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-   -   Amiga 4000 Sound Problem (http://eab.abime.net/showthread.php?t=11266)

manicx 15 September 2003 10:57

Amiga 4000 Sound Problem
 
Okay guys, sad day for me. In the last few months, my Amiga 4000 was packed in the box due to lack of space in my wee flat. I was just taking it out when I wanted to do something with a real computer.

After a point I noticed some noise coming out of the speakers. In the beginning, this was very random and I always thought it may be the cheap speakers. On saturday, we had the Greek Championships in Kick Off 2 and my A4K was on for 7 hours. After a point the noise was constant and very disturbing. I decided to investigate the problem.

I noticed that the noise was also coming out through other speakers too of much higher quality. I took the mobo out, cleaned the sockets and the dust. Nothing, noise still there.

Here's what I hear:

http://users.hol.gr/~manicx/Downloads/noise.mp3

One thing that makes me feel suspicious is that I used to have an external scandoubler that was sqeezing the left audio port a bit. I am not sure if this noise is due to the dated RCA sockets. Sound is coming through the sound chip so I assume it is a problem with the output. I am not sure if this is due to RCAs or a capacitor.

Here's a picture of the right socket:

http://users.hol.gr/~manicx/Downloads/close.jpg

When I tried to insert a screwdriver in 1, I got the same noise. In 2, you see the CD audio output that mixes with the Amiga output. I took this off and noise is still there. The card you see on the top is a scan doubler and has a safe distance from everything else.

On a second test, I noticed that the noise is coming out from the left speaker. When I unplugged the left RCA socket, the noise passed to the right one. This is 80% certified test, I just leave 20% in doubt because I was a bit confused last night.

What do you think guys? Could this be a RCA socket problem? Is it a capacitor? Is it something else? What do you recommend me doing. I 'm feeling crap but I am prepared to fix that because I love my Amiga 4000. BTW, does anyone know where I can find the scematics of a Rev B A4000 motherboard. I found them only to (several) IFFs but I prefer a single image that I can print and take it to an electric engineer in case that my Amiga needs a surgery. Hope I didn't forget anything.

Severin 15 September 2003 14:03

Sounds like a dry capacitor to me, the 'unplug the left' test means nothing on an A4k, when only one lead is attached the output is automatically onverted to mono (for old monitors)....

now your mp3 has finished dl'ing.. it does sound like a capacitor...

manicx 15 September 2003 14:30

Thanks for your help. A friend of mine who is an electric engineer said that the most likely cause of this is a capacitor. I already made a cool picture of the scematics of A4k's audio. I am not sure though if the guy who is going to look after my mobo needs a full picture of the whole mobo or just the audio system. If anyone has a full image of the A4000 (Rev B) scematics, I would appreciate any help with it.

EDIT:

How safe is to do things with the A4k mobo? Is it safe to try to remove a capacitor (if it is a capacitor) or am I going to blew everything up?

Severin 15 September 2003 22:43

It shouldn't be too much of a problem as long as you have a decent soldering iron, 17w or thermostatically controlled to avoid excess heat dissipation through the MoBo, DON'T use a 15w iron, they just heat the MoBo up before the solder melts :(

Use a decent desolder tool, 'blob & bang' is not a good idea here :)


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