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Forum 141

KB PVP20

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Terrykc
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Posted by: @sideband

Also beware the vision interference limiter which may be incorrectly set. If this is advanced too far, it can make the whites appear grey and silvery just like a duff tube.

... as I said earlier ...!

Better still, there is a link shown between L22 and the cathode of V6a - just remove it!

When all else fails, read the instructions

 
Posted : 24/09/2014 3:00 pm
Anonymous
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I have done a lot more in the way of capacitor changing on the TV. Got the picture back and it is quite good.
There were problems with the height, I had to have it full on, it improved after changing C57 C61 C43.
The picture is still a bit wishy washy, I guess that is the tube, but it is watchable in a darkened room, and it is a bit to the left, but I can live with that.
Thats it I think, its about all I can do, other than boost the tube, and that is probably not worth taking the risk.
Thanks Everyone
Mike

 
Posted : 13/10/2014 9:21 pm
Anonymous
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A further slight improvement, I had a go at changing the focus settings and found it was better on pin 9.

There are 2 more wax capacitors to change, C49 & C80, I have run out of spare .1 and .047 caps.
Would it be expected that these capacitors will make much difference to the picture quality?
They can both be seen on this image. download/file.php?id=18967&mode=view

In order to get the most stable picture with the horizontal hold the picture is to the left, if I centre the picture then the edges of vertical lines start to go wonky.
It looks from the test card that the image is slightly stretched out on the left.
I would appreciate some advice on how to get the circle round or to shift it to the right, and maybe the width may need reducing slightly now.

Thanks

Mike

 
Posted : 14/10/2014 11:42 am
Anonymous
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Hi
The left side of the picture is a little stretched, I would appreciate some advice on how to get the circle "round" or to shift it to the right, and maybe the width may need reducing slightly now.

 
Posted : 15/10/2014 8:14 am
Terrykc
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Does this set have a line linearity sleeve under the scan coils?

It consists of a shorted turn made from copper foil and glued onto a paper sleeve which fits around the CRT neck under the scan coils. By moving it backwards and forwards, it is used to set both width and linearity, although predominately the latter. It should have a little plastic 'handle' glued to the end closest to the CRT base but they often become detached, usually because the sleeve stops sliding freely after a time ...

To adjust, slacken the scan coil clamp and pull the sleeve back as far as it will go. Now slide it slowly forward until the linearity is at its optimum, then re-tighten the scan coil clamp. Note that is the sleeve is pushed too far forward, it can cause the scan coils to run at an increased temperature, so don't overdo it!

When all else fails, read the instructions

 
Posted : 16/10/2014 7:41 pm
Anonymous
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Thanks for your reply, not sure if you mean the ring around the neck near the end or the other clamp thing up close to the scan coils.
Perhaps you could point for me.

 
Forum 147

 

 
Posted : 16/10/2014 10:14 pm
Terrykc
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Ah! Neither, (Sorry, there's no data in the library on this set, so I was working in the dark ...)

This set is a bit too old for the linearity sleeve trick!

The ring near the base is, presumably, an ion trap magnet (of a type completely alien to me!) and the 'clamp thing' is the picture shift magnet assembly.

Hopefully you'll find linearity and width controls in the line output stage.

When all else fails, read the instructions

 
Posted : 17/10/2014 4:19 pm
Anonymous
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The ring near the base dosent "feel" magnetic with a screwdriver.

 
Posted : 17/10/2014 4:58 pm
crustytv
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Posted by: @terrykc

Ah! Neither, (Sorry, there's no data in the library on this set, so I was working in the dark ...)

Yes there is, it's been there for about two years as I had one of these sets

KB_PVP20_Trader 1016.67 KB
Kb_qvp20_ser_man 2.21 MB

As you can see, there was a Trader sheet and the KB service manual. The only difference between the PVP and OVP is the vabinet construction. The PVP uses a Card type cabinet, the QVP a glass-fibre cabinet.

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Posted : 17/10/2014 5:15 pm
Terrykc
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Posted by: @crustytv

Yes there is, it's been there for about two years as I had one of these sets

KB_PVP20_Trader 1016.67 KB
Kb_qvp20_ser_man 2.21 MB

Oops!

I accidentally clicked on F-J instead of K-O ...!  ☹️

I saw several ITT-KB sets but not the PVP20 and so ... 

Grovelling apologies, Chris.

