Colour problem over scart

pcut · 24 August 2009, 00:36

I was given an amiga 1200 recently and tried to connect it to my tv over composite video. The screen appeared red and slightly wavy from left to right. Tried the RF out socket and that was also tinged with red and wavy.

I thought there may be a problem with the whole rf circuitry so decided to try a scart cable. I have made one tonight (based on this: http://eab.abime.net/showthread.php?t=36602) and connected it up to my tv but without any resistors. The picture looks a bit clearer but it is still red and slighlty waving from side to side! Could this be caused by the resistor I never put in? Seems like a co-incidence with it having the same problem over composite.

Here is a pic of it plugged in through the scart i built:

and here is a pic from the composite video:

TheCorfiot · 24 August 2009, 11:51

Hey... Where's the Blue Output Gone !!!!!!!

I think you are missing the Blue signal and would need a scope at this point to check if the signal is being generated and / or being pulled down by the external circuitry, example the PAL encoder which is quite common to fail...

TC

pcut · 24 August 2009, 13:09

Ah yes looks like it is the blue that's missing. I dont have a scope, is there any other way I can check if blue is being generated? Is the pal encoder a chip on the motherboard?

TheCorfiot · 24 August 2009, 13:33

@pcut

The PAL encoder is the Sony CXA chip on the Mobo near the modulator, tbh faults like this need a scope to be able to pinpoint the issue and a good steady soldering hand...

Need to confirm all Blue Data is going into the Plessy DAC from LISA and that the Plessy Dac is producing the Analogue waveform.

TC

alexh · 24 August 2009, 13:35

It is more-likely a resistor or capacitor to have popped than a broken chip no?

TheCorfiot · 24 August 2009, 13:43

Quote:

Originally Posted by alexh

It is more-likely a resistor or capacitor to have popped than a broken chip no?

More than likely. but the CXA encoders can cause problems to the input circuit if they fail too.

I think you still need a scope to point you in the right direction even if the culprit turns out to be a cap or resistor...

changing components blindly can lead to more problems...

TC

Charlie · 24 August 2009, 14:04

I know this is probably a daft suggestion on many levels but as it's possible to pull S-Video directly out of the Sony CXA and one of our forum buddies does a lovely little add-on for just such a hack...

...good S-Video? - problem solved.
...red S-Video? - mobo is FUBAR, without the tools to test if properly.

Go on, flame me, it's a bit cold round here.

alexh · 24 August 2009, 14:11

You are flamed.

The two tests already tried, RGB SCART & Composite video should be good enough to prove that there is something wrong. There is no need to waste money on a S-Video amplifier board.

What is interesting is that there RGB screen does not look as it should if either G, B or both were not functioning. There is WHITE on the screen which is only possible if all three, RGB are working to some extent. Might be possible if you screwed up the cable and wired G & B together? Or perhaps it is just a side effect of having the contrast / brightness turned way up on your TV?

The composite screen looks more like you would imagine if some of the other colour components were low but not missing.

I made a few quick examples where I killed one or more of the colour component channels.

RED ONLY

RED + GREEN

RED + BLUE

pcut · 24 August 2009, 15:21

Thanks for the answers everyone, especially for going to the trouble of coming up with those pictures. It doesn't quite look like any of those though and the brightness is not overly high on the TV.

I am slightly more confused now as I have just tried the cable on an Amiga 500 and the colours are also messed up in just the same way! Maybe there is a problem with the cable and its just a co-incidence that its a similair fault to the composite out.

What is the purpose of the 1khom resistor on the 12v line, could that being missing cause this fault?

DH · 24 August 2009, 15:50

Maybe it is a problem with the cable, but it could also be the TV side. Have you tried something else in the TV scart/composite/RF sockets to make sure everything behaves correctly? D

EDIT: Actually, you've probably already tried and checked this, but it was only on the off chance the TV was solely being used for the Amiga

pcut · 24 August 2009, 15:55

Yeah the TV is fine, had to unplug a dreamcast from the scart socket to be able to plug the amiga in, so I know the socket is ok. It's not a very old tv either.

DH · 24 August 2009, 15:57

What make of TV?

pcut · 24 August 2009, 16:01

It's made by Orion, 32" LCD.

alexh · 24 August 2009, 16:49

Quote:

Originally Posted by pcut

Orion, 32" LCD.

