Weak, fading Green signal on A600

Photon · 12 September 2013, 21:32

Day before I was going to bring my trusty, never-failing A600 Portable to a demoparty, it ... failed.

I had a look at it last days.

It fails with two cables and two screens, and is the same on composite as well.

I'll desolder my S-Video mod (which shows greyscale on all screens...), but I had a look at the diagram nad there seems no cap after the encoder, anyway.

Because this looks like a failed cap:

(This is DPaint drawing pure green tall narrow boxes, one big one with a hole in it with a smaller box inside. The green is very faint even at its brightest.)

At least it SEEMS to first charge the green and then discharge as the beam travels horizontally. It's not very visible in the photo, but it starts at a low intensity, goes to the highest in about 25 pixels, then fades sloowly down to black

Red and Blue are completely unaffected, and I see no horizontal fade or any hint of green for a white color, for example. It's pure Magenta all the way.

So my questions are:
1) IS this a bad cap
2) or could the S-Video mod (wires attached to Chroma/Luma on Denise)
3) If cap: caps should I look at? C211? I didn't see anything screaming out at me. Where is it on the mobo? (Damn, I should have checked revision before closing it again.)

Argh...Thankful for any help

roy bates · 12 September 2013, 22:44

have a look before the video encoder and after denise in that area.for rgb problems.

just a guess.

roy bates · 14 September 2013, 17:09

oh i forgot to mention,try to invest in a logic probe you may find it usefull for stuff like this.

alot cheaper than a osciloscope and a bit more cost effective on these jobs.

Loedown · 15 September 2013, 02:33

Set the screen for solid green ( fill with exactly the same colour ) and see what values you are getting on U31 2Y1 - 2Y4, they should be all unwavering high. Then follow the signal to Q212 and again check that it's holding the value without wavering.

12 September 2013, 21:32	#1
Photon Moderator Join Date: Nov 2004 Location: Eksjö / Sweden Posts: 5,604	Weak, fading Green signal on A600 Day before I was going to bring my trusty, never-failing A600 Portable to a demoparty, it ... failed. I had a look at it last days. It fails with two cables and two screens, and is the same on composite as well. I'll desolder my S-Video mod (which shows greyscale on all screens...), but I had a look at the diagram nad there seems no cap after the encoder, anyway. Because this looks like a failed cap: (This is DPaint drawing pure green tall narrow boxes, one big one with a hole in it with a smaller box inside. The green is very faint even at its brightest.) At least it SEEMS to first charge the green and then discharge as the beam travels horizontally. It's not very visible in the photo, but it starts at a low intensity, goes to the highest in about 25 pixels, then fades sloowly down to black Red and Blue are completely unaffected, and I see no horizontal fade or any hint of green for a white color, for example. It's pure Magenta all the way. So my questions are: 1) IS this a bad cap 2) or could the S-Video mod (wires attached to Chroma/Luma on Denise) 3) If cap: caps should I look at? C211? I didn't see anything screaming out at me. Where is it on the mobo? (Damn, I should have checked revision before closing it again.) Argh...Thankful for any help Last edited by Photon; 12 September 2013 at 23:36.

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12 September 2013, 22:44	#2
roy bates Registered User Join Date: Apr 2011 Location: birmingham Age: 55 Posts: 2,827	have a look before the video encoder and after denise in that area.for rgb problems. just a guess.

14 September 2013, 17:09	#3
roy bates Registered User Join Date: Apr 2011 Location: birmingham Age: 55 Posts: 2,827	oh i forgot to mention,try to invest in a logic probe you may find it usefull for stuff like this. alot cheaper than a osciloscope and a bit more cost effective on these jobs.

15 September 2013, 02:33	#4
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	Set the screen for solid green ( fill with exactly the same colour ) and see what values you are getting on U31 2Y1 - 2Y4, they should be all unwavering high. Then follow the signal to Q212 and again check that it's holding the value without wavering.

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