However, the two are not the same. The QVP20 uses a different CRT and shows a width sleeve as part of the scan coil assembly whereas the the PVP20 has three width plug selectable settings on the LOPT ...

When all else fails, read the instructions

 
Posted : 18/10/2014 12:10 am
Terrykc
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Posted by: @anonymous

The ring near the base dosent "feel" magnetic with a screwdriver.

Data on the Brimar C17SM doesn't mention an ion trap magnet but the Philips/Mullard data for the equivalent AW43-80 definitely does!

Assuming it is some type of ion trap magnet with an enclosed field, as everything looks ok from the pictures I would suggest you avoid disturbing its position!

When all else fails, read the instructions

 
Posted : 18/10/2014 12:20 am
Anonymous
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I just wondered if there was a simple way to squash the leff side of the screen over to the centre a little. But as it is not too bad I think I will leave it alone now apart from changing the last 2 caps when they arrive.

 
Posted : 18/10/2014 10:02 am
Terrykc
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I just wondered if there was a simple way to squash the leff side of the screen over to the centre a little ...

There is!

I missed this earlier but this set does have a shorted turn linearity sleeve!

As I covered the adjustment of this in a previous post, I wont repeat myself ...

I found this in a much earlier post:

... In order to get the most stable picture with the horizontal hold the picture is to the left, if I centre the picture then the edges of vertical lines start to go wonky ...

Is this still happening, because it shouldn't!

Also note that the horizontal hold control should never be used to centre the picture!

When all else fails, read the instructions

 
Posted : 18/10/2014 10:50 pm
Anonymous
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Thanks for the information, so the linearity coils are actually fixed to the sleeve the scan coils are mounted to.
I dont fancy touching that as it all looks bolted up, and I fear making a quite minor imperfection worse.

Yes the picture is still to the left slightly, in order to get the best lock on the horizontal hold.

I was wondering about giving the ring around the neck a gentle tap, but it looks like it may be a ferrite material and I am worried about that cracking and making matters worse.

 
Posted : 19/10/2014 8:37 am
Terrykc
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... so the linearity coils are actually fixed to the sleeve the scan coils are mounted to ...

No, although it sometimes seems that way!

The scan coils are completely separate from the linearity sleeve, which consists of copper foil coils on a sheet of thick paper.

To adjust them, first release the scan coil clamp. You should be able to see the sleeve protruding from the rear of the coils, even if the plastic 'handle' is missing. You may need to release the picture shift assembly to get to it easily.

Over time, the sleeve may have got loosely bonded to the scan coils or the tube - or both! Hold the sleeve whilst moving the scan coils slightly to ensure they are free then move the sleeve backwards towards the tube base. If you need to twist the sleeve to free it from the CRT neck, make sure it is rotated back to the original position. The 'handle' has a projection which engages with a slot in the scan coil housing to make this easy but you can use a pen to make a datum mark on the sleeve before moving it if the 'handle' is detached.

Ensure the scan coils are fully forward, then gradually push the sleeve forward under the coils whilst observing the linearity - ignore width changes during this process. Tighten everything up again, re-centre the picture, then adjust height and width - if necessary - for optimum.

Don't interfere with that ring near the base!

When all else fails, read the instructions

 
Posted : 19/10/2014 12:12 pm
crustytv
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If it helps this is what the lin sleeve looks like.

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Posted : 19/10/2014 12:20 pm
Terrykc
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Thanks, Chris! I was thinking that I might attempt to draw one but those pictures are much better than I could ever dream of!

The only thing that isn't clear from the pictures is the location (anti-rotation) lug which should follow the gap between start and finish of the rolled up sleeve ...

When all else fails, read the instructions

 
Posted : 19/10/2014 12:27 pm
crustytv
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.

CrustyTV Television Shop: Take a virtual tour
Crusty's TV/VCR Collection: View my collection
Crustys Youtube Channel: My stuff
Crusty's 70s Lounge: Take a peek

 
Posted : 19/10/2014 12:42 pm
Terrykc
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That's the bit I was trying to describe - thanks Chris.

I've highlighted it for clarity. In this case it is 180° from the start/finish gap, which makes no difference.

When all else fails, read the instructions

 
Posted : 19/10/2014 2:02 pm
Anonymous
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I have had a go at the "non destructive tube rejuvenation" with this KB set, with some good results..
see

https://www.radios-tv.co.uk/community/black-white-tvs/non-destructive-tube-reactivation-updated/#post-100076

 
Posted : 22/10/2014 4:57 pm
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