Toshiba 3787db OSD issue

[roystonb]

Hi all, I've got a 37" Toshiba which seems to have no sync for the osd
Teletext is fine, but Teletext mix has the same problem : flickering/rolling osd to the point of being unusable!

I've attached some photos to help explain what I mean, if anyone has any ideas I'd really appreciate them!

[zeno]

Looking at the model ## I assume this is not a US sold set. In the
US it is probably a 35## model, actual screen size ( 35").
Anyways most problems like this are bad electrolytic caps. Usually
small surface mounts in the PIP or video in general. This type of problem
can make a tech run like hell !
When new you could buy main boards & sub assemblies until they were gone.
After that if in warranty the set was junked & replaced.
So sorry I cant give a simple solution but maybe others can help.

good luck
73 Zeno
LFOD !

[roystonb]

Thanks Zeno!

I was wondering if it could be a dry solder joint somewhere, as it was working before it was moved!

If I call up teletext and then change volume via the remote, the OSD appears fine - its only when overlaying text or OSD over the source image, all inputs and tuner as well.

I have the service manual, but I'm struggling to find the circuit responsible for "mixing" text over image.
Happy to share the manual if it will help

Edit: Yes its a UK 37" model, a bit of a holy grail over here as it was the largest 4:3 CRT available over here so would like to get it fixed if possible.. there are very few CRT techs still working these days!

[zeno]

OSD can be generated in the micro or jungle IC. The data was stored in an
E-prom usually. Zenith was the only teletext builder I know of here in the colonies. It was in digitally processed NTSC sets ( ITT chip set ). Cant help there as all the digital stuff was on a module w/ plug in IC's so that would be swapped out.
Looking for cold joints & unseated connectors a good start. Especially watch
the plug / sockets of sub boards & input jack packs. And always watch for bad
hook up cables !
Also look up the data sheets on the jungle IC that can give you a good
idea of where the I/O's are & more
Hope you get her going again. Let us know how you do.

Cheers
Zeno
LFOD !

[roystonb]

I've uploaded a video to better show the problem:

https://vimeo.com/791901404

A couple of updates, the jungle IC is a TB1230N, also I've brought up an inbuilt test screen from the service menu, and that shows the same problem, whereas OSD over teletext doesn't

I've got the datasheet for it, but it doesnt seem to explain how the OSD is overlaid over the source RGB signal... is blanking involved here?

Someone who used to repair CRTs is coming to take a look later this week hopefully, worst case I'll be able to get some photos if he struggles to fix it!