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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 10th May 2010, 3:54 pm   #501
PJL
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Default Re: Pye v4

Chris, as I also know nothing about 405 TV's (but I have learnt alot form you!) this is my laymans thinking...

The video is showing some smearing, after a burst of white there is a smear of black which should not be there. The bends in the verticals also follow the pattern of the image and if you look carefully, you will see the vertical distortion appears at the beginning of the line. This implies the sync pulse is also being smeared.

You will find an article here http://graffiti.virgin.net/ljmayes.mal/var/tvsync.htm. It's 625 interlaced but at least shows the sync pulse and back/front porch.

So we are most likely looking at a problem in the RF or video amplifier.
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Old 10th May 2010, 3:59 pm   #502
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Default Re: Pye v4

Peter,

Spooky I was reading about the back and front porch this afternoon in Spreadburys book.

The video amplifier is what I have been looking at (V8 Ef80) and that is where I think the sync decoup capacitor John W is refering to should be.I think I have changed it already. I have changed most caps except all the low pF's and the flat round ceramics in the RF and other areas, I thought these were pretty stable caps.
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Old 10th May 2010, 4:13 pm   #503
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Default Re: Pye v4

Peter I would be interested in your suggestions as where to look as on two ocassions you have been spot on so please offer any advice.

I don't want to incurr the wrath of John & Trevor, as they will go nuts when they find out that the line setup still has not be done and might be the route of this issue and I have not figured out the sync decoup cap (although I think I have changed it)

I have switched on and observed the following:-

Test card appears but is squshed and quite dark, as the set warms up the test card expands and becomes brighter and the vertical/horizontal lines are straight, the centre circle is squashed. Eventually the test card just about fills the screen and is resolved nicely. Then the definition decreases and it looks slightly smeared as if capacitance has been added to video circuit as described in fig 172 page 26 of Sreadbury, although not as severe.

This all takes place within 8mins

pictures 1-5 show the progression.
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Old 10th May 2010, 4:13 pm   #504
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Default Re: Pye v4

I'd agree Chris, the linearity isn't bad.
To be honest, I don't think I've ever seen a V4/VT4 with really good horizontal linearity and I've attached a snap of mine which was at an early stage of resuscitation. The line linearity coil on my set is quite badly fried and isn't adjustable.. perhaps that's the way they all go (?). I haven't done any work on mine since this photo was taken, so I don't know.
The black level gated AGC acts only on one valve, V4, and unlike later sets it has quite a restricted range, meaning that the sensitivity control must be set to put the signal level at this valve within the range that can be handled by the AGC system.
If any stage of the set in front of this one goes into overload there's nothing the contrast control can do about it, hence the separate sensitivity adjustment at the front end.
As has been mentioned, the line sync has to be set up well for the AGC to work properly.
I'd say Well Done!

Pete

PS Before I get shot to pieces, I'm not saying a V4 with good linearity doesn't exist, only that I've never seen one !!
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Old 10th May 2010, 4:16 pm   #505
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Default Re: Pye v4

It's the blind leading the blind...

The kind of fault I think we are looking for is something like a valve going into grid current or one of your new diodes being too slow. I guess a decoupling problem is another possibility. The tricky bit is how to find it without a scope?

Disconnect MR1 and try again.

PS: Another interesting feature is the overshoot is occuring on both black to white and white to black.

Last edited by PJL; 10th May 2010 at 4:29 pm.
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Old 10th May 2010, 4:32 pm   #506
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Default Re: Pye v4

I think before I do anything else I have to do this line setup as clearly the AGC is paramount on this set. Has anyone got the PYE V4 manual or have knowledge of the setup procedure.
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Old 10th May 2010, 4:40 pm   #507
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Default Re: Pye v4

Hi Dangerman,

I drool at the quality of your picture....................that's the sort of grid I should have and I'm aiming for

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Old 10th May 2010, 5:08 pm   #508
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Default Re: Pye v4

I can see how it samples but can't see any adjustment instructions?

Anyhow my PS above suggests it is not grid current as it would be asymetric and not effect both black to grey and white to grey.

