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 Post subject: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Wed 13, 2017 6:29 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 151
Many of you have probably encountered issues with white retrace lines and buzz in the sound when playing some DVDs on your vintage TV through an RF modulator.
These issues are due to digital data in the vertical blanking interval. This data can be copy protection signals, time code, VITS etc. Your vintage TV will expect to see black during the entire vertical blanking interval - back in those days that's what was transmitted.

The "white" data in the blanking interval often extends above peak white. This will cause problems in the sound as the vision carrier gets cut off. That, and ringing and overshoot on digitally-added text in the image will cause buzz ("caption buzz") in the sound that changes with picture content.

You can get rid of many of these issues by ripping the DVD with, for example, Handbrake or VLC. The resultant file will usually have the offending data in the VBI removed. It can then be played from a USB thumbdrive using a media player that has composite video output.

But this is tedious, particularly if you have a large DVD collection.

This issue was annoying me so I came up with a solution. A Proc Amp to remove all the undesirable signals in hardware and an AV modulator that can be tuned to a Band 1 VHF channel - I used Australian Ch2 which is close in frequency to US Ch4. This modulator also has a higher sound carrier level, reflecting normal transmitter practice before color was introduced. I chose CH2 because all TVs (10 channel and 13 channel) TVs will tune to it and because it's now a vacant channel.

I laid out an SMD board using SO and 0805 parts so that it can be assembled easily by mere mortals. Its performance is excellent and greatly adds to the enjoyment of watching old content on a vintage TV. In terms of video resolution it's equal to the Kingray professional modulator I have been using. The audio S/N is better than the Kingray.

Although it's designed for CCIR standards (Australia, Europe) it's easy to change it for EIA - one capacitor, one resistor and a tweak of the vision and sound carrier slugs.

If anyone is interested in making their own, let me know. I have some spare PCBs

Update - testing with lots of DVDs has shown an issue with some copy protection affecting the driven clamp. The LM1880 sync separator false-triggers on the data in the VBI and clamps the video level to it. So I will gate the clamp signal with the vertical blanking signal to solve this issue. When I've fully tested it I'll update the schematic.


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Legacy AV Modulator.pdf [37.24 KiB]
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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Thu 14, 2017 3:31 am 
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I like your solution -- good ol' analog design. Of course it could be built with through-hole components too, assuming the ICs are available in that kind of package, for those of us with old eyes and fingers.

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A collector of TV signal boosters and UHF converters -- God help me!
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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Thu 14, 2017 3:34 am 
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I have a "Black Box" that I picked up at a thrift store.

I know nothing about it but it absolutely does eliminate the retrace lines on DVD's, it does nothing for the white level buzz in the sound on certain sets though.
Also it runs on a 9 volt battery and has no on/off switch, i don't know if it shuts off automatically or if it'll kill the batter if I let it sit for a month.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Thu 14, 2017 3:45 am 
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Here's the innards if anyone's interested.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Thu 14, 2017 7:09 am 
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Attachment:
TV Mod.jpg
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Well here's what the final PCB looks like, after the gating fix, a screen dump from the PCB CAD.

I actually find SMD parts quicker to assemble than through hole. I use a magnifier lamp and tweezers.
But you are right, it's often a matter of what package you can source certain parts in.

I could probably reverse-engineer that black box from the chip numbers but mine's simpler!


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Thu 14, 2017 8:32 pm 
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Plus yours outputs an RF signal whereas that black box looks like it only outputs a composite video signal.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 15, 2017 6:07 pm 
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Location: Grand Chute, Wisconsin
http://bs.cyty.com/menschen/e-etzold/ar ... /uvb_e.htm


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 15, 2017 7:42 pm 
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Jim, have you tested one of those units?


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 15, 2017 10:06 pm 
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Location: Grand Chute, Wisconsin
Kevin Kuehn wrote:
Jim, have you tested one of those units?
No, not of the link I provided, but I do have one like Eric has. Works fine on all sets I've tried it on.

I found the other macrovision circuit in that link recently when I discovered the early TV page that Eckhard has up: http://bs.cyty.com/menschen/e-etzold/archiv/TV/tv_e.htm

.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 15, 2017 11:01 pm 
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The circuit that Jim posted will suffer from the same issue I encountered - the clamp reference will be disturbed by the copyguard signals and so not clip accurately in some cases. Plus it seems to clamp to sync tips and not the front porch - acceptable most of the time but not ideal.

But it's very similar, an LM1881 and a mono! Great minds and all that! I'll be extensively testing my modified circuit this weekend.

I'm surprised that many others have this problem. Makes my little effort seem worthwhile!


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Mon 18, 2017 6:24 am 
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Well my gated clamp works a treat but it's shown up a mistake in the formulas I used to calculate the resistor values in the reference voltage string. A + instead of a -!
It's so easy to just accept the numbers calculated by a spreadsheet and not do a proper reality check! A VERY dumb mistake!
Even with the wrong values it works OK, it's only when I looked at it on the scope I found the mistake.
The scope also showed that the video was 2dB down at 4.4MHz, Not so bad but there were also some rounded edges to degrade the image. I can fix that too.
I'll fix it tomorrow, retest and put the revised schematic up.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Thu 21, 2017 5:55 am 
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Updated schematic is attached. I ended up using the spare analog switch to gate the clamp.

