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CTV Co Op (Bush T24E) no video fault

 
19Seventie
(@19seventie)
Trusted V-Ratter Registered
Posts: 95

 

Hi all

I've recently seen mention of the T24E chassis and Co-op badged sets on this forum so I thought why not bring the two together with my Co-op badged T24E.

It's been some time since I looked at the set as I think I was in way over my head with it at first but now I'm a little more clued up I think I can return to this set. 

The set powers up and will display a raster but it's totally blank when tuned in, though I get sound. If I detune there are signs of the set trying to give snow on screen but it's very weak looking as seen below. I was just wondering if anyone here was familiar with the fault on this set and could point me in the right direction? I did once get a "picture" of sorts on screen from a TV guide but that's the best it's ever been

Thanks
'77

Cyan
idk
TV guide
front
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Topic starter Posted : 05/07/2022 1:33 am
crustytv
(@crustytv)
Vrat Founder Admin
Posts: 11044
Posted by: @19seventie

The set powers up and will display a raster but it's totally blank when tuned in, though I get sound.

Blank raster, but sound, classic symptom of a vision fault, and need to look at the i.f. panel for the source. Have a look at the service manual, it shouldn't be too hard to track down the culprit.

If you've not got the manual, let me know, and I will get it scanned for you.

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Posted : 05/07/2022 7:45 am
crustytv
(@crustytv)
Vrat Founder Admin
Posts: 11044

Here's a snippet of the relevant part of the circuit, and a datasheet for the Vision Detector I.C. TA7611AP.

bt24e
TA7611AP
Posted by: @19seventie

I was just wondering if anyone here was familiar with the fault on this set and could point me in the right direction?

See what voltages you have on the TA7611AP, that may give some clues, or at least rule it in or out of suspicion.

If that is OK, then it's down to the vision i.f. stages below, checking voltages on TR201, TR202, TR203, TR204 & TR205.

Might help if you have a scope and pattern gen, to inject a colourbar, but if not a meter will suffice. From the cct you can see the expected waveforms and voltages are in red, compare them to what you have. I've highlighted in green where the IC and 5 transistors are located. The board silk screen has the IC pins and transistors b,e,c marked, so it should be straightforward to know where you are.

t24Visionchk

p.s.

To get the best view of the uploaded forum image of the cct, click on image, then right-click, "open image in new tab", will open the image to a better size. I have uploaded the full service manual in the data library.

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Posted : 05/07/2022 11:02 am
Jamie
(@jskinner97)
Noble V-Ratter Registered
Posts: 1601

They're a VERY primitive basic set. I should know, I've got the Bush/Rank branded version. I tell no lie when I say it has been in full time (6hr a day plus) use in my lounge (with Youview/Netflix etc) for 12 years!

They perform rather well, although colour isn't as "strong" as on Philips sets of the era for instance, but the Toshiba tube in mine still has a spectacular amount of brightness left. In the 12 years it's been in continuous use it's only ever needed a single resistor.  - and of course i've no idea it's life before I got hold of it. It had a PAT test sticker on from 2007 and I imagine it was a rental set once.  Not bad for 42 years old. I will happily use it until the day it dies. 

Obviously my phone can't capture the image well! 

tv
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Posted : 05/07/2022 6:15 pm
19Seventie
(@19seventie)
Trusted V-Ratter Registered
Posts: 95

Hi all

I've not forgotten this thread, honest! It's been really busy this week so I've not had much chance to drop in, and certainly not to reply!

Chris, Luckily I have a circuit diagram which I was kindly sent once but unfortunately at the time could make no sense of it, or any other diagram for that matter

The Pin out diagram of the TA7611AP IC will be very handy, I'll definitely use that. I did suspect an IC but that was me blindly guessing. Thanks for marking the transistors and IC out too, much appreciated. I'll have to pull the set out and try it. I can feed it with some colour bars too.

Jamie, Thats a lot of hours! How well has the tube fared as in how much have emissions dropped roughly, do you know? It's something I'm always so cautious about when using sets, to not use them too much to preserve their emissions. Would that resistor be the one near the LOPT by any chance? R309 comes to mind but I doubt that's right! Just as a bit of fun, I have the exact same VCR and set top box as you too! What are the odds of that?

Thanks both, will let you know how I get on with the readings!
'77

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Topic starter Posted : 10/07/2022 8:41 pm