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Bush/Rank - Toshiba T24 chassis??

 
Jamie
(@jskinner97)
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Posts: 1518

Hi all, I’ve been using my trusty Bush/Rank tv now for nearly 10 years every single day! With only one breakdown it’s been fabulous, which is surprising as it’s inherently very basic with respect to component count. I believe it uses the Toshiba T24 chassis, although there are some variations. 

Anyhow, it’s been working fine for years using a VCR as an RF Modulator for my freeview box, recently I upgraded to Virgin Media and as with most things these days I require HDMI. I bought a HDMI to scart converter which works very well, it downscales to NTSC or PAL. However sadly this TV only produced a black and white picture with it!!

I’ve  tried a  different RF Mod, RF Channel, HDMI Source, SCART Lead etc and it still produces the same problem.

However, it works fine on my similarly aged 1981 Pye (Philips) KT3. 

I noticed tuning the Bush out slightly produces the colour, so the problem must lie with the Bush TV! I’ve also tried AFC and it makes no difference.

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Can anyone shed any light? Preferably RGB light lol, cheers. 

 

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Topic starter Posted : 02/06/2019 8:27 am
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Nuvistor
(@nuvistor)
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Presume it still works with the free view box and VCR correctly.

If the old system works ok it suggests the HDMI converter is  outputting a signal that is not true specification, the Philips handles it ok but the Bush must be more strict or the Bush is on the edge of working conditions and the two don’t mix.

If you have a scope it would be worth checking the chroma signal after the video detector to see if you can determine what is occurring.

The T24 will probably have a way of overriding the colour killer, see what the picture is like with that overridden.

 

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Posted : 02/06/2019 9:51 am
PYE625
(@pye625)
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Hard to say for certain if your RBM is actually faulty Jamie....

I have trouble with my Sony KV1320 (not strictly a true PAL set I know) being rather fussy about the video source, the hue being way out of adjustment with some sources, but it is perfect with a Sony DVD player on a cheap UHF modulator. A Philips PM5515 pattern generator is fine too, so I guess it could be a case of some set's although working ok to their spec, not liking the processing done within some converters.

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Posted : 02/06/2019 10:32 am
Terry
(@terrykc)
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Check the burst timing with respect to the burst gate timing. 

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Posted : 02/06/2019 11:41 am
Jamie
(@jskinner97)
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Posts: 1518

Thanks for your help guys, after speaking to roger locally he advised me to adjust the chroma pot, which seems to have cured it indeed!

can anyway explain what the chroma pot actually adjusts? Am I right in thinking it adjusts the frequency deviation between the sound and video carrier?

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Topic starter Posted : 02/06/2019 3:06 pm
PYE625
(@pye625)
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Well it is a Toshiba, so I was right to talk a load of Tosh earlier. ? 

Glad you got it working ? 

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Posted : 02/06/2019 4:32 pm
Nuvistor
(@nuvistor)
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Chroma pot, I would need to see the circuit to try and suggest an answer. Various possibilities come to mind.

Wouldn’t have thought it is the frequency deviation between sound and videos carrier, that is set at the transmitter.

 

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Posted : 02/06/2019 6:04 pm