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Old 14 January 2013, 22:14   #1
AlfaRomeo
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Joytech PS2 8" lcd to old computers

Hi,
I´m making some cables so I can connect my old computers to a Joytech PS2 8" Lcd.
Starting with my Spectrum +3 I made a RGB and a composite cables.
With the help of Photon I reach the stage of getting video from the +3 through RGB and composite in the LCD but with some garbage lines on screen (in composite and also in Rgb) like we could see in the 1st and 2nd attachments.
I connected a Spectrum 48K by composite signal and the image it´s clear like we can see in the 3rd attachment.
Also connected a malfunction +2 by Rgb made the garbage lines too (4th attachment).
So I conclude that something is different between the 48k video signal and the +2 and +3 video signals that made te garbage on lcd.
Could someone know what could cause and how to clear the garbage lines in the Lcd?
Thanks in advance.
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Last edited by AlfaRomeo; 14 January 2013 at 22:20.
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Old 14 January 2013, 22:57   #2
Stedy
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Hi,

Try adding 220uF capacitors, in series on the RGB signals. The video output of the Spectrum +3 is DC coupled. This value will be sufficient to pass the colour information through.

If the DC offset of the video is too high and the 8" panel has no AC coupling on the input, you will have problems, ahve seen this too often with LCD panels

Ian
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Old 14 January 2013, 23:29   #3
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Many thanks Ian, will try that solution.
Besides the DC coupled difference, could exist another differences between the composite video signals of 48K and +3?

Last edited by AlfaRomeo; 14 January 2013 at 23:34.
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Old 16 January 2013, 23:24   #4
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Quote:
Originally Posted by Stedy View Post
Try adding 220uF capacitors, in series on the RGB signals. The video output of the Spectrum +3 is DC coupled. This value will be sufficient to pass the colour information through.
Already tried the Stedy solution of adding 220uF capacitors in serie with the RGB signals but no notice of any differences on the displayed image

Any more ideas?
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Old 16 January 2013, 23:40   #5
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Maybe some informaton about the Spectrums video out is useful :-

http://www.fruitcake.plus.com/Sincla...SCARTCable.htm

Or maybe not :S
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Old 16 January 2013, 23:52   #6
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That extruded line on the second picture makes me wonder if something about the sync is messed up?

Are those errors fixed or do they flicker in random places?
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Old 18 January 2013, 17:29   #7
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would love see some pics of how you have connected it up and what the rgb wires are connected to, then I might get round to doing my 8" screen as well
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Old 18 January 2013, 21:24   #8
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Hi,

On the Spectrum +3, disconnect R41 (150 Ohm resistor). The 75 Ohm resistor inside the LCD panel, will be in parallel with R41 inside the Spectrum +3, giving a combined terminating resistor of 50 ohms. The sync output voltage will drop from 1.2V to 0.48V. This may be too small a signal for the LCD panel to lock onto and sync strip.

It looks like the Spectrum 48K has a 75 ohm output impedance with a standard 1.2V signal, which could explain why the 48K works better.

Good luck.

Ian
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Old 19 January 2013, 10:49   #9
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Quote:
Originally Posted by demolition View Post
That extruded line on the second picture makes me wonder if something about the sync is messed up?

Are those errors fixed or do they flicker in random places?
In the +3 initial menu screen, if I switch to another video input and then back to rgb input again, sometimes, these lines jump about 1cm above, and, if I keep switching between other inputs and rgb, eventually they back to original position again.
But they only jump between these two positions, the lines don´t jump to other positions besides these 2.
In screen with movement, eventually, the lines make some drag video artifacts as can be seen in the +2 photo (black with strips).

Tomorrow will try to remove the +3 R41 as Stedy says
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Old 20 January 2013, 16:37   #10
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Quote:
Originally Posted by Stedy View Post

On the Spectrum +3, disconnect R41 (150 Ohm resistor).
Already did that and the garbage lines in the image keeps the same

Quote:
Originally Posted by demolition View Post
That extruded line on the second picture makes me wonder if something about the sync is messed up?

Are those errors fixed or do they flicker in random places?
After a deeper study my conclusion is that when I start the +3 the image is like in the photo Spectrum7 and after swith monitor Off/On or jump between monitor inputs and then back to RGB again the image that appears is like the photo Spectrum8.
The garbage lines vary only between that 2 positions.
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Old 21 January 2013, 16:36   #11
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could you try with another +3 PSU? sometimes it can cause bad picture.
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Old 24 January 2013, 01:05   #12
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The problem is that I have only one PSU but already measured the +5v,-12v and +12v in the PSU and all seems ok.
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Old 25 January 2013, 22:54   #13
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Try this
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Old 28 January 2013, 02:01   #14
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maybe the problem is in inverted composite sync signal (why the hell did they invert it?). even though tv only uses phase. can you try amstrad cpc or some console which also has inverted CSYNC?
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Old 20 February 2013, 17:41   #15
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Quote:
Originally Posted by orange View Post
maybe the problem is in inverted composite sync signal (why the hell did they invert it?). even though tv only uses phase. can you try amstrad cpc or some console which also has inverted CSYNC?
Already tried Spectrum 48k (composite video), Timex Sinclair 2068 (composite video) and Amiga 600 (RGB) and all give a clear image without any garbage lines.
Does any of these computers have inverted CSync??
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Old 29 November 2013, 17:37   #16
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So did this experiment ever work out for +3 ?
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