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Old 30th Sep 2022, 5:49 pm   #1
Retrorepair
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Default Sony KV-A2942U very soft focus in middle of screen

Hi all,

I've gone back to consumer Trinitrons, the PVMs were nice but too small for me

The issue I have with this one is the focus. The edges are nice and sharp, but the middle of the screen is very soft, like the very center top to bottom, getting sharper towards the left and right.

Adjusting the focus doesn't help, though making the screen very dark does (but it's basically unusable at this point).

I see there's a service bulletin to replace an LM393 if this is the case, but I believe this is only for AE2 sets with dynamic focus which I don't think this one has.

Is there a known fault with these that can cause this? Maybe a cap in the PSU section or something?
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Old 30th Sep 2022, 6:36 pm   #2
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Adjusting the focus doesn't help, but what does it do instead?

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Old 30th Sep 2022, 9:46 pm   #3
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Default Re: Sony KV-A2942U very soft focus in middle of screen

It focusses the left and right, the middle just get less and more blurry. When the outside is sharp, the middle gets as sharp as gets.. which is still very much out of focus
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Old 30th Sep 2022, 10:13 pm   #4
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Sounds to me like the mask is "bent ". A decent knock can sometimes cause it to sag in the centre.

Joe
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Old 30th Sep 2022, 11:54 pm   #5
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Default Re: Sony KV-A2942U very soft focus in middle of screen

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Originally Posted by joebog1 View Post
Sounds to me like the mask is "bent ". A decent knock can sometimes cause it to sag in the centre.

Joe
I'm not so sure Joe, a bent shadowmask would cause purity problems which the OP hasn't said happens.
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Old 1st Oct 2022, 5:37 am   #6
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Default Re: Sony KV-A2942U very soft focus in middle of screen

I didn't even know that was possible! But no, no purity problems beyond a little bit in the corners consistent with just about any consumer trinitron I've seen.
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Old 1st Oct 2022, 8:46 am   #7
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Default Re: Sony KV-A2942U very soft focus in middle of screen

I'm wondering if Joe might be right here. Do you know the history of the TV?

Do check if it does have dynamic focusing as many of the big ones did. We can hope!
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Old 1st Oct 2022, 8:58 am   #8
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Quote:
Originally Posted by Michael Maurice View Post
Quote:
Originally Posted by joebog1 View Post
Sounds to me like the mask is "bent ". A decent knock can sometimes cause it to sag in the centre.

Joe
I'm not so sure Joe, a bent shadowmask would cause purity problems which the OP hasn't said happens.
This is a Triniton with different construction and doesn't have a shadow mask, poor focus can be caused by a bent aperture grille. Have seen this while working with Sony.
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Old 1st Oct 2022, 1:49 pm   #9
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Would it focus well at low brightness though? I guess maybe since the beam would have less spread?

Attached is the best I can get it anyway. I've a feeling there's some yoke shuffling in my future too, top and bottom convergence on the left is pretty off.
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Old 1st Oct 2022, 2:10 pm   #10
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Quote:
Originally Posted by Welsh Anorak View Post
I'm wondering if Joe might be right here. Do you know the history of the TV?

Do check if it does have dynamic focusing as many of the big ones did. We can hope!
No idea, previous owner likely never even noticed. It's my curse I suppose seeing these things.

I think AE2 chassis of this generation had a D1 board for that, this doesn't have one sadly. It is filthy inside so could possibly have a few caps that have leaked. I actually think it's spend some time in a shed or garage at some point, it does smell a bit rodent uriny, so a good clean at least I think is in order.

I do somewhat suspect the flyback isn't well either, turning it on from cold you can hear some pretty distinct arcing coming from that area, sort of like a fizzing sound accompanied by what I can only describe as "high voltage smell" if that makes any sense at all! It does settle down after a bit, the focus doesn't change in this transition though.
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Old 1st Oct 2022, 2:57 pm   #11
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Default Re: Sony KV-A2942U very soft focus in middle of screen

No offence, but I wonder if you're just being a tad too critical? You say you're used to small-screen PVMs which have nice sharp pictures.

Now you've got a high-mileage large-screen domestic TV without dynamic focus, which was added in later versions.

I remember being in a studio where the editor did his work on a PVM. Then to check it for broadcast he routed it to a domestic Sony TV. It looked terrible to me after we'd spent the day looking at the monitor, but it gave a good domestic picture.

