Purple hue when using RF or Composite or RGB Scart - VGA fine!

[stu232]

My A1200 gives a pinky/purple hue to it's output when I use the built-in RF modulator, composite or SCART, however if I connect the machine to my GBS8200 then output to VGA then the picture is perfect - no purpleness!

Does anyone know what might be wrong?

[stu232]

ok so it seems I'm lacking a green signal, but why is green present when using my GBS8200 using this lead?

Why isn't green being fed into the RF modulator, Composite socket or RGB Scart?

I have included an image of the wiring of my cable that I use to feed the signal to the GBS8200, which gives me a good clear untinted picture on any VGA monitor.

[Solo761]

I have similar issue with one of my A1200s. If I connect it directly to monitor (Dell U2311H, supports 15kHz) picture has extra purple hue. If I use RGB Scart picture is fine. VGA cable is also fine, my other A1200, A600 and A500 work fine with it.


Although it was at least 6 months since last I tried it and that was RGB to Scart -> Scart to HDMI adapter. Maybe it does something to the signal so it corrects it. I'll have to try it directly to TV now that I have one that can display Amiga picture through Scart.

[roy bates]

looking at the pictures,you might have a short between green and red.

[stu232]

@ Roy, that cable is fine mate, that's the one I use to feed the signal into the GBS8200 which gives me the perfect picture on my VGA monitors.

The problem is when I'm using an RGB Scart, RF or composite connection going directly to a CRT the picture has the purple hue.

So...

Amiga + GBS8200 + VGA = Perfect image.
Amiga + Any other type of connection = Purple picture.

I've tried it with 3 old CRT's, all CRT's give me the purple hue.
I've used the same RGB SCART cable on my A500 and the picture is perfect on the same CRT's.

[stu232]

Looks like things have gotten worse.

None of my CRT tv's can sync with the A1200 using either RF or Composite.

A1200 through GBS8200 to VGA is still perfect.

Here are some images....

[Stedy]

@stu232

Your cable is wrong.

Pin 9 has the yellow wire, that is digital blue, pin 10 has a grey wire, that is the composite sync signal. The TV may be blending the blue video fed to it?

For the GBS-8200/8220 add a 680 ohm resistor on the C-SYNC signal. For a SCART lead, add a 270 to 510 ohm resistor on the C-SYNC signal from pin 10 of the Amiga.

How many ground leads and to what pins are they connected?

Ian

[stu232]

Thanks for the reply Ian.

I seem to have confused everyone with the picture of the cable I posted. That is the cable that I use for VGA, it gives me a perfect picture when connected to the GBS8200 and any VGA monitor.

My problem is with my RGB Scart, RF and Composite output, the RF and Composite doesn't sync to my TV (it did last week but it doesn't now) and when it did the picture was tinted purple.

Using my RGB Scart lead I get a nice clear picture but it is purple.

See above images.

These same cables give me perfect images on all displays when I'm using my A500.

[Solo761]

GBS board has potentiometers for each of color lines, maybe it's ballanced that way monitor gets colors of same "strength" and it looks fine?

I just tried that A1200 I mentioned and it's off via scart. It seems HDMI adapter tried to balance the colors so it was less noticable.

This is the defective one

http://i.imgur.com/dilX9oG.jpg

and this is the good one

http://i.imgur.com/F27rvaf.jpg

I've just checked the colors in Paint Shop Pro and it seems that blue is cca half of what it should be. For example, in workbench arrow good one has blue component at 100-110, while on defective one it's 50-60. I think I'll have to disassemble if there's some kind of resistor added where it shouldn't be :/.

[stu232]

I rather like the green hue on your first image

[Solo761]

Maybe, but it's annoying . I checked all lines today, from video DAC to DB23 connector, every resistance was as it should be according to schematic. I even checked lines from LISA to DAC for every color and there were no problems. I guess that it means it's either LISA or BT101 DAC (VP101 in my case).

Now that I think about it, I think it worked like this from the start. But when I got it a while back I had it connected to an old CRT and it wasn't so noticable as on LCD. It also had problems with floppy drive. Every time it clicked picture would flicker, and if I inserted the floppy for "real" read it would garble and eventually froze with black screen. For a quick fix I made small adapter board to take 12V from floppy connector and make it 5V via LM7805 voltage regulator. This "fixed" it so floppy didn't freeze it. Today I found what was the problem. Somebody tried to "fix" it before. It had small tantalum capacitor over D215A and elco capacitor over D215. This usually fixes the flicker some A1200 have, but I don't think both are required. Plus elco was 47uF and it should be 1 - 4.7 uF. I removed them both and put 2.2uF elco over D215 (it goes from ground to voltage refrence pin on video DAC). Originally LM385 1.2V zener diode was supposed to go there, why they skipped it I don't know.

Without these capacitors picture was somewhat garbled, like bleeding, I forgot to take picture. With just this 2.2uF cap it's stable and floppy doesn't affect the picture any more. At least I got that sorted out.

Unfortunatelly I'm stuck as far as blue color goes. This is how kickstart screen looks

http://i.imgur.com/DHtjvRv.jpg

It works fine, it's just missing a lot of blue .


In your case I'm puzzled why it works fine via VGA port and not via SCART. Same connection is used. If only RF and composite were affected I would blame CXA1145 video encoder. Small chip below modulator box and capacitor forest , left of IDE connector. It's job is to convert RGB signal to composite and pass it on to modulator for RF. DB23 lines are directly from Video DAC chip.

[FOL]

Check the ceramic caps going to the sony chip. I had this issue recently and the hue turned out to be the cap on red line was short circuit.