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 Post subject: Sony TV external video input mod
PostPosted: Sep Sat 21, 2019 9:56 pm 
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Location: Warner Robins, GA
I have an old 5" B/W tv and wanted to make it into a scope clock.

I thought of modding the TV but realized that might not work.

So what I need is a box or circuit that can convert an X Y Z signal into a standard NTSC composite video signal which I can then feed to the TV.

EDIT:

Looked online and what I am wanting to do is not going to be easy.

That said the clock uses a DAC so perhaps it would be easier to convert the digital signals to composite.

EDIT 2:

Here's part of the relevant portion of the TV schematic.

Attachment:
TV.png
TV.png [ 157.22 KiB | Viewed 1532 times ]


I'm thinking perhaps I'll add a video input so this can be used as a B/W display for now.

Looks like I can break the connection at the red arrow and use that for the video input.

Now there is custom firmware for the clock board that allows a variable refresh rate which I can load on a clock board.

Was done for someone who wanted to display the clock on a TV.

I suppose that it wouldn't be too hard to disconnect the oscillator output from the deflection amp stages and try the clock just to see how it displays.

My concern is how the CRT anode connector voltage is generated. Relies on the horizontal amp section.

Pretty sure it is not designed to handle anything but the NTSC horizontal sweep frequency.

Would be nice if I knew who the person was that tried to make the scope clock display on a TV as I could ask them how they did it.

About all I know is the person maybe rewound the deflection yoke of the TV they used.


Last edited by Tube Radio on Sep Wed 25, 2019 8:57 pm, edited 1 time in total.

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 Post subject: Re: Sony TV to scope clock
PostPosted: Sep Wed 25, 2019 4:01 am 
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I found on the board where that point is which thankfully was connected to another point only by a wire.

I removed it and connected the video output of a VGA to composite converter and here's what I got.

Attachment:
Sony TV.png
Sony TV.png [ 800.62 KiB | Viewed 1510 times ]


Now it's by no means perfect and I know there's a few issues as I originally only replaced the bad electrolytic caps on the deflection board and once I replace the others the picture should be much better.

Also the trimpots need to be cleaned.

What I did so I wouldn't have a wire hanging out the back and so I wouldn't have to hack the case is to wire the speaker directly to the audio output and use the headphone jack for the video input.

I do have one question.

Is there a way to adjust the horizontal width or would doing so also affect the HV from the flyback?

I'm not liking the overscan it has.

The only place I see where I could possibly adjust the horizontal width is the secondary of the horizontal drive transformer with the potential point shown in red. Now will that work or will it adversely affect the circuit?

Attachment:
Horizontal.png
Horizontal.png [ 53.62 KiB | Viewed 1510 times ]


The idea is I want the whole picture on the CRT. Doesn't matter to me if the full CRT face isn't filled so long as I see the whole picture.

The only issue I could possibly see is that a decrease in horizontal width means the signal is lower in amplitude which would mean less signal feeding the flyback meaning less HV for the CRT.

This is basically something I'm playing around with.

Serves no real purpose yet other than to prove it can display a composite video signal.

Ultimately if I find a reasonable way to convert the X Y Z signal into composite video, I'll use this as a scope clock display.

EDIT:

Here's a picture after the last few original electrolytic caps on the deflection board were replaced. I also replaced some other questionable ones I had used several years ago when I first got the TV as I think they were what I had on hand or pulled from defunct devices.

Attachment:
Sony TV 2.png
Sony TV 2.png [ 812.01 KiB | Viewed 1487 times ]


I did find where I can cut a trace and add a resistor to try and reduce the horizontal size.

Also I discovered that the issue I was having with my composite video to X/Y/Z converter making the picture darker as more white was being displayed isn't an issue with the circuit at all, but is most likely the VGA to composite converter I used given I have the same issue here and that converter is the common denominator.

Also I discovered that this TV will sync a pal composite video signal with a slight readjustment of the vertical hold control and I would have to adjust the vertical size some.

Overall I am satisfied that it at least displays a picture that is at least nearly as good as a composite video signal which is all I ever expected it to do.

I do plan on firing it up on the internal power supply instead of the regulated 12 volt supply I'm using so that I can see what the B+ voltage is.

I seem to remember the TV working better on an external supply and that could perhaps be because either the original filter caps are going bad, it uses a selenium rectifier or both.

I do know the B+ listed on the schematic is 12Vdc so I may replace the selenium with diodes then use a 7812 after the choke or perhaps I won't even need the choke then with the 7812.

Still has a slight horizontal issue though which could be a resistor out of tolerance or maybe a cap issue.

