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Old 19 May 2010, 14:15   #1
cosam
 
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A600: missing sound channels

I recently acquired an A600 which had a lot of static noise on both left and right audio outputs. Now the static is gone, but it would appear it took the second and third audio channels with it. (I know this because I messed around in OctaMED and the first and fourth channels were the only ones which worked.) As I can still get something on both left and right outputs, I'm thinking something broke inside Paula. Or am I overlooking a simper explanation?

Cheers,

Steve
 
Old 19 May 2010, 14:20   #2
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First check with a known working PSU, however it is probably a dead component in the computer this time.
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Old 19 May 2010, 14:59   #3
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Thanks, I'm pretty sure the PSU is OK but I have a couple of others I can try. I forgot to mention that there are a few leaky capacitors on the board which I was planning to replace anyway. I thought that these may be the cause of the static, but having two channels disappear while there's still output on both left and right audio makes me think it's something else.
 
Old 19 May 2010, 17:44   #4
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For what it's worth, I was having very similar audio problems with one of my A1200 boards and it turned out to be leaky caps. I removed 4 caps, cleaned up the board using fluxclene and put some new caps on, all perfect now.

I was getting dropouts on just one or two channels although sound was still coming out of both the L and R outputs - sometimes just a lot of bass missing from one channel, and occasionally some static.
All of these problems were solved with the cap replacement - if you know the caps are leaky, definitely change them before looking for other causes.

EDIT: If you can't see whether they're leaky or not, smell them! If anything smells fishy, replace the cap or at least clean the board round that area.
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Old 19 May 2010, 17:56   #5
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That sounds encouraging, thanks. It looks like there are two different makes of SMD electrolytics used on the board and all of one type have leaked quite noticeably, enough to tarnish the solder joints. I'll get them fixed first. Unfortunately, two of them are right between the keyboard connector and audio sockets so I'll probably need to desolder more than just the caps...
 
Old 19 May 2010, 20:31   #6
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Yeah, I know which caps you're talking about - it's a little tricky, but so long as you're not using a soldering iron the size of a spade it should be possible to remove them without having to desolder anything else.

BTW I just replaced them with ordinary (non-SMD) electrolytic radial 25V 22uF caps as I had them lying around, works fine. Good luck.
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Old 20 May 2010, 05:14   #7
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Yeah, I know which caps you're talking about - it's a little tricky, but so long as you're not using a soldering iron the size of a spade it should be possible to remove them without having to desolder anything else.

BTW I just replaced them with ordinary (non-SMD) electrolytic radial 25V 22uF caps as I had them lying around, works fine. Good luck.
I'm sure you used non polarised ones in the sound circuit, I bet they were also 22uF 16V. Certain caps in the sound circuit should be non polarised, signals can swing between the + / - 12 volt rails.

Advice is always a good thing, but making sure you replace the parts with the proper parts is also essential.
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Old 20 May 2010, 05:46   #8
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Quote:
Originally Posted by cosam View Post
I recently acquired an A600 which had a lot of static noise on both left and right audio outputs. Now the static is gone, but it would appear it took the second and third audio channels with it. (I know this because I messed around in OctaMED and the first and fourth channels were the only ones which worked.) As I can still get something on both left and right outputs, I'm thinking something broke inside Paula. Or am I overlooking a simper explanation?

Cheers,

Steve
Doesn't make sense. Channels 1 and 4 are left, 2 and 3 are right.
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Old 20 May 2010, 10:50   #9
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I'm sure you used non polarised ones in the sound circuit, I bet they were also 22uF 16V. Certain caps in the sound circuit should be non polarised, signals can swing between the + / - 12 volt rails.

Advice is always a good thing, but making sure you replace the parts with the proper parts is also essential.
Well, I can't speak for cosam, but all of the caps which had leaked on mine were polarised 22uF caps, hence why I replaced them with the same value ones.

I've seen differing opinions regarding using non-polarised caps for the audio circuitry - having read both sides of the argument, I came to the conclusion that I didn't care. If I have to replace the caps again at some point in the future, fine.
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Old 20 May 2010, 11:02   #10
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Well, I can't speak for cosam, but all of the caps which had leaked on mine were polarised 22uF caps, hence why I replaced them with the same value ones.

