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 Displaying new content from DVDs on early TVs - reprise.
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 Return to top of page · Post #: 1 · Written at 2:07:01 PM on 30 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 578

As a hardware designer approaching retirement and with several projects at work delayed by software/firmware development running late (the hardware's been ready for a year now – where's the software??!) I find I have time on my hands.

I need a hardware-only project!

After fixing Pete's Philips and several other old TVs I've found a common theme – how do we play modern content from DVDs on old TVs without issues that make the result tiring or impossible to watch?

Some of the issues I've encountered are:

1. Getting a video and audio signal onto a VHF carrier on a frequency that the TV can tune to (mainly an issue with early TVs fitted with 10 channel tuners).

2. Buzz in the audio caused by overshoot on peak whites (e.g. text) in the image and digital data in the vertical blanking interval.

3. Marginal sound on some TVs that were designed to the original standards of 25% sound to peak vision carrier (before colour was introduced). My AWA is one of those.

4. Thin white diagonal lines superimposed on the picture, also due to digital data in the vertical blanking interval that the TV's vertical blanking circuits can't remove. This last issue seems to be on certain content only. (I modified my Kriesler to fix this. It needed a monostable in line with the blanking signal).

5. A grey “watermark”, visible on dark scenes on TVs with AC coupled video caused by the colour burst signal. You can fix this by adding horizontal blanking to a set that doesn't have it (like I did to my AWA) or using the Y signal only from your DVD player's Y/C output.

6. Sync issues (mainly rolling and jitter) caused by letterboxed images (i.e. 16:9 content formatted with black bars top and bottom). This seems to be a problem with some TVs more than others.

All these issues are due to the TV trying to work with a signal that wasn't around when the TV was designed.

How many collectors of old TVs believe there's a need to solve these issues?

Sure you can modify the sets to fix sync and blanking deficiencies and even inject video and audio directly, bypassing half the TV. But that defeats their authenticity. A bit like putting an electric motor in a vintage car...

If there is interest in this I'll put up a design brief for a video processor and VHF modulator that's been rattling around in my head for a while and invite comments as to what it should, or needn't, have in its feature set.

But briefly:

The video processor would have the ability to remove everything from the VB interval, replacing it with black level. It would allow you to replace black letterbox bars with grey ones and optionally remove the colour burst. Peak whites would be clipped and slew limited to avoid white overshoots punching holes in the sound carrier. The entire video signal would be brick-wall filtered for the same reason.

For the video modulator part, should the vision carrier be continuously tunable (keeping it simple) or locked with a PLL to channel frequencies? And do we really need a vestigial sideband filter with its added complexity? Most VCR modulators didn't have VSB filters....

Oh, and switchable 25% sound carrier, since we aren't interested in colour.


 
 Return to top of page · Post #: 2 · Written at 4:06:46 AM on 31 July 2017.
Vintage Pete's avatar
 Location: Cromer, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 564

Some of those issues ,I have had ,but their inconsistent. I had a Pye Pedigree about 66 model and it would get the white lines,but yet the Pye Technico which is much older and is a 1958 model does not seem to get it.
But its been a long time now since I have used either of those tellies as their in the storage unit. But I do remember the Pye Pedigree got the white lines bad.
This device you have in your thoughts, Is it external and would completely also take the place of VHF modulator .
All in one unit in other words?
I saw a post once where the guy had also completely got rid of the VHF adapter plug from the antenna outlet and just installed the red, yellow , white jack plugs instead.
There are not many TV collectors in Oz, in all the years I have been involved in this I have only known 2 other nutters like myself.but in the UK its much bigger and has many followers.

Pete


 
 Return to top of page · Post #: 3 · Written at 11:32:22 AM on 31 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 578

Yeah Pete, it can depend on the design of the vertical blanking in the TV and the content.

The idea is it would take the place of whatever modulator you are using.

