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Fitting Video/RGB inputs to Thorn TX10/TX100 chassis

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Red_to_Black
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The actual Article description is as follows:

"Scart connector, Adding

Pg 866 October 1991

An interface circuit that enables a SCART connector to be added to sets employing common IF, sound and PAL decoder chips"

By the description, it sounds like a general article to me rather than for any specific set.

As already said I don't have the actual article, just the index, so cannot see what actual advice and guidance is given

Thorn, like many makers had their own design "quirkiness", I know that links had to be cut on the TX100, on the TX10 I only have a basic chassis diagram from the early version, and this may pre-date the scart kit.

Although a reference is made to AV on this early diagram, but this is only with regard to the sync chip, I have a feeling "AV" in this context refers to the "video Channel" to cater for VCRs and altering the time constant, and for also Thorns own DIN socket/s arrangement which also routed the remote control commands for their own range of VCRs through the TV IR receiver when both DIN connections were used with certain Ferguson/Thorn VCRs of the same era.

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Posted : 16/12/2014 12:24 am
Till Eulenspiegel
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In the 1980s I did have a number of 22B5 "Professional Series" sets on rental, a very popular set with customers. Pseudo stereo sound and of course the SCART socket. Separate matching loudspeakers which could be placed alongside the set or positioned elsewhere for the perfect stereo effect. I still have a pair of speakers rescued from a written off set. Ex-rental sets had to be smashed up in those times. Tax reasons. The fact I bought these sets direct from TCE means there might be a manual supplement somewhere in the shop.
When I find one of the write-off lists I'll post one on the forum. Prepare to be shocked! G8s, G9s G11s Bush A823, T20 etc, all broken up. Of course there were a number of models that deserved such treatment

Till Eulenspiegel.

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Posted : 16/12/2014 12:58 am
Terry
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... Ex-rental sets had to be smashed up in those times. Tax reasons ...

OK - so where did all those ex-rental sets that appeared in numerous adverts in PT come from, then?

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Posted : 16/12/2014 12:55 pm
Cathovisor
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This discussion of RGB inputs has caught my eye as I note that there is a variation in colour balance between the RGB input and the composite input on my Panasonic - a slight shift towards magenta on RGB, when the composite input is correct. To add insult to injury, the colour saturation control (naturally) doesn't work on RGB!

I seem to recall that it may be a known issue with the TDA356x decoder chip in my set, but my memory may well be faulty: it's independent of RGB source so I know it's the TV.

Any thoughts?

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Posted : 16/12/2014 1:02 pm
Terry
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Assuming that the Grey Scale and White balance are correct, you are obviously missing out on a bit of green drive!

Unless there is some way of increasing the green drive, could you make arrangements to attenuate the red and blue signals slightly?

While writing this, it occurs to me that, as the G-Y signal is derived from a matrix in the decoder, that the error might begin here (excessive green) and the RGB drives adjusted accordingly ...

Would it be easier to fiddle with the matrixing and reset the RGB drives to suit - or is it all buried deep inside a chip?

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Posted : 16/12/2014 1:24 pm
Cathovisor
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Assuming that the Grey Scale and White balance are correct, you are obviously missing out on a bit of green drive!

Unless there is some way of increasing the green drive, could you make arrangements to attenuate the red and blue signals slightly?

While writing this, it occurs to me that, as the G-Y signal is derived from a matrix in the decoder, that the error might begin here (excessive green) and the RGB drives adjusted accordingly ...

Would it be easier to fiddle with the matrixing and reset the RGB drives to suit - or is it all buried deep inside a chip?

Buried inside a chip, Terry - TDA3561 IIRC. The decoder proper is a TDA4510; the chassis was a clever design of "world chassis" by Panasonic - it uses some pin-compatible Philips devices. TDA4510 for PAL, TDA4570(?) for NTSC and TDA4555 for PAL/SECAM. You can see the unoccupied holes for the FM demodulators in the print.

If I can find my copy of the manual, it'll warrant further study as I now have two of these fine TV sets! Years ago I wrote a nice little bit of software for a Psion II that calculated pads, and also reverse-engineered them from supplied resistor values - this was when we embarked on a full-scale signal path line-up of my studio in its analogue days. I think padding the R/B drives down may be the easiest option. It would have been made easier if my pattern generator (Philips PM5518TN) had the optional RGB outputs fitted! I could try using the built-in Test Card F on a Freeview box...

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Posted : 16/12/2014 3:15 pm
Electrical
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The article on “Adding a SCART Connector” from Television magazine October 1991 is now in the Library, in the Practical Television Magazine Extracts section, folder Television 1991.
Regards Stan.

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Posted : 16/12/2014 5:39 pm
Rebel Rafter
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Ah! that explains it then, that project is not aimed specifically for the TX10, but a general article about adding a scart interface to suitable sets.

I think the chap who designed the video preamp in "television" hadn't read the ferguson manual

...So no point in blaming the designer R.R! If it's a general article for adding to 'suitable sets', then it is just that. The designer is not going to know what set is being modified and will expect the reader to decide if a particular set is suitable or not presumably based on information given in the article.

Hi, RR here. That's a good point. I think I got a bit confused about what the correct composite video level should be at the o/p of a TDA2540. For some reason thorn quoted it in their TX10 manual as 3v p-p, but the datasheet for this chip shows it as 2.7v p-p, the same as the i/p level for the TDA3560 decoder chip, so they're obviously designed to work together. So this gives me the impression that the datasheet must be right. RR.

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Posted : 16/12/2014 10:09 pm
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