting for more caps to fail and dealing with them then?
Recapping is always good (just as new parts installed in anything is good)... but it's WAY overblown and NOT a common issue with PVM/BVM's in my pretty large experience.

Out of the 120+ PVM and BVM's I've owned I can count on my fingers how many either had something wrong with them (that I couldn't fix geometry-wise through the service menu, or super simple no-soldering-required things like rotating the yoke 2º or whatnot), or needed to be recapped. Literally that super duper small percentage.

...Granted there was a batch or two of crappy composite 8" I didn't even bother testing but even if all of these were jacked-up I would still play those odds any day of the week that the capacitors in the vast majority of these are all working well still, even 20+ years later. Again, recapping is great, but I haven't had to do much of it at all on these and would only do if I REALLY enjoyed replacing caps and had a large stock on-hand already (and a good desoldering gun).
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matt
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Re: Advice re: broadcast CRT repair

Post by matt »

'80s and early '90s PVMs should absolutely be recapped. I've had 4 of them, and each one has had capacitor issues to some degree - some of which were pretty bad.
Dochartaigh
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Re: Advice re: broadcast CRT repair

Post by Dochartaigh »

matt wrote:'80s and early '90s PVMs should absolutely be recapped. I've had 4 of them, and each one has had capacitor issues to some degree - some of which were pretty bad.
Again, I'm NOT arguing that recapping isn't a good thing... but to reiterate my last point, I think I'm 9 for 11 (just did a quick count) from that exact era you mentioned. Probably statistically just a bit worse for wear than the majority I've had (mostly newer PVM-XX53/54's up to the BVM D and PVM L series), but still pretty darn bangin' for being that ancient. These are mostly Sony Cube's and XX30 and XX40 series. All have RGBS inputs. I take horrible pics of CRT's, but here's some I had handy, in various shapes of geometry tweakage - you can see the older RGB Trinitron dot logo or the older Cube/ProFeel lit-up buttons in a bunch of pics too showing these truly are some of the older models:

https://imgur.com/a/e8s0Xme

I threw in two bonus pics of my oldest pro monitors I've owned at the end of the album: JVC's from 1985 and 1987. Still look great for the technology of that time.
agrajag184
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Re: Advice re: broadcast CRT repair

Post by agrajag184 »

Interesting counterpoint. Going back a couple of posts, does anyone have any idea about the most likely cause of the intermittent intense whole-screen single-colour pulsing issue my PVM-1300E has been having? I'm hoping it is also just a recap issue or similar.
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matt
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Re: Advice re: broadcast CRT repair

Post by matt »

agrajag184 wrote:Interesting counterpoint. Going back a couple of posts, does anyone have any idea about the most likely cause of the intermittent intense whole-screen single-colour pulsing issue my PVM-1300E has been having? I'm hoping it is also just a recap issue or similar.
I don't think it would be a tube issue, sounds more like a problem with the RGB amp circuit. These are fairly simple and shouldn't be hard to trouble shoot. Bad pots are very common in these old monitors, that would be the first thing I'd check.

With a monitor that old, definitely open it up and check the capacitors. You're almost certain to find some bad ones. Sony was terrible at soldering back in those days too - you'll probably have to reflow some connections.
Dochartaigh wrote:Again, I'm NOT arguing that recapping isn't a good thing... but to reiterate my last point, I think I'm 9 for 11 (just did a quick count) from that exact era you mentioned. Probably statistically just a bit worse for wear than the majority I've had (mostly newer PVM-XX53/54's up to the BVM D and PVM L series), but still pretty darn bangin' for being that ancient. These are mostly Sony Cube's and XX30 and XX40 series. All have RGBS inputs. I take horrible pics of CRT's, but here's some I had handy, in various shapes of geometry tweakage - you can see the older RGB Trinitron dot logo or the older Cube/ProFeel lit-up buttons in a bunch of pics too showing these truly are some of the older models:
My situation is probably a little different from yours; I live in the tropics and the environment here is very harsh towards electronics.