Attachment:
Picture.png
Picture.png [ 679.5 KiB | Viewed 1487 times ]


Far as making it into a scope clock display I am thinking that I'll put that idea aside for now.

EDIT:

If I disconnect the horizontal deflection coil I get a solid vertical line as expected, but it looks like it is off center to the left and I see no way to adjust that.

Attachment:
Horizontal.png
Horizontal.png [ 756.47 KiB | Viewed 1456 times ]


Now if I place a 4.7 ohm resistor in series with the horizontal deflection yoke I get this. The display seems to only reduce the horizontal size on the right

Attachment:
Horizontal 2.png
Horizontal 2.png [ 809.71 KiB | Viewed 1456 times ]


Also seen in that picture is a black vertical line on the right side of the screen which does not go away.

Now if I set the bright and contrast right so that I get a good picture without the raster showing, that line isn't there.

Looks like I may insert a resistor in the secondary of the horizontal drive transistor and see what that does.

If all else fails I'll put it back together and use it as a display as is.


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 Post subject: Re: Sony TV external video input mod
PostPosted: Sep Sat 28, 2019 2:09 am 
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Nice going so far!
Thot I'd respond in a positive manner, knowing zilch about TV except what I glean from threads like this. 8)

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 Post subject: Re: Sony TV external video input mod
PostPosted: Sep Sat 28, 2019 2:16 am 
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Location: Texas, U.S.A.
Excellent work hacking into that TV, TR.
I like it, very encouraging.

...


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 Post subject: Re: Sony TV external video input mod
PostPosted: Sep Sat 28, 2019 3:34 am 
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Location: Warner Robins, GA
Thanks.

It gives an otherwise useless TV some sort of use.

Originally I had the plan of tapping the sync and video signals to feed a couple scopes to display a picture on an oscope, but the analog to digital transition messed that idea up so it sat for around 10 years until I wanted a larger screen for an oscope clock at work.

Wasn't sure how the deflection circuitry would work with the clock output so that's when I thought of doing the video mod as I had figured I could convert XYZ to composite which is actually no easy task.

So I decided to still do the video mod as it would give the TV some potential use.

The issue I think now is either the composite signal is just not that good or the VGA to composite converter isn't very good.

I'm almost at the point where the TV is operating well enough to where I may try feeding external vertical and horizontal signals to the deflection amps from a scope clock board just to see how the display looks.

The vertical is easy as there's a cap coupling the oscillator to the amp so I'll disconnect the cap from the oscillator side then apply the vertical signal there.

I'll use my composite to XYZ converter with a splitter on the composite so the composite signal feeds both converters.

That way I'll have the same composite vertical signal so I can judge how well it looks.

Horizontal may be a bit harder though as it uses a transformer in the oscillator and is pretty much direct coupled until the horizontal drive transformer.

It will either work or it won't work, but if it don't work there's nothing lost as I can still feed a composite signal to it.

I've replaced most of the resistors on the deflection board and I've noticed a slight improvement.

Just did most of the rest today so I'll test it later and see how the picture looks.

I may also invest in a better VGA to composite converter unless they all work the same and will not produce a picture that looks any better.

EDIT:

Just tried the TV.

The other two times I replaced resistors I saw some slight improvement.

This last time I saw a bigger improvement.

I also noticed that before replacing the resistors the vertical and horizontal hold controls had a broad range before going out of sync, but now the range is much smaller and based on what I remember of adjusting CRT TVs, the controls may well be operating as they should.

Now I did have to string as much as four resistors together to get a particular value, but I doubt that much matters in this type of circuit.

I do notice occasionally the horizontal sync looks like it may be trying to go out of sync so perhaps I should replace the resistors on the sync board as well.

I did notice that the adjustment data does list a few resistors with the value selected based on a certain parameter and in those cases I just replaced the resistor with the same value as the one I removed so that the picture is at least as good as it was when it left the factory. Not sure why those weren't made to be trimpots unless those were things that were a set at the factory kind of thing and never should have to be changed under normal circumstances.

Attachment:
20190928_020824.jpg
20190928_020824.jpg [ 217.45 KiB | Viewed 1435 times ]


EDIT:

I removed B+ from the tuners and RF/IF board and initially the audio amp until I thought that I could maybe use the amp for an external audio input which is plugged into what was the external antenna jack.

What I don't quite get is with the selenium rectifiers B+ was around 10.5Vdc, but with the diodes it is 12.44Vdc at the moment, but is subject to go up or down by a few hundred millivolts due to line voltage variations.

The reason I don't get it is because I thought given the battery this was designed for is 12 volts, that the transformer voltage would be high enough to where the selenium rectifiers would produce 12.6 volts and I figured on having to add resistance or a regulator to drop the voltage to 12.6Vdc.