I've seen differing opinions regarding using non-polarised caps for the audio circuitry - having read both sides of the argument, I came to the conclusion that I didn't care. If I have to replace the caps again at some point in the future, fine.
There are no two sides, Commodore screwed it up in the first place, they should be non polarised.
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Old 20 May 2010, 12:24   #11
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Certain caps in the sound circuit should be non polarised, signals can swing between the + / - 12 volt rails.
Which are those, out of interest? All the caps I intend to replace are regular electrolytics.

Quote:
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Channels 1 and 4 are left, 2 and 3 are right.
Aha, that is good to know! I guess I (probably quite literally) have my wires crossed somewhere. It would definitely make much more sense, not to mention be easier to troubleshoot, if either left or right is missing completely.
 
Old 20 May 2010, 12:55   #12
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There are no two sides, Commodore screwed it up in the first place, they should be non polarised.
Well, some people say it's "essential" to replace the caps, while others say it may increase the chance of leakage in the future.
Since only one of my Amigas has suffered from this problem in well over 14 years, I'm happy to take the chance that I'll have to replace them again at some point. If I get another 10-20 years our of it, I won't complain!
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Old 20 May 2010, 13:04   #13
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Well, some people say it's "essential" to replace the caps, while others say it may increase the chance of leakage in the future.
Since only one of my Amigas has suffered from this problem in well over 14 years, I'm happy to take the chance that I'll have to replace them again at some point. If I get another 10-20 years our of it, I won't complain!
You're missing the point, replacing them is good, but with the right type is what's essential, else you perpetuate the problems.
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Old 20 May 2010, 13:24   #14
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You're missing the point, replacing them is good, but with the right type is what's essential, else you perpetuate the problems.
Well, we may have to agree to differ and leave it at that. Clearly your interpretation of the word "essential" is very different to mine.

Capacitors can leak for a number of reasons such as age, overheating, overvoltage, lack of use etc anyway.
There's nothing to say that a non-polarised cap isn't going to leak in the future, and IMHO the whole Amiga audio capacitor issue has been blown out of proportion.
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Old 20 May 2010, 13:35   #15
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There's nothing to say that a non-polarised cap isn't going to leak in the future
Yes there is. Electrolytics are the only caps that leak, no other type of capacitor uses a fluid.
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Old 20 May 2010, 14:03   #16
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Well, we may have to agree to differ and leave it at that. Clearly your interpretation of the word "essential" is very different to mine.

Capacitors can leak for a number of reasons such as age, overheating, overvoltage, lack of use etc anyway.
There's nothing to say that a non-polarised cap isn't going to leak in the future, and IMHO the whole Amiga audio capacitor issue has been blown out of proportion.
Tell that to the people whose corrosion I get to clean off their A4000 boards, predominantly from the 22uF 16V caps
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Old 20 May 2010, 14:05   #17
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Yes there is. Electrolytics are the only caps that leak, no other type of capacitor uses a fluid.
I think you're getting confused. Non-polarised and non-electrolytic caps are two separate things. It's entirely possible to get non-polarised electrolytic capacitors.
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Old 20 May 2010, 14:12   #18
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Tell that to the people whose corrosion I get to clean off their A4000 boards, predominantly from the 22uF 16V caps
I've had to replace leaky caps on my A4000 and my A1200, and not all of them were on the audio circuitry. I'm sure it's a common problem, but that's the nature of electrolytic caps.

It may well be ideal to replace a couple of the audio caps with non-polarised ones, but you telling me that having already replaced my leaky caps with polarised caps, it's *essential* that I replace them again with non-polarised caps? If so, that's what I'm disputing.
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Old 20 May 2010, 14:54   #19
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I've had to replace leaky caps on my A4000 and my A1200, and not all of them were on the audio circuitry. I'm sure it's a common problem, but that's the nature of electrolytic caps.

It may well be ideal to replace a couple of the audio caps with non-polarised ones, but you telling me that having already replaced my leaky caps with polarised caps, it's *essential* that I replace them again with non-polarised caps? If so, that's what I'm disputing.
Your board, you do with it what you will. Lower value electrolytics more commonly go bad, but not always that way. The ones under the most strain usually die first.
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Old 21 May 2010, 09:31   #20
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I think you're getting confused. Non-polarised and non-electrolytic caps are two separate things. It's entirely possible to get non-polarised electrolytic capacitors.
Bullshit. Show me one.
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