With consumer TVs, I'd guess that at least half of the ones I find have at least one bad cap. The most common are the vertical pump-up capacitor and the filter caps on the cathode voltage line. It's absolutely not worth the trouble of doing a full recap on these TVs, but there are a handful of caps that I always check just to be safe and the effort is definitely worth it. Buying a good desoldering gun was one of the best investments I've made!
agrajag184
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Re: Advice re: broadcast CRT repair

Post by agrajag184 »

Hi again, lockdown in Sydney is finally over so I was able to get this CRT to a repair place so wanted to post an update.

The original issue with the horizontal deflection circuit was apparently a capacitor problem and is now fixed, and there was also a power supply issue that has been rectified. However, this now leaves me with a screen that is to my eye underscanning slightly. If I display the 240P test suite, the grid fills the screen, with all of the red boxes visible. The potentiometers for 'over-width' and 'over-height' are adjusted almost all of the way out, but whilst I can turn them the other way to make the image smaller, turning them the last few degrees doesn't make the overscan part of the image exceed the physical margins of the screen. On my other CRTs I generally try to get the red centre dots in the overscan area out to the edges of the screen rather than the whole boxes - so probably another 3-4% further out than it currently is. In particular this is nicer on the NES, where many games apparently had garbage graphics and colours in the overscan area. In the monitor's 'underscan mode' the same applies, but at most it fills about 80% of the screen regardless of how I adjust the 'width' or 'height' pots.

The reason for this post is that the guy that did the repairs said a few things that struck me as odd (and more generally seemed angry that I had brought him a CRT to work on despite paying him at his usual rate - not sure if he just wanted to get it done and me out of his hair). He advised that not being able to actually overscan an image is 'normal' for a broadcast CRT. He also advised that there was an issue with using a game console as the source as apparently when he connected a VCR or something he was able to adjust overscan further (however note he didn't have any calibration images available, just playing a video), and when he switched from that source over to the Sega Genesis clone I'd supplied him with to run the 240P suite, the same (analog) adjustments he was using inside the chassis stopped functioning. He asserted other sources sent additional protocols and control signals over analog cabling, which sounds impossible to me. Finally, he advised that this particular model (from about 2000 from what little I've found online) was a complex misture of analog and digital components ('the most complex CRT I've ever seen') and the digital part was likely limiting what the analog adjustments would do in specific situations.

Also interestingly, prior to him fixing the horizontal circuit (and advising he didn't touch the vertical one), I was able to overscan the vertical height quite a bit and had it set in the middle of the range - it now doesn't go as far out as before).

The monitor otherwise has disturbingly good geometry - honestly the only CRT I've ever seen that has LCD-like linearity. Thus I'm reluctant to get anyone to mess with the yoke (and don't want to do it myself as I don't know enough about electrical safety in CRTs to be comfortable doing this).

What are everyone's thoughts about what to do from here? Should I just put up with the slight underscanning and not risk ruining anotherwise perfect set? Should I take it to someone else? (not many other CRT repairers in Sydney, so it might be a pretty long trip).
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matt
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Re: Advice re: broadcast CRT repair

Post by matt »

He is correct in that many broadcast CRTs don't allow for as much overscan as consumer sets. Some of his other statements seem a little off though.

Try checking the B+ voltage. If it's low, the picture will be smaller than normal. You may be able to increase it slightly to get the image size where you want.

Don't touch the yoke. It has nothing to do with picture size. If your geometry, purity, and convergence are good, it means that the yoke is where it's supposed to be.
agrajag184
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Re: Advice re: broadcast CRT repair

Post by agrajag184 »

Good to know. Will leave it alone for now and see if the current underscan is bothersome in use or not. If so, will check on the B+ voltage next. Should that impact both horizontal and vertical size/deflection, or just horizontal?
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matt
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Re: Advice re: broadcast CRT repair

Post by matt »

Adjusting the B+ will affect overall image size. It can cause problems if it's set too high, though, so it shouldn't be indiscriminately cranked up.
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