That said I have no clue how good the original filter caps are other than that there's 835mVac on the first filter cap and after the choke there's only 6.6mVac. The three can caps feel cool to the touch.

Now if I flip the switch to charge I get an unloaded B+ of 14.8Vdc which I'm sure drops down with the load of a charging battery.

EDIT:

While looking at the sync separator board I saw where the CRT does have a magnet to control horizontal position so given the TV produces a dot for a few seconds after being turned off I did that and adjusted the magnet until the dot was centered as best as I could get it.

Also I saw where I could use an S video cable using just the luma signal and get a better B/W picture. So I ordered a better VGA to composite and S video adapter along with a S video to dual RCA plug cable.

EDIT:

Forgot that my laptop has a S-video out connector so I just need the cable and not the adapter.


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 Post subject: Re: Sony TV external video input mod
PostPosted: Oct Tue 01, 2019 10:07 pm 
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Location: Warner Robins, GA
I do have a question about the AGC circuit that I don't quite understand.

Attachment:
Circuit.png
Circuit.png [ 67.5 KiB | Viewed 1388 times ]


Not sure what the winding on the flyback is used for unless it was to power the AGC circuit. Also it looks like there will be a variable DC voltage going to the sync circuit which is the voltage across the 330 ohm emitter resistor.

Looking at the original schematic shows how the sync circuit is connected.

I initially just directly connected the video input tot he point going to the sync/video circuits which put whatever DC is on the output of the converter at that point. The picture displayed fine.

Decided to cap couple it as with nothing connected there's DC voltage at that point and I didn't want to take the chance of damaging a source, although the voltage present there goes to nearly zero when a resistor is connected between there and ground. Also I didn't want any DC present from the source to potentially affect the display. Think I may have used a 330 ohm resistor to ground after a 100uF cap. Picture looked the exact same.

Also there were two diodes connected across where the video signal is input to the sync board with one going to B+ and one to ground both reverse biased. Looked to be factory, but is not in the schematic.

Also a few of the resistors in the sync circuit are different than the schematic. The one that jumps out at me is the schematic shows 1 meg, but mine had a 680K installed. Also a 56 ohm resistor was between the input to the sync circuit and the sync circuit. Plus the two diodes I mentioned.

My thought is that perhaps the service info I have is for an earlier version and they found there were issues with the sync circuit and the later version solved the issues.


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 Post subject: Re: Sony TV external video input mod
PostPosted: Oct Wed 02, 2019 5:10 am 
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Well then I do believe I am well satisfied with the results I got using the S video cable to dual RCA plugs.

Here's a photo. Incidentally it shows the info about the display settings for the S video jack.

Attachment:
20191001_232701.jpg
20191001_232701.jpg [ 211.83 KiB | Viewed 1375 times ]


As can be seen it shrinks the vertical some I assume to account for the overscan so that the display fits on the screen.

Don't know if it does it for the horizontal as it is still off the screen on the left and right edges.

If I could reduce the horizontal signal level some without affecting the geometry and CRT HV I might be able to get it right.

I had trouble getting it to recognize a display was connected to the S video jack until I decided to try a 75 ohm resistor (made up of a 33 and 39 ohm in series for 72 ohms) across the video input jack. I ditched the capacitor I was using to couple the signal to the circuit.

Found that the horizontal would now barely sync.

I tried shorting across the 56 ohm resistor in series with the signal from the video input (was there from the factory unless someone modded it later) and horizontal now syncs properly.

Works best with the desktop resolution set to 640X480 which as I recall is real close to the composite video resolution.

I do have a question about the active signal resolution though.

It says 2276 X 480.

Not sure how to interpret that far as a NTSC signal goes.


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 Post subject: Re: Sony TV external video input mod
PostPosted: Oct Mon 07, 2019 4:37 am 
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So playing around with the horizontal size I found:

1. Altering the signal level before the horizontal output transistor results in lower CRT HV.
2. Altering the signal level to the yoke only causes the right side of the image to get smaller. It is less pronounced with an inductor though.

So if I really wanted a smaller horizontal size I would need a VGA to S-video converter that allows the vertical and horizontal size to be adjusted. That would be in the territory of expensive most likely and is more than I really care to spend on this project.

Oh I'm well satisfied with it as is though, but it would be nice to be able to see the whole screen instead of the horizontal over-scanned a little to where the edges of the display are slightly off the CRT.

The vertical is easy. Just adjust the vertical size control.

I can see why the horizontal is harder though given the flyback is driven by the horizontal amp.


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