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Old 15th Mar 2018, 9:16 pm   #1
nmiddlemass
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Default Decca Colour DT1263 Microsystem Television - Colour Query

Hi.

I've recently been gifted a Decca Colour TV. The model number is DT1263 (This is the only number I can locate on the unit)

I'm not a television expert and cannot find an online service manual for this model so I'm hoping someone may be able to save me some trial and error.

The TV turns on OK.

However, the screen is a little dark unless I turn the brightness up to full but the main issue is that the picture looks like it has a yellow filter.

Any interference on no tuned channels has this yellow tint and when I turn the colour right down it still has this.

I have located the internal RGB adjusters but I'm not 100% sure adjusting this balance will fix the issue although I may be wrong.

Would anyone be able to provide me with any advice on what may be causing this?? Or is the tube just shot.. Would be a shame because the picture is nice just a bit yellow.

Thank you..
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Old 15th Mar 2018, 10:00 pm   #2
simpsons
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

According to the webb, electrotanya model equivalent chart shows your TV as a 120 chassis.

Threads and a service manual are also easily obtained on the web. One such web site suggests early Mullard 20AX CRT's didn't last too long. However there is a bodge you will find.

As for adjusting RGB drives etc, I would not unless already twiddled and before you do make sure the tube is not suspect. Then, follow the service manual instruction.

Good luck


Chris
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Old 16th Mar 2018, 1:56 am   #3
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Decca-Tatung 120 series chassis was designed to drive Toshiba inline CRTs.
The 130 series employed the Mullard 30AX CRT.
Try giving the A1 pot on the line output transformer a tweek.

DFWB.
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Old 16th Mar 2018, 4:22 pm   #4
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

The resistors in the RGB circuit used to change value giving various grey scale problems. The CRT is probably OK - they were quite long lived in this chassis.
This was the first Tatung chassis, and was far more reliable than the Deccas that preceded them, well liked though they were. Once they became big black and ugly, Tatungs were nowhere near as good as this chassis so it would be nice to hold onto it.
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Old 17th Mar 2018, 3:22 pm   #5
nmiddlemass
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Thanks to everyone for words of advice..

This TV has a Tatung 510UFB22-TC05 tube and a 120 series board.

I have located one burst resistor which I am yet to replace.

Would anyone be able to point me in the direction of a service manual?? I've had a look on Google but struggling to find anything.

Many Thanks

Neil
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Old 17th Mar 2018, 5:13 pm   #6
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Quote:
Originally Posted by Welsh Anorak View Post
The resistors in the RGB circuit used to change value giving various grey scale problems. The CRT is probably OK - they were quite long lived in this chassis.
This was the first Tatung chassis, and was far more reliable than the Deccas that preceded them, well liked though they were. Once they became big black and ugly, Tatungs were nowhere near as good as this chassis so it would be nice to hold onto it.
Tatung was a product That never really made it here, even in private label products.
I remember them building a Beta VCR but never saw one of them either.
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Old 17th Mar 2018, 7:30 pm   #7
simpsons
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Search for Decca Series 70 service manual to downlod FOC chassis details. Should the 130 follow the basic design, then the follow applies

5.2.7 Grey-scale Tracking
5.2.7.1 Set the user colour saturation control (VR701) to minimum and
disconnect the luminance feed link TL201.
5.2.7.2 Rotate the A1 voltage preset control VR908 clockwise ()n the tube base panel) until the raster blanks out and then bring the control
back until the first colour is visible. If no colour is visible then adjust the green background control (VR254) anticlockwise (viewed from the copper side) until the raster just appears.
5.2.7.3 Bring up the two remaining colours by the adjustment of the appropriate background controls to give the correct grey setting.
5.2.7.4 Re-connect the luminance feed link and adjust the three drive controls VR232, VR233 and VR234 as required to eliminate any colouration of the highlights - this should require only slight adjustment of one or two of the controls. (Anticlockwise adjustment from the copper side increases the drive). Repeat para. 5.2.7.3 and para. 5.2.7.4 as necessary. If, after a number of adjustments, the results are unsatis factory, reset as in para. 5»2.4.3. and repeat para, 3«2,7

Hope this helps

Chris
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Old 17th Mar 2018, 8:19 pm   #8
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

hi, yes we did loads of these sets going back in time, its the 120 series chassis. if i remember rightly on the crt base there are three banks of resistors in each output stage [making 47k if memory serves me right] change all 9 then all will probably be o/k unfortunately gave away all the service info we had last year .
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Old 17th Mar 2018, 10:07 pm   #9
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi

There was a good servicing article on the Decca 120/130 series chassis in the October 1988 issue of Television magazine by Nick Beer.
In the article he mentions a loss or lack of one colour is generally caused by the appropriate feedback resistor in the RGB output stages. These are R226 (red), R244 (green) and R251 (blue). Their value is 100kΩ, 2% tolerance.

