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Old 13 June 2017, 08:20   #1
skoopi
 
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Hooooo Amiga 600 video trouble

Hi everyone.
I am new here. I hope someone can help me resurecting an old broken A600 I bought as 'parts' for a dime. It's a PAL version.
My skill concerning electronics are average. I am not a pro. I have no scope, just basic stuff.
The initial situation was that the A600 booted but has no video sync. in the RGB output. The composite worked only when I plugged into my capture card when I set it to a strange PAL/60Hz mode. (or in NTSC but then it was b&w).

A few pins in the RGB port where bended (same thing in the Pcmcia port). The machine has had a bad times.

I tested the resistors around the RGB port and found R251 was burned out.
I soldered a new one and managed to get a picture thru the RGB port using a GBS8200 RGV2VGA converter. (I have no TV set)

R251 is in the Hsync line. I think a previous user shorter the 12V pin with the Hsync pin (they are very close) and the resistor acted like a fuse.

The picture is not perfect thought. The bottom lines are trash. At least the A600 is usable, and I can manage that by adjusting the overscan to avoid using the trashed lines.

I cant figure out what's going on. Seems like the number of lines is similar to an NTSC picture even thow this is a PAL model.

The 'PAL goodies' section of the motherboard is populated all right.

By the way, I later changed all electrolytic capacitors and removed the TV modulator in order to install an HDMI output (bought a Vampire2).

So ultimatly I will use HDMI, but I vould like to fix the RBG output anyway.

Some help will be greatly appreciated.

Skoopi.
 
Old 13 June 2017, 10:01   #2
Daedalus
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The PAL models, when set to an NTSC screenmode, will have the same number of lines as an NTSC model. The only real difference is the colour encoding on the composite output, on RGB it will simply be 640x400 @ 60Hz instead of 640x512 @ 50Hz. Perhaps this is the issue from your converter - have you tried that with a PAL-format screenmode? An image of the problem might help to figure out what is going on as well.
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Old 13 June 2017, 12:16   #3
skoopi
 
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Pal mode

Yes, but everything is set to PAL.

In fact when I try NTSC Modes my monitor goes "No signal" and the capture card of my PC runs out of sync.

Here is a capture of the screen in HiRes PAL with the bottom lines going crazy.
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Old 13 June 2017, 16:50   #4
Daedalus
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Hmmm, I don't know so. Are you getting the same effect on RGB and on composite out?
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Old 13 June 2017, 19:17   #5
talybont
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I would try to find a way to view the signal without the GBS8200, to make sure you are not actually troubleshooting that thing and not your Amiga.
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Old 15 June 2017, 21:41   #6
skoopi
 
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I can see the composite output with my video HD projector (it's upscaling so it's not direct shoot) or using the capture card of my PC.

I can only see the RGB using the RGB2VGA adapter.

Both signals show garbage at the bottom of the image, but there are also strange vertical stripes on some colors on the video projector. I have no crt TV for years now.

My guess is that the video chip or the pal sync ocillator circuit are gone bad.

I have bought a brand new Sony chip to replace the video encoder but I am not very used to unsolder tiny surface mount chips. So I would prefer to avoid doing it just to see if it's the cause of the trouble.
 
 


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