A2320 problems

[system11]

Hi all, I recently put my A2000 back into service, unfortunately when I turned it off a decade ago I didn't know about the battery problem... Anyway, that's all fixed.

The A2320 though has some kind of output problem - I don't recall if it was always like this, but I'm getting banding which specifically affects some shades of certain colours more than others. Additionally some artifacting along the leading edge of the 'bands'. Here's what I mean:



You can see top right banding on the dark brown, but the worrying one is on the top left - faint red stripes which only affect certain colours. For reference this was captured over the normal monitor output, you can see a whole area of shading is more or less missing on the first image where the red artifacts are.



Separately the normal monitor output seems to be a little strong on red and a little weak on green - are there known analogue components I should be checking? Machines is a rev 6 A2000.

If anyone can offer any advice I'd be grateful - my intent was to feed a TV with the normal monitor out, and feed a capture system with the scandoubled/deinterlaced output.

[MartinW]

The banding suggests that the PLL fine tuning needs to be adjusted. On the A2320 this is the fine tune adjustment on the back exterior of the card.

[system11]

Oh believe me I've tried that, both fine and coarse adjustment! Followed the manual to the letter.

[MartinW]

What monitor are you using? I've quite literally just been through this with my system because the banding was getting on my tits. It was really bad. It's taken me probably the last 3 hours of swapping monitors and getting the adjustment as best I could on each and I've finally got it so that the banding is more or less gone. Not 100%, but way better than it was.

The current monitor is an LG23" LCD TV. I know full well that if I plug this into my 17" VGA CRT and repeat the process the banding will be completely gone. None of the LCDs that I have will completely cope with the scan doubled image but what I have now is pretty good.

My Amiga doesn't have an A2320 incidentally, it is basically custom built / designed but it has the identical circuitry to the A2320 on the motherboard and the adjustment procedure and symptoms are identical.

If I was going to suspect anything then I might be tempted to replace the coarse adjustment capacitor but that's more because I'm not 100% positive I used the right value when I built the system. Something else that I'd consider is the monitor cable. I guess that can be a source of signal noise as well.

[system11]

I tried it on a VGA capture card, a Sony Bravia (lcd), and a Samsung PC monitor and they all showed the same banding but perhaps more worrying the same strange red stripy artefacts. The really strange thing about it is that it affects certain shades more than others, so for example in a light source to vector demo as faces turned they would suddenly appear to have very obvious striping.

I've been trying to find another one so I can compare, tthe only local owners I know of are the Cambridge computer Museum and they neglected to return my email, I was asking if I could bring my card and try it in their machine.