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405 line NTSC Chip decoder.

 
Red_to_Black
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The TDA3562A chip is a difficult beast to work with in a set not designed for it, the auto greyscale being a fly in the ointment, if this is not correct it shuts down the outputs.

I did have a circuit (bodge) for fooling this part of the chip, but would it not be easier to use the TDA3560/61A ?

Edit: I corrected the chip numbers, I mistakenly transposed the 5 and 6, you won't get any colour out of a frame chip. :qq1

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Topic starter Posted : 17/11/2013 11:08 pm
Anonymous
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I modified a PAL only TX10 to do composite in non-standard NTSC with two frequencies, 525 30fps 60 Hz NTSC 4.43MHz from a video cassette and also a weirder 625 25 fps 50Hz NTSC on a different frequency from a computer. Crystal switched with an added sub-miniature relay, as was other functions. I think I used the Teletext option pins for RGB in too. (No teletext). Maybe 1982. The NTSC was unstable :)

525 30fps 60Hz only needs the height adjusting. So maybe you can try 525 "real" NTSC first on a single standard PAL only set as an introduction?

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Posted : 17/11/2013 11:41 pm
Cathovisor
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The TDA3562A chip is a difficult beast to work with in a set not designed for it, the auto greyscale being a fly in the ointment, if this is not correct it shuts down the outputs.

A former colleague once remarked that the problem with using Philips chips of this era was the need to wrap the rest of the telly around them to make them work! I'd have thought a better chip to use was the TDA4570, a 16 pin device. Like all Philips chips of that era, you're still going to have to make the sandcastle pulses.

My Panasonic CRT TV actually has the PCB laid out to use the multi-standard TDA4555 instead of the fitted TDA4510 (these chips were designed to have pin compatibility); this was so it could be used in Europe where it might have to deal with PAL and SECAM signals. Sadly there was no option to switch crystals for PAL and NTSC though!

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Posted : 18/11/2013 12:36 pm
Red_to_Black
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Another thought springs to mind, most/all of the chips mentioned so far give outputs in RGB format for cathode drive.
how much of a problem is this if your D/S set uses CDA drives ? or is it possible using say the TDA3565 or similar to just omit the luminance signal to the chip ?

As you can tell I am very interested in what you come up with Trevor :aad , I love stuff like this. :thumb

Edit; Just noticed the TDA3565 appears to be PAL only, so I can forget that one! :cch

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Topic starter Posted : 18/11/2013 10:56 pm
Red_to_Black
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No problem getting B-Y and R-Y from some decoder chipsets but G-Y is more of a nuisance. Not sure if you can derive it without Y, I'd need to think about it. If you don't need Y to get G-Y then in my design using a TDA4510 etc you could disconenct Y from the TDA3505 and get a set of colour diff signals.

That is sort of along the lines I was thinking Jeffrey :aad , likewise I was not sure if you could just disconnect the Y drive from certain chips/chipsets, although I have seen faults with an O/C Y delay line, and the outputs still function in a fashion.

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Topic starter Posted : 18/11/2013 11:16 pm
Cathovisor
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TDA4555 and TDA4556 give R-Y and B-Y signals: one chip gives the inverse sense of the other. Both are multi-standard (PAL/SECAM/NTSC) devices.

TDA4570 (NTSC only) is £7.19 or less from eBay suppliers: TDA4555 is £5.65.

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Posted : 18/11/2013 11:17 pm
Red_to_Black
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TDA4555 and TDA4556 give R-Y and B-Y signals: one chip gives the inverse sense of the other. Both are multi-standard (PAL/SECAM/NTSC) devices.

That looks quite a good chip to play with Cathovisor, out of the Alpha 2 chassis ?

Edit:At least the Alpha 2 uses the TDA3505 in conjunction with it, and no messy I2C controls to worry about as far as that chipset is concerned, unlike later devices.

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Topic starter Posted : 18/11/2013 11:32 pm
Refugee
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The drives can be inverted with one of these chips with care as they could go into oscillation if the layout is not taken care of.
I have got three types of triple video op-amp chip with enough that I can spare a couple.
They are National Semiconductor devices LM1203, LM1205 and LM1207 and are all NOS.
They drove the video output transistors on VGA screens and there are two output configurations.
The data sheets are easy to get and I have a couple of home brew projects up and coming that may use a couple of one type.

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Posted : 19/11/2013 12:43 am
Red_to_Black
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The drives can be inverted with one of these chips with care as they could go into oscillation if the layout is not taken care of.
.

It is not as simple as inverting the drives Ref, that would be fairly easy to arrange, even a single transistor per stage could do that, CDA uses colour difference drives, part of the matrixing is done in the CRT itself.

What is needed is to take away the luminance from the RGB signals, R-Y, B-Y, and G-Y, granted this could be achieved by using video op-amps with the Y signal inverted and added to each RGB output.

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Topic starter Posted : 19/11/2013 12:52 am
Cathovisor
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TDA4555 and TDA4556 give R-Y and B-Y signals: one chip gives the inverse sense of the other. Both are multi-standard (PAL/SECAM/NTSC) devices.

That looks quite a good chip to play with Cathovisor, out of the Alpha 2 chassis ?

Yep, that's the one. Wonderful TV, may it go on forever :) Good pictures, GREAT sound - just what I want from a TV. And a 4:3 CRT too :thumb

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Posted : 19/11/2013 1:25 am
Refugee
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I agree that the chips I have are only useful for buffering and interfacing around the standards switching as they can be internally switched so that the outputs become open so that a DC voltage would only need to be on a single pole switch in order to flip the R.G.B. over between two of them.
.

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Posted : 19/11/2013 3:24 am
Terry
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As the idea is to end up with a an NTSC-405/PAL-625 receiver, surely it makes sense to take advantage of the multi-standard TDA4555?

This could simplify the interface to the existing receiver and allow flexibility for incorporation in a wide range of sets.

Unfortunately, my collection of Mullard Technical Communications suffered from several office moves and I can't find the issue I want but one features a full discussion of the design procedures for the use of the TDA4555 including a fully worked prototype design.

As with all such designs in MTC, this would include full winding details for all the inductors involved for both 625 and 525 line standards and the latter can easily be re-worked to suit NTSC-405 frequencies.

If someone can find a copy it could be very useful to you, Trevor.

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Posted : 20/11/2013 11:04 pm
crustytv
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Hi Trevor,

Whatever happened to your original 405 colour project , and what became of the Decca CTV22 ?

For those that were not aware you can follow the very interesting thread here http://www.vintage-radio.net/forum/show ... +line+ntsc

Was it really six years ago :ccf

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Posted : 21/11/2013 12:55 am
Cathovisor
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Unfortunately, my collection of Mullard Technical Communications suffered from several office moves and I can't find the issue I want but one features a full discussion of the design procedures for the use of the TDA4555 including a fully worked prototype design.

As with all such designs in MTC, this would include full winding details for all the inductors involved for both 625 and 525 line standards and the latter can easily be re-worked to suit NTSC-405 frequencies.

The "serving suggestion" in the TDA4555 datasheet is quite comprehensive, but no doubt not as comprehensive as the MTC would have been.

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Posted : 21/11/2013 1:03 am
Till Eulenspiegel
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Hi Trevor,
I have no information to hand for the Motorola decoder chips that were in common use in the seventies, however, these chips might be suitable for 405 NTSC.
It would appear that the TDA35XX series of colour decoder chips are made exclusively for the PAL system.

Till Eulenspiegel.

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Posted : 21/11/2013 2:19 am