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Old 09 February 2018, 15:01   #1
hb129
 
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Amiga 500+ display problems - ghosting and vertical bands

Hi everyone,

Recently bought an A500+ from eBay and it's got an issue with the display output, both through the RF modulator and Composite.

There's a significant amount of distortion and ghosting, as well some vertical bands

I know battery leakage is a problem with this model and I'm going to open it up and check for corrosion and continuity as best as I can. It does appear to be functioning well apart from this display issue.

Are there any specific areas I should focus on after opening it up?

Kipper2k had a similar (but less severe) problem with his A600 here:
http://eab.abime.net/showthread.php?t=47782

It was suggested that a recap might be a good idea and then checking U12. Does anyone have any experience of a similar issue with the A500+? Can anyone help with some useful pointers?

Many thanks
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Old 09 February 2018, 15:56   #2
Akira
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The A500+ doesn't have capacitors like an A600, so you can't compare.
It could be the video decoder, but dunno. Try it with RGB and see what happens.
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Old 09 February 2018, 16:13   #3
Daedalus
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True, it's unlikely to be because of capacitors leaking and causing damage. But if the capacitors have dried out and aren't doing their jobs any more, you could be seeing electrical noise that could manifest itself like that. It could also be a poor ground connection somewhere, either the cable or on the PCB, so it's worth checking the ground continuity in the area. RF is particularly prone to ghosting - do you have any other cables to try? What does composite directly from the machine look like? It will be greyscale but might be free of the ghosting.
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Old 09 February 2018, 17:27   #4
pandy71
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It may be bad cable... looks like impedance mismatched.
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Old 09 February 2018, 17:31   #5
robinsonb5
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Quote:
Originally Posted by Daedalus View Post
What does composite directly from the machine look like? It will be greyscale but might be free of the ghosting.
Yes, definitely check that.

My guess would be this is a cracked solder joint or dried out capacitor in the A520 modulator somewhere, rather than in the Amiga itself.
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Old 09 February 2018, 19:03   #6
hb129
 
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Thanks to everyone who has replied.

I did check with the composite output and the image is very similar, ghosting and vertical bands, although obviously the display is in mono. I think that rules out a modulator or cable problem unless I'm missing something.

@Daedalus - when you mentioned to check ground continuity in the area, I'm assuming you mean in the RF area of the board. Is it possible that the grounding issue could also happen around the Denise and CIA?
 
Old 09 February 2018, 20:09   #7
Akira
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It could also be a PSU problem, I would check that too. It could well be the ground on it has a problem.
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Old 10 February 2018, 02:04   #8
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It's going to be a battery leak and corrosion on the legs of the video chip
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Old 10 February 2018, 03:00   #9
hb129
 
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Tried an alternate PSU and same issue. The battery corrosion hypothesis sounds like it could be very plausible, I'm going to have time to have a root around the mobo tomorrow so I guess I'll find out then.
 
Old 10 February 2018, 17:41   #10
hb129
 
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Yeah, looks like the battery has leaked causing corrosion to a number of caps and resistors, as well as the first couple of pins on U12

The item was listed as working so going to return it I think. The leak isn't as bad as some i've seen but there are probably at least 8 components that I'd need to replace and my desoldering skills are not the greatest

Thanks to everyone for the help
 
 


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