Yes I'm aware the market would be very limited. I might send an email to the museum in Ohio to see if there is interest there. 405 line TV in the UK is already pretty well covered.

Connecting AV into the TV directly appeals to me about as much as pulling the motor and gearbox out of your old car, attaching an A frame and towing it behind your Modern.

And I know how to get direct AV into a TV and make it work properly, I did just that for years as a business, ended up making and selling the mod kits to AWA and NEC - in the latter case replacing an imported Japanese assembly.


 
 Return to top of page · Post #: 4 · Written at 12:18:54 PM on 31 July 2017.
Vintage Pete's avatar
 Location: Cromer, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 564

Hi Ian,
There will also come a time ,when vhf modulators and digital box convertors will no longer be available in Electronic shops.
No demand.
Well , if you decide to go ahead with your idea, I would be wanting some for sure.
Pete


 
 Return to top of page · Post #: 5 · Written at 1:42:43 PM on 31 July 2017.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 184

Hi Ian, yes i'm sort of interested as well.
While I'm playing about with my 5" and 3" valve TV sets and learning some basics I'm conscious of the fact that I too am using an "A" frame to tow my valves behind a set top box! I'm right in the middle of trying to get Miller Frame and Line oscillators to lock up onto the video signal coming out of the STB without phase shift , jitter, rolling and all that jazz from all those chominance and weird extra signals and having much fun doing that and will get there.
However I quail at the thought of rolling my own tuner and IF strip, with valves of course, to suit the latest signals!
I guess that's what a STB is but no valves.
Perhaps maybe one could compromise with:1/ a "Ian" video convertor to scrub out all the colour crap from a STB output and leave just the Luminence for picture and blanking bars to lock the sweeps up on for non tuner/IF strip types like mine and 2/ an "Ian" convertor that does the UHF conversion to channel 1 for those with unmolested sets? Perhaps your "Ian" convertor design could have 2 outlets: A/ to antenna socket and B/ to video detector test point?
Cheers, Fred.


 
 Return to top of page · Post #: 6 · Written at 1:53:54 PM on 31 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 578

Quick way to get a signal without the chroma is to use the Y output from your box's Y/C (S-Video) connector. And make sure it's running full screen.

Valves are really crap at being sync separators! Transistors do a much better job.


 
 Return to top of page · Post #: 7 · Written at 2:39:58 PM on 31 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 578

Fred, I just had a thought....

Your STB has a VGA output, right?
Does it still output sync signals when it's set to composite video out?
If so, you'll already have some nice, clean, unmolested TTL level signals on pins 13 and 14 that are already separated into H and V. Hopefully when composite is selected they'll be at PAL frequencies. Worth a check I think.

If I'm right, why bother trying to get your sync separator working?


 
 Return to top of page · Post #: 8 · Written at 5:35:52 PM on 31 July 2017.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 184

Ian you will laugh at me, my response to your last was...um..ah...oooooooooooooooh...so that's why there are all those extra sockets on the back of a STB!! Being a complete noddy with video stuff my knowledge did not go past the yellow, white and red sockets!
I'm currently working with a cheapo STB with only a y/w/r rca sockets but do have another STB with ALL those other sockets.
Looks like I need to swap to that one and learn about what comes out of all those funny shaped sockets!!!

I did reach a 'satisfactory' set of locking signals for my 3" set, able to lock both Miller sweeps tightly with plenty of range on the adjusting pots and the phase relation so the sweeps start just about where they should without the blanking bars in funny places!
Now that you have alerted me to the STB possibilities I may do better still.
Cheers, Fred.


 
 Return to top of page · Post #: 9 · Written at 7:17:24 PM on 31 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 578

Yeah, Fred, just google VGA pinouts and you'll have your connections. Same goes for the s-video if it has one.

VGA is an analogue standard where the 3 colours - Red, Green and Blue come out as discrete 1v pp signals on pins 1,2 and 3 respectively.


 
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