You could always save up for a large screen BVM....
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Old 1st Oct 2022, 3:16 pm   #12
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Default Re: Sony KV-A2942U very soft focus in middle of screen

I know what you're getting at, but I've also got a KV-X2942U that has a beautiful picture. Again, there's the usual convergence issues in a couple of corners but the focus is much sharper than this. I've not had many AE2s though, maybe they were just like this?
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Old 1st Oct 2022, 3:50 pm   #13
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Quote:
Originally Posted by Welsh Anorak View Post
No offence, but I wonder if you're just being a tad too critical? You say you're used to small-screen PVMs which have nice sharp pictures.

Now you've got a high-mileage large-screen domestic TV without dynamic focus, which was added in later versions.

I remember being in a studio where the editor did his work on a PVM. Then to check it for broadcast he routed it to a domestic Sony TV. It looked terrible to me after we'd spent the day looking at the monitor, but it gave a good domestic picture.

You could always save up for a large screen BVM....
While I've got you, I just wanted to see if the attached looks normal? I turned the H-STAT all the way to separate the RGB and I'd hoped I'd find using the rings easier. Should the beam landing be so spread out like that as it gets to the edges? I feel like this may be part of the issue, the landing in the centre is almost on top of each other when the H-STAT is properly adjusted which may explain my symptom?
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Old 1st Oct 2022, 3:55 pm   #14
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Seems like the vertical alignment is a bit weird too, it'sperfect in the middle but alternately splays out top and bottom. Or should I expect this maxing out the H-STAT?
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Old 2nd Oct 2022, 7:36 am   #15
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Hi.
You say the set is filthy. Is this from fag smoke and all sticky?
Believe it or not that could be your problem, it can be cured but I'll get shot down again for suggesting this. The whole board needs a wash with detergent and very hot water, with soft water or distilled into the bargain, rinsing and the drying process is critical and will need a good couple of days to complete (an air line is best initially) then a hairdryer giving around 60 to 70c of warm air, then a good few hours around 50c,i can guarantee it will work if done correctly. The arcing is quite possibly tracking from nicotine.
I'd also say the set is high mileage and if the grime is not what I suggest then I doubt you'll improve the set. Also setting scan coil positioning and magnet alignment on a Triniton has to be done in a set order or you'll never get it right.
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Last edited by murphyv310; 2nd Oct 2022 at 7:43 am.
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Old 2nd Oct 2022, 9:44 am   #16
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Hi

The screen shot explains why the centre "focus" is poor whilst the edge seems fine.

It is because the horizontal tilt and amplitude dynamic convergence requires setting up.

From the screen shot, static convergence looks fine. Any edge mis-convergence can be corrected by the permalloy strips.
-
What ever you do, you MUST read the service manual to get a hang of the dynamic //static convergence in a domestic Sony TV. It isn't difficult but without the instructions in front of you, you will end up wishing you had left well alone.

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Old 2nd Oct 2022, 12:00 pm   #17
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Thanks guys. I've cleaned several chassis this way in the past, they come up like new. I do always make sure I seal the anode cap and top of the flyback to avoid any ingress. I wouldn't mind betting a cap or two will have spilled their guts too looking at it.

The Sony manual does outline the process, though I can't for the life of me work out some of the language or illustrations. I scoured youtube but no one seems to have documented the process which I find odd. Maybe I need the services of @Welsh Anorak for this bit?
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Old 2nd Oct 2022, 1:08 pm   #18
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Default Re: Sony KV-A2942U very soft focus in middle of screen

I used to train the apprentices and one of the tasks was the Triniton purity and convergence when working for Sony. The last time though was 1996 so I'm a bit rusty, I'm sure it would all come back after reading the manual.... Assuming I had one!

I'm sure this is an AE2B chassis but with no dynamic convergence.
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Old 2nd Oct 2022, 1:14 pm   #19
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Default Re: Sony KV-A2942U very soft focus in middle of screen

https://www.manualslib.com/download/...Kv-A2941a.html

There's one

I think if I had a little bit of guidance, I could probably do it. I've got most of it but some of what it describes doesn't make sense to me.
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Old 2nd Oct 2022, 3:57 pm   #20
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Default Re: Sony KV-A2942U very soft focus in middle of screen

Hi.
Where are you getting stuck with the instructions?
It's important to basically start from scratch, remove the ferroxcube magnets and any little round magnets stuck to the cone in corners etc. Follow the instructions, use a dot pattern at low brightness and make sure centre focus is spot on. Think of it you are fitting a new CRT. Trying to correct existing convergence isn't easy so basically start from scratch.
Come back if you have problems. Remember if you cannot get this correct then is possible the CRT is at fault, doming can occur, this is caused by heat in the aperture grille due to high beam current and is more of an issue with large screen Triniton CRTs this can eventually cause permanent damage that effects purity and convergence.
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