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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 18th Aug 2019, 11:18 pm   #1
Richard_FM
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Default Screen Tearing on Pye BX1016 on Video playback

Today I tried out connecting my Pye BX1016 to my Sony SLV-E730 VCR using the RF cable.

The on screen displays seemed fine but when playing a tape the top 10% of the screen was tearing. I tried adjusting the tuning, tracking & output channels but this didn't seem to make any difference, as did adjusting the vertical hold on the TV.

The fact that I tried 2 pre-recorded tapes makes me think it's possible macrovision affecting the picture, I didn't have a home recorded tape to test out.

I'm sure I've not had this issue before with other old TVs, & the picture was fine on my main TV through the Scart output.

I didn't have time to try every troubleshooting method I could do.

I know some older TVs can have trouble displaying a non-broadcast source, but hadn't encountered this before.
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Old 19th Aug 2019, 11:01 am   #2
SteveCG
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Some 1980s TVs used a special channel button (certainly the Thorn TX 10 chassied sets did) which had a shorter line timebase, flywheel sync, time constant to address this effect.
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Old 19th Aug 2019, 11:23 am   #3
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Try the highest preset. If that doesn't work the set might need to be modified.

It isn't so much the non-broadcast source but the instability of the horizontal time base on video tape recordings. It could also help to adjust the back tension of the tape a bit.
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Old 19th Aug 2019, 1:31 pm   #4
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Thanks for the advice, I'll try the suggested solutions when I can & like you all know if they improve things.
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Old 19th Aug 2019, 3:17 pm   #5
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Default Re: Screen Tearing on Pye BX1016 on Video playback

try tuning in the vcr to channel 0
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Old 19th Aug 2019, 7:47 pm   #6
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Please double check your tv model number, once we identify the chassis we are in with a shout.
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Old 19th Aug 2019, 10:30 pm   #7
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Default Re: Screen Tearing on Pye BX1016 on Video playback

I think a TX chassis. Probably 12BX1016 or 14BX1016 (only 1 of those will exist, no idea which).
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Old 19th Aug 2019, 11:04 pm   #8
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Default Re: Screen Tearing on Pye BX1016 on Video playback

It's a 31BX1016/5S (a rare use of cm to express a screen size in a model number)

https://www.vintage-radio.net/forum/...d.php?t=154076

I've tried again with some different tapes & it seems to be OK on ones without macrovision.

Tuning on button 6 doesn't make any difference, I guess as the basic TX chassis design is from the mid-late 1970s there isn't anything special on the circuitry to sort this out, especially as macrovision didn't come around for a few years.

I know Maplins used to sell a "video smoothing" device that would correct reverse the effect of macrovision (not mentioned anywhere in the instructions!), but I'm not worried enough to track one down.

My other sets seem to be OK with it, my Toshiba certainly seemed to behave, not tried the Fidelity yet.
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Old 19th Aug 2019, 11:32 pm   #9
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Hi Richard,
The problem with the signal from a VCR is jitter in the line sync pulses. Due to their mechanical imperfections, the timing of the line sync pulses varies between the odd & even fields which are recorded sequentially by each video head.

Tv's from the dual standard era onwards had 'flywheel sync' which was designed to cope with weak or missing line sync pulses caused by weak signal. It can't cope with the rapid change in timing of the sync pulses from a VCR, so picture tearing at the top is the usual symptom.

Different TV's cope better than others and as has been said, there was usually a button specifically for the VCR. This altered the time constant of the flywheel sync circuit. Usually the highest or lowest button.

The problem is usually better when the VCR is playing one of it's own recordings. It will usually be worse with pre recorded tapes, but will have nothing to do with Macrovision which affects the AGC. Sometimes careful adjustment of the line hold (not the frame hold) can help.

Sometimes the TV needs to be modified, but this can not always be done satisfactorily. I have a PYE CT205 hybrid colour set, which despite spending many hours trying different mods to the line oscillator/ flywheel sync circuits, still won't work well with a VCR.

Hope that might help,
All the best
Nick
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Old 19th Aug 2019, 11:32 pm   #10
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Right, it appears to be a tx3
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Old 20th Aug 2019, 1:21 pm   #11
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Thanks again for the advice, I'll have another look when I can, but normally I'm a bit too busy mid week to do much.

Philips managed to make a lot of different models for the TX family (& in lots of their factories too!), & occasionally I still find pictures online of ones I didn't know existed.
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Old 21st Aug 2019, 10:54 pm   #12
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Quote:
Originally Posted by Maarten View Post
Try the highest preset. If that doesn't work the set might need to be modified.

It isn't so much the non-broadcast source but the instability of the horizontal time base on video tape recordings. It could also help to adjust the back tension of the tape a bit.
I second trying the highest preset. I used to have a Pye Studio Colour set from the 1980's, and it did this. I can't remember the model of mine but it was a basic, non remote control set, with a 20'' screen. Channel 12 which was the last of the presets was the VCR channel on mine. I remember the power switch stuck on mine too and having to switch it on/off at the mains.
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Old 22nd Aug 2019, 7:39 pm   #13
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Default Re: Screen Tearing on Pye BX1016 on Video playback

oops did,nt realise it was just a 12in mono set, try tuning the vcr in to ch8 ??a lot of pye/philips sets [colour] used either the highest channel number 12/16 etc or number 0
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Old 22nd Aug 2019, 10:46 pm   #14
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Thanks for the suggestions

There are 6 channel switches & using number 6 doesn't seem to make any difference.
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Old 24th Aug 2019, 5:27 pm   #15
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Default Re: Screen Tearing on Pye BX1016 on Video playback

The may 1982 edition of TELEVISION magazine contains an excellent article on the subject of TV-VCR compatibility by the esteemed writer, Eugene Trundle.
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Old 24th Aug 2019, 9:05 pm   #16
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Thanks for letting me know, are there any online scans?
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Old 24th Aug 2019, 10:09 pm   #17
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Default Re: Screen Tearing on Pye BX1016 on Video playback

Practically all horizontal AFC (automatic frequency control) systems sample a signal from the H output stage and compare that to the phase of the sync pulse to generate a "filtered DC control voltage" for the H scan oscillator. It is the same concept as a PLL.

Since the H oscillator becomes DC controlled (not triggered by individual H syncs as it was in early TV sets) there is a limit to the speed at which it can respond, say if the H sync phase suddenly changes after head switching in a video signal from a VCR. If the control voltage can change fairly rapidly, say after a few scanning lines the tear in the image is not too bad, but if its 10 or 20 lines or more there can be a big tear.

Often the physical head alignment in some VCR's isn't wonderful and there is a bigger phase error at head switching. In other words the heads are not exactly physically 180 degrees apart which is how the phase error comes about, but as noted the tape back tension also generates a phase error if it is different on the recording and playback machinery. But, on the same machine therefore, it is still possible to have the big tear on a record-playback because of the head alignment. You will notice head drums have a hole leading down beside each head, this is used, with a special tool, to move the head position on the perimeter of the drum. (Don't attempt that if you are not trained to do it, its tricky)

If you look at the components at determine the DC filtered control voltage in the AFC there are generally three. A main filter capacitor, and in parallel with that a larger value capacitor with a series resistor. These two series components across the main filter cap form an "anti-hunt network" to prevent the H osc hunting around when locked.

In most cases it is just a matter of altering the time constant of that filter network ,by reducing the value of the capacitors, to speed up the reaction time of the H oscillator. Usually it does not affect the result with a stable broadcast signal, perhaps only make the H lock system slightly less noise immune. And you should get a much better result with the signal from the VCR.
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