From Aldi ?

alexh · 24 August 2009, 16:54

Quote:

Originally Posted by pcut

tried the cable on an Amiga 500 and the colours are also messed up in just the same way! Maybe there is a problem with the cable and its just a co-incidence that its a similair fault to the composite out.

Maybe. Do you have an A520 modulator you can try?

Quote:

Originally Posted by pcut

What is the purpose of the 1khom resistor on the 12v line, could that being missing cause this fault?

The purpose is to lower the +12v to be within the "RGB selection" input range of 1v-3v which signals to the TV to go into RGB mode.

http://en.wikipedia.org/wiki/SCART

If you are getting any sort of picture it is unlikely this is your problem (albeit not good practice, or safe!)

And while it doesn't really matter, 1K Ohm is the wrong resistor size!

http://eab.abime.net/showpost.php?p=573506&postcount=34

Also not shown in that diagram, you possibly want to connect SCART pins 5, 9, 13, 18 & 21 all to Video GND too!

DH · 24 August 2009, 16:57

Quote:

Originally Posted by pcut

It's made by Orion, 32" LCD.

There you go, that's your problem....... Shite TV

Sorry, couldn't resist

pcut · 24 August 2009, 17:33

Thanks for the help alexh, I don't have a modulator to test. I'll try connecting those pins to video ground and see if that helps. Also, on that diagram pins 16, 17, 18, 19 and 20 on the amiga side are all wired to scart video ground. Do you know if that is neccessary or would just one of these pins do the job?

alexh · 24 August 2009, 18:41

On the Amiga side, all of those pins are wired together on the motherboard. Effectively making them all the same. All you need is one wire soldered to any one of those pins.

At the SCART end, that one wire should to go to all the SCART video ground pins (daisy chain them all together using small sections of wire).

Audio ground should be separate.

Normally I would say not to be afraid to use too much heat when soldering, however take care when soldering a SCART plug not to overheat and melt the plastic or you'll end up with loose pins. Pre-tinning the ends of all your wires before you start will help.

pcut · 24 August 2009, 22:39

I've just soldered the video ground pins on the scart lead (pins 5, 9, 13 and 18) into the amiga ground and its still exactly the same. Hmmmm. Any ideas? Is this looking like a new motherboard will be required?

pcut · 24 November 2009, 23:50

I gave up on this for a while, but i think im gonna drag it out again and have another look at it.

After testing the scart lead that i made on an Amiga 500 I have, it has exactly the same problem so i think the issue may be the wiring of the scart, plus by co-incidence a faulty rf/composite on the a1200.

Need to try and figure out whats wrong wrong with the rf/composite...

24 August 2009, 00:36	#1
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	Colour problem over scart I was given an amiga 1200 recently and tried to connect it to my tv over composite video. The screen appeared red and slightly wavy from left to right. Tried the RF out socket and that was also tinged with red and wavy. I thought there may be a problem with the whole rf circuitry so decided to try a scart cable. I have made one tonight (based on this: http://eab.abime.net/showthread.php?t=36602) and connected it up to my tv but without any resistors. The picture looks a bit clearer but it is still red and slighlty waving from side to side! Could this be caused by the resistor I never put in? Seems like a co-incidence with it having the same problem over composite. Here is a pic of it plugged in through the scart i built: and here is a pic from the composite video:

24 August 2009, 14:11	#8
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,354	You are flamed. The two tests already tried, RGB SCART & Composite video should be good enough to prove that there is something wrong. There is no need to waste money on a S-Video amplifier board. What is interesting is that there RGB screen does not look as it should if either G, B or both were not functioning. There is WHITE on the screen which is only possible if all three, RGB are working to some extent. Might be possible if you screwed up the cable and wired G & B together? Or perhaps it is just a side effect of having the contrast / brightness turned way up on your TV? The composite screen looks more like you would imagine if some of the other colour components were low but not missing. I made a few quick examples where I killed one or more of the colour component channels. RED ONLY RED + GREEN RED + BLUE Last edited by alexh; 24 August 2009 at 14:34.

24 August 2009, 15:50	#10
DH Global Moderator Join Date: Sep 2008 Location: Might as well be WORK :( Age: 56 Posts: 4,110	Maybe it is a problem with the cable, but it could also be the TV side. Have you tried something else in the TV scart/composite/RF sockets to make sure everything behaves correctly? D EDIT: Actually, you've probably already tried and checked this, but it was only on the off chance the TV was solely being used for the Amiga Last edited by DH; 24 August 2009 at 15:56.