He also quotes useful RGB o/p stage voltages:

Q203/8/11 7.6V emitter, 8.2V base, 136V collector.
Q204/10/12 1.4V emitter, 2.1V base, 7.6V collector.

Also, the c.r.t in the 120 series chassis should have 10V at its grids (pin 5), 600V at its first anodes (pin 7) and 136V at its cathodes (pin 6 green, pin 8 red, pin 11 blue). I assume these voltages are with a meter of 20kΩ/V sensitivity such as an Avo model 8 or similar.

The chassis was covered in the 1982-83 edition of Radio and Television Servicing.

As you probably know this chassis is always live regardless of the mains supply polarity.

Regards
Symon.
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Old 23rd Mar 2018, 9:51 pm   #10
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

I wonder how the OP is getting on with the grey scale problem.

Regards
Symon.
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Old 24th Mar 2018, 9:56 pm   #11
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi Everyone,

Thank you for all your help with this and kind words of advice and encouragement.

I have replaced some resistors that had shifted in value and also redone a couple of bad solder joints.

Having done all of that the set still has an issues, although it is now fairly clear what the issue is, I just don't know how to fix it...

On the board connected to the CRT there are background controls for R, G and B as well as ones to drive the RGB highlights.. (I hope I am not sounding like a complete idiot here)..

If I adjust the background controls there is a big change in R and G but the B channel does nothing.. However there is blue coming through the highlights..

So the yellow tint is still present but you can see blue highlights...

I will check R251 as Symon has suggested and see what that does as well as Q203/8/11 and Q204/10/12

If anyone reading this knows anything else that could be causing this I would love to hear..

Thanks again.

Neil
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Old 24th Mar 2018, 10:48 pm   #12
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi Neil.

It would be a good idea to first check R251. It's probably best not to twiddle the background and drive controls without first noting their original position. The A1 pot (associated with the focus pot) in the line output stage may need to be set up. It's important the A1, background and drive presets are correctly set to obtain optimal grey scale and to avoid over driving the CRT. Make a note of the position of the A1 pot and try slight adjustment to see if it improves matters.

Regards
Symon
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Old 25th Mar 2018, 12:07 am   #13
nmiddlemass
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi.

I've hopefully attached a picture of R251. Symon, does your information say what the value should be for this resistor?

This board looks like it's been fairly hot at some point..

Really appreciate your interest and support with this.. this is my first TV so I'm learning all the time.

Regards

Neil
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Old 25th Mar 2018, 10:03 am   #14
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi Neil.

R251 is 100kΩ 2%. The colours of the 5-band resistor colour code Brown Black Black Orange and Red for the 2% tolerance band. It looks like a metal film resistor but I'm not sure of its power rating, probably around 0.5W. A modern higher power rating type would be preferable.

It's best to check R226 and R244 in the red and green stages respectively, as well.

Any chance of a pic of the display showing a grey scale step test pattern?

Regards
Symon.
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Old 26th Mar 2018, 10:43 am   #15
nmiddlemass
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi..

I removed the 3 100k ohm resistors R226 (red), R244 (green) and R251 (blue) from the circuit and tested them..

R226 and R244 were misbehaving a little bit coming in at 120k ohm and R251 was clearly the an issue reading 1.25M ohm!

I replaced all of these with new and the yellow issue is now gone.. Result

The colour channels are now looking imbalanced but the blue issue i now corrected.

Thanks to everyone for helping me and Symon for the detail around the R251..

I would imagine the next thing t do is get a test card through the screen to balance the colour or would it be best to start with a grey scale step? Is there a resource anywhere for getting testcards etc??

Regards

Neil
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Old 26th Mar 2018, 3:14 pm   #16
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi Neil.

I am pleased you have sorted out the main problem.
There's a great set of testcards and test patterns from member Mikey405 which can be burnt to DVD. See this page https://www.vintage-radio.net/forum/...t=71637&page=3 and specifically the latest version here: http://www.oldtechnology.net/TestCar..._Christmas.iso
Only slight snag is you will need a UHF modulator to connect to your DVD player as your TV is RF in only ie no SCART or AV in/out facilities.
TV pattern generators do crop up on ebay from time to time, alternatively, a simple TV pattern generator with UHF modulator can be easily built.

Regards
Symon.

Last edited by Philips210; 26th Mar 2018 at 3:26 pm.
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Old 26th Mar 2018, 3:55 pm   #17
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Don't forget an old video recorder can be used as a modulator. The mechanics don't need to work, just as long as it switches on and you can select an AV channel you're there.
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Old 26th Mar 2018, 3:56 pm   #18
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Yes, very good point Glyn.

Symon.
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Old 31st Mar 2018, 11:11 am   #19
nmiddlemass
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Default Re: Decca Colour DT1263 Microsystem Television - Colour Query

Hi,

I have finally managed to get the colour balanced on this set and it looks fantastic. I'd forgotten how clear these things looked especially with a DVD running through the VCR.

Thank you to everyone for the invaluable help, tips and advice on this.

Regards

Neil
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