I guess you haven't done any electrolytics? C33 needs to be done.
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Old 10th May 2010, 5:10 pm   #509
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Default Re: Pye v4

Correct well almost, I replaced C98 that's all.

I only have 22uF's or 32uf's near to that, guess the 32's will suffice
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Old 10th May 2010, 5:35 pm   #510
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Default Re: Pye v4

C33 is 2uf. What's the largest non-electrolytic you have? It certainly needs replacing before we can draw any conclusions on the video.

There is also a distinct lack of decoupling on the HT line which supplies the video amp.
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Old 10th May 2010, 5:45 pm   #511
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Default Re: Pye v4

Stupid me,,,, I was looking at the wrong cap. Not to worry I have a range of electrolytics ,nearest to that is a 3.3 or a 4.7
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Old 10th May 2010, 6:26 pm   #512
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3.3 is fine.
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Old 10th May 2010, 6:27 pm   #513
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Default Re: Pye v4

The sync coupling capacitor [not decoupling] is C74 .1uf connected to pin 2 V19 EF80. J.
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Old 10th May 2010, 6:28 pm   #514
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Default Re: Pye v4

Hi
I will scan the manual for you later on after tea and post it here.
Is there any chance you could take or ask an engineer to pop in and go over it with you, of course posting progress here?

Please don't think I am in anyway angry at you, I am a terrible joker but often people get the wrong end of the stick.

You were asking about apprentices, well usually in two months you really hadn't learned a lot unless you were "in to it" beforehand. Normally you would wash the bosses car, clean the lavvy's, put up aerials, go for the tea stuff and help with deliveries, but this made you a better person.
When you did get on the bench you worked with all sorts from hopeless engineers to genius's, I was very lucky with the people I worked with and enjoyed my apprenticeship although I still got plenty of "clips round the earhole" but i would never give them "lip" back as I had great respect for them, because of this I finished my apprenticeship with Distinction passes on the City & Guilds Radio & TV Technicians course.

What you are trying to do on your own and through this forum is very difficult, why I say this is you have no hands on help, when you ask a question there will be numerous answers some correct, some wrong and some confusing. You have to take photos and type on a keyboard, but with a qualified person guiding you he will tell you what is happening in a circuit, and what would be required to cure any fault seen.
Please everyone I am not downcrying the forun in anyway, but as this is a complex set Chris really needs a "buddy" beside him, you cannot run before you walk.
If it was me I would have gradually worked up to a V4 and done some Bush's, Regentone's and straightforward sets then move up to the V4.

I will post the diagram later, is tea time!
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Old 10th May 2010, 6:35 pm   #515
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Default Re: Pye v4

If you're scanning the V4/VT4 manual I suspect it will be a bit big to attach to the forum. I would appreciate a copy too, for when I finally get round to the ones I've had sitting in my loft for years. Don't even know if they are V4 or VT4. I wonder if Jon Evans would be willing to host it on his website?
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Old 10th May 2010, 6:39 pm   #516
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Default Re: Pye v4

John
yup already done C74

Trevor,

Don't worry, when this is over I'm going back to Bushville and making a start on my TV22, I may even stop after that, 4 Tv's is probably a good place to stop anyway before it gets out of hand

PJL
I'm changing C33 as discussed will report back.

Chris
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Old 10th May 2010, 6:45 pm   #517
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Default Re: Pye v4

I'd appreciate a copy too Trevor.

I must agree that tackling the V4/VT4 with limited experience of battling with 405 telly repair is certainly jumping in at the very deep end,though looking back you'll see it as a great experience.

Hugh
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Old 10th May 2010, 8:01 pm   #518
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Default Re: Pye v4

I think we can turn a blind eye to this for a little while

Ok, time's up!
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Old 10th May 2010, 8:06 pm   #519
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Default Re: Pye v4

Thanks Trevor

PJL
after C33 change
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Old 10th May 2010, 8:11 pm   #520
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Default Re: Pye v4

Hi.
Is R41 4.7meg within 20%? and R43/44 also has C37 been changed/checked?
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