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24 August 2009, 11:51	#2
TheCorfiot Amibay Senior Staff Join Date: Feb 2008 Location: Cardiff / Wales Posts: 1,302	Hey... Where's the Blue Output Gone !!!!!!! I think you are missing the Blue signal and would need a scope at this point to check if the signal is being generated and / or being pulled down by the external circuitry, example the PAL encoder which is quite common to fail... TC

24 August 2009, 13:09	#3
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	Ah yes looks like it is the blue that's missing. I dont have a scope, is there any other way I can check if blue is being generated? Is the pal encoder a chip on the motherboard?

24 August 2009, 13:33	#4
TheCorfiot Amibay Senior Staff Join Date: Feb 2008 Location: Cardiff / Wales Posts: 1,302	@pcut The PAL encoder is the Sony CXA chip on the Mobo near the modulator, tbh faults like this need a scope to be able to pinpoint the issue and a good steady soldering hand... Need to confirm all Blue Data is going into the Plessy DAC from LISA and that the Plessy Dac is producing the Analogue waveform. TC

24 August 2009, 13:35	#5
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,354	It is more-likely a resistor or capacitor to have popped than a broken chip no?

24 August 2009, 14:04	#7
Charlie . . Mouse . . Join Date: Jun 2005 Location: Nowhere Age: 55 Posts: 1,792	I know this is probably a daft suggestion on many levels but as it's possible to pull S-Video directly out of the Sony CXA and one of our forum buddies does a lovely little add-on for just such a hack... ...good S-Video? - problem solved. ...red S-Video? - mobo is FUBAR, without the tools to test if properly. Go on, flame me, it's a bit cold round here.

24 August 2009, 15:21	#9
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	Thanks for the answers everyone, especially for going to the trouble of coming up with those pictures. It doesn't quite look like any of those though and the brightness is not overly high on the TV. I am slightly more confused now as I have just tried the cable on an Amiga 500 and the colours are also messed up in just the same way! Maybe there is a problem with the cable and its just a co-incidence that its a similair fault to the composite out. What is the purpose of the 1khom resistor on the 12v line, could that being missing cause this fault?

24 August 2009, 15:55	#11
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	Yeah the TV is fine, had to unplug a dreamcast from the scart socket to be able to plug the amiga in, so I know the socket is ok. It's not a very old tv either.

24 August 2009, 15:57	#12
DH Global Moderator Join Date: Sep 2008 Location: Might as well be WORK :( Age: 56 Posts: 4,110	What make of TV?

24 August 2009, 16:01	#13
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	It's made by Orion, 32" LCD.

24 August 2009, 17:33	#17
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	Thanks for the help alexh, I don't have a modulator to test. I'll try connecting those pins to video ground and see if that helps. Also, on that diagram pins 16, 17, 18, 19 and 20 on the amiga side are all wired to scart video ground. Do you know if that is neccessary or would just one of these pins do the job?

24 August 2009, 18:41	#18
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,354	On the Amiga side, all of those pins are wired together on the motherboard. Effectively making them all the same. All you need is one wire soldered to any one of those pins. At the SCART end, that one wire should to go to all the SCART video ground pins (daisy chain them all together using small sections of wire). Audio ground should be separate. Normally I would say not to be afraid to use too much heat when soldering, however take care when soldering a SCART plug not to overheat and melt the plastic or you'll end up with loose pins. Pre-tinning the ends of all your wires before you start will help.

24 August 2009, 22:39	#19
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	I've just soldered the video ground pins on the scart lead (pins 5, 9, 13 and 18) into the amiga ground and its still exactly the same. Hmmmm. Any ideas? Is this looking like a new motherboard will be required?

24 November 2009, 23:50	#20
pcut Registered User Join Date: Aug 2009 Location: Liverpool Posts: 26	I gave up on this for a while, but i think im gonna drag it out again and have another look at it. After testing the scart lead that i made on an Amiga 500 I have, it has exactly the same problem so i think the issue may be the wiring of the scart, plus by co-incidence a faulty rf/composite on the a1200. Need to try and figure out whats wrong wrong with the rf/composite...

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