Attachment:
Legacy AV Modulator.pdf [37.34 KiB]
Downloaded 60 times


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Thu 21, 2017 3:32 pm 
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This is amazing work, thanks for sharing! I recently was wondering if there was a way to do just what this does. I downloaded the schematic and hope I can make one someday.

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I don't own too much old stuff, I just temporarily take care of it for it's next owner.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 22, 2017 4:50 am 
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I also have one of those digital video stabilizers like Eric has, but I never had to use it to play DVDs on my 1990 Magnavox 27" floor console. In fact, I've been using an old 25 year old Samsung DVD player to play the DVDs, and I've noticed nothing wrong with the picture or sound. I mainly used that stabilizer for Macrovision encrypted video tapes.


Last edited by Blustar1 on Dec Fri 22, 2017 3:14 pm, edited 1 time in total.

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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 22, 2017 11:13 am 
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Newer TVs like yours don't usually need this. 1970s and earlier usually do.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Sat 23, 2017 2:49 pm 
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Joined: Dec Fri 22, 2017 11:55 am
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Location: Tampa FL
Read the December '87 issue of Radio Electronics at americanradiohistory.com. This is called Macrovision,
and has been around a long time. Even back to the video cassette era, and on into the dvd era. A very in depth
article on how it works, and a superior kit project to eliminate its effects. I think it works better than the newer units.
Kurt arcade-antiques


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Sun 24, 2017 6:45 am 
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Joined: May Sun 07, 2017 11:35 am
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Macrovision is not the only system that puts crap in the VBI. Some of the other culprits are:

VITS (Vertical Interval Test Signal)
Teletext
Timecode

These will often be seen on over-the-ait TV recordings

Apart from Macrovision there are a number of other copy prtotection systems as well as in-house systems used for tracking illegal copies that don't really try to stop the copy being made by mucking up the video AGC as Macrovision does. I wanted to make something that was completely agnostic, that simply restored the VBI to what it used to be. As well as eliminating "caption buzz" when using a modulator.


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 29, 2017 1:02 am 
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Joined: May Sun 07, 2017 11:35 am
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Some questions from another forum also raised the issue of what TVs will need this.

It's safe to say that most TVs made after about 1976 won't have a problem because, by then, the insertion of data into the VBI had become common practice and the TV receiver needed to cope with it.

Rigorous vertical blanking (i.e. capable of blanking video at peak white) using a signal from the vertical output is just about impossible to achieve using only passive components. If the time constant is too long it will cause shading at the top of the picture. The blanking needs to be digitally generated to be effective. So tube TVs from the 50s and 60s rarely have 100% effective vertical retrace blanking, simply because they didn't need to.

In Australia we had an early color NEC chassis that was caught out when Teletext was introduced. A modification kit was released that consisted of a two transistor monostable on a little PCB that was screwed to the side of the deflection chassis and wired into the blanking signal path.

Now I don't recall blanking ever being an issue with early TVs when teletext was introduced in the mid 70s, but that could be because the vast majority of B&W TVs were already in landfill by then. The changeover to color happened very quickly in Australia.

Another thing that happened here is, in about 1969 from memory, the level of the transmitted sound carrier was reduced from (I think) 25% to 10% of peak vision carrier, in preparation for color (reduced IM beat in picture). This information was released to the TV service industry but we were told "don't tell the customers, they won't understand"! Some early TVs already suffered from marginal sound and the change didn't help.

As it turned out, the change wasn't really needed because, by 1974, technology had moved on and the prime cause of the sound-chroma beat, the diode detector, had been largely superseded by the synchronous demodulator.

Did that also happen in the US?


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Dec Fri 29, 2017 2:52 am 
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irob2345 wrote:
Another thing that happened here is, in about 1969 from memory, the level of the transmitted sound carrier was reduced from (I think) 25% to 10% of peak vision carrier, in preparation for color (reduced IM beat in picture). This information was released to the TV service industry but we were told "don't tell the customers, they won't understand"! Some early TVs already suffered from marginal sound and the change didn't help. . . . Did that also happen in the US?
In the following discussion, a former broadcast engineer described how in the US, the aural power was reduced in a series of steps, starting in the early 1950s:

viewtopic.php?f=3&t=315127

Regards,

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: Playing copy-protected DVDs on old TVs - a solution
PostPosted: Jan Mon 22, 2018 3:25 am 
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Joined: May Sun 07, 2017 11:35 am
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I thought I'd post a pic of what the Macrovision looks like on a TV that can't blank it properly:
Attachment:
Retrace blanking.jpg
Retrace blanking.jpg [ 26.63 KiB | Viewed 533 times ]

Also, after making a number of these boards and observing some white crushing with some of them, I've found that a slight change to the modulator bias is needed. Shunt R28 with 100k or use a 6.43k resistor.


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