1969 Baird 8724 - Single Standard CTV (A Rebuild)

Another thing that can make lines like that would be a dry joint on a low value non electrolytic capacitor.
The blue colour of the line is giving me a clue that it is likely to be in the blue drive or the output end of the decoder.
Provided the wire dressing was as original when the back was put back on and none of the ties have broken in the mean time then there must be a pulse sneaking out of the line scan circuit or even the coils if there are small capacitors there and getting onto the blue drive.

Provided the wire dressing was as original when the back was put back on

This set was rebuilt from an empty cabinet so that is not likely!

Chris gives the impression that the blue line has appeared some time after the rebuild.
The wiring could move if a tie has snapped so I do agree with the point about the wiring.
Both of these issues will need to be looked into.

Interestingly, the first thing that went through my mind was Barkhausen-Kurtz interference - a form of interference most commonly noted in early Band III receivers, particularly sets converted from Band I only use.

In those days it was caused in the Line Output valve and could be cured by fixing an ion trap magnet, with suitably bent pole pieces, over the valve - usually a PL81. I believe the PL81 was subsequently redesigned to shift the frequency up to the UHF area ...

However, BK interference appeared close to the centre of the screen and, as has been pointed out, only affects the blue channel in this case (but this could still be down to lead dressing). Is BK oscillation even possible in a solid state timebase ...?

What is the fault? well a vertical line that runs down the entire right-hand side

Did you ever get round to investigating this Chris?

Yes, I have an intermittent fault on my convergence board , its either a hairline crack or dodgy component, I checked for dry joints. I've been unable thus far to isolate it to either.

When I raise the board to its service position, the fault goes, when it is lowered, it comes back. In the lowered position when I push the board gently in various places it goes, it is not consistent where you push so no amount of research has yet revealed where the damn fault lies.

Last time I came across a fault like that it was a crack around one of the solder pads where a lead entered the circuit board. It was very hard to see.

Still not found the intermittent fault, here's a picture taken in the last couple of mins. Shows the fault is not present at the moment, I'm prodding around trying to make it appear then isolate. I think it might be heat related as it was present on start up then went.

Still not found the intermittent fault, here's a picture taken in the last couple of mins. Shows the fault is not present at the moment, I'm prodding around trying to make it appear then isolate. I think it might be heat related as it was present on start up then went.

Time for a can of freezer then...!

Hi Chris,

I have the remains of a Baird 8726 3000 chassis, not sure if the back is the same as yours. If it is your more then welcome to it and the metal frame work. While I'm at my mums I will have a look in the attic, must be over 8 years since it went up there.

Well done by the way on the set.

Marcus.

Hi Marcus,

Firstly welcome to the forum 

The 8726 back should be identical, it's the same set as the 8724, just in a posher frock. You can see it in the brochure on above on the blog.

If its is going spare I would gratefully accept your very kind offer, it certainly would be the icing on the cake. Let me know once you've checked, and we can take it from there.

Thanks for the kind comment on the set, it was a labour of love and my most cherished set.

P.s. Don't suppose you have the plastic surround for the CRT and its still intact? Mines quite damaged.

Hi Chris,

I got the set from a skip in a car park of a pub that had closed down in 2005. Sadly someone had chucked bricks at it and it was quite smashed up. I just took the back, tuner and the chassis. I know I still have the chassis frame work, minus all the boards. I found it at the front of the attic. Will have look later to see if the backs still there.

Regards,
Marcus.

Hi Chris,

Sadly this is all I can find. I will ask some of my old tv chums, just in-case I've given it them, and they don't need it. I've tried to post 2 pictures of what I have left size 100kb 800 by 600, but when I click "add the file" it just sits saying waiting for forum.radios-tv.co.uk then then times out?

Sorry I couldn't help.

Marcus.

Hi Marcus,

Never mind, the Korting back I have fits OK and all I have to do to finish is find a large flat fibre board to run across the bottom section. Thanks for thinking of me though 

Odd re the photos, they should load up OK 100 KB is well within the files size limit, no restriction on dimension so 800×600 is fine.

I take it you clicked on Upload attachment - Choose File

select the file from the computer and click open

That should load them, unless they are over 120 KB where they will be rejected.