Amiga 4000 sound problem

[manicx]

Not very original eh? A problem with the sound in a A4000. Before I describe my problem, I need to type down my A4000 spec:

-A4000/040 Rev B/Buster 11
-16 Fast RAM
-3.1 ROMS
-2HDs using a buffered IDE interface + 1 CD drive 24x
-CV64/4MB
-Internal scandoubler (Arxon using the video exp.)

So, on to my problem now. A noise is coming out of the left speaker. The noise is
this (248 Kb). Before you start saying about the C433s I need to describe the history to my problem:

My Amiga was packed for sometime due to my military commitment. After the army, I found a wee flat in Athens but had no space to set up my A4k. So I had to take it out of a box and install it when I wanted to use it. This started about a year ago.

I was using an external EZ-VGA scandoubler before I buy the Arxon SD. The scandoubler was pusing a bit the left RCA socket but it was not something to worry about.

About 8-10 months ago, I started hearing that noise. It was not happening as soon as I booted but usually after some time (more than an hour anyway). I thought that it was the crappy speakers but it was not.

The noise was not coming up constantly. I could hear it for a few secs, then it was going away, then it was coming back and so on. Strangely enough, when I was moving the speaker cable and the RCA sockets, it seemed that the noise was going away.

About a month ago, the noise became very disturbing while playing Kick Off 2 with my pals. The next day I decided to connect it to my amplifier and get some real sound. I got pure noise instead. I can hear the sound but the noise is coming out too.

So, I took out the mobo, and checked the connectors. They look okay. I also used a cotton bud to clean some parts of the mobo and the sockets. Put it back and noise was not coming out in the beginning. After 30-45 minutes it started again. Bummer!  :-x

So, before I asked for your suggestions/recommendations, I would also like to say that the Amiga clock is always showing the same date when I boot: August 27/1999! The battery looks okay (although I noticed some white crap on both poles - I cleaned it and put some vaseline like we did in the good old days with car batteries). Anyway, I ordered a new battery and it will be with me any day now.

So, what do you think guys? Is this a dry capacitor? Is this a problem with a faulty RCA socket?A friend of mine told me that if it was a problem with a C433, it should have happened ages ago. What tests should I do?

Basically, I do not know where to start. I am not very keen with electronics, and there are no Amiga repair shops in Greece (I have the audio scematic though). I love me A4k more than any girlfriend I had today and I want it to remain fully functional.

[xeron]

My A4000 audio died in exactly the same way. It started making that exact noise in the left channel, but at the start it would only do it every now and then..

"*pop* cracklecracklecracklecracklecracklecrackle *pop*", but it started to do it more and more.

Now, the left channel just crackles like that all the time, and the actual Paula audio is very quiet.

I think it *is* the capacitor problem, but the surface mount caps used look quite difficult to replace to me :-(

[Framiga]

Hi  manicx

IIRC the left RCA female connector, has a mechanical switch inside.

Try to move a bit the male RCA during playback.

If the noise stops, could be a defective RCA connector or a lack GND welding.

All the above . . .if you are lucky :-)

Ciao

-edit- sorry, no switch inside the connector, anyway if it isn't a mechanical failure, faulty capacitor could be the problem (as already said by xeron)..

[Tomas]

I have heard that faulty psus cause a problem similar to this, noise on audio.

Btw welcome to forum

[manicx]

Thanks. Well, I always lived on the expectation that my miggy will never have problems. I did buy some backup hardware like a PSU but never a mobo. I will try my replacement PSU (original A4kD) and I will replace the battery first. If problem persists, I will try and take out the left RCA socket and replace it with a new one. Finally, I will try to replace the capacitors. I will start from easier and move to more difficult tasks. I have some friends who can help me, but I really hope to find a vacuum for the melted iron. This way I will be able to replace the faulty bits easy.

[manicx]

Just a wee question guys. Are these the two C433s? I think they are but need a second opinion just in case  :-D !

[Castellen]

It's hard to see from the photo, but check for corrosion around the base of those SMD electrolytics.  I've repaired many machines on which those capacitors have leaked, which causes corrosion of PCB tracks.
Look for discolouration around the capacitors, solder joints looking "tarnished" instead of smooth and shiny, and a fishy odour which is very strong when you heat the solder joints.

If this is the case, I'd suggest replacing all the SMD electrolytics in the machine, especially all the 22µF ones.  There is a couple behind the serial port to replace at the same time.
You'll probably find that some PCB tracks and vias have been corroded and will need repairing.

Find someone who is experienced with SMD soldering to replace the capacitors, as it would be easy to lift tracks and cause further damage if not done correctly.


As for your battery clock problem, check for open circuit tracks around data latch U177, which may require replacement as well.  You can get them from decent electronics suppliers, plus I keep a stock of them here if you get stuck.
If you need schematics on this, get them here:
http://amiga.serveftp.net

I'm planning to write some web pages on battery replacement and RTC repair very soon when I get some spare hours, so if all else fails, keep an eye on the above site

Anthony.

[manicx]

This is cool info. Thanks. I wonder why there are no more people like you living in Greece! I have to rely on friends who are competent with soldiering irons but have no idea about Amigas.

In any case, can I just email you? I may be able to get super-duper close-ups of my mobo and the capacitors. I may need some advice too. Thanks for your feedback...

[Framiga]

@ manicx

so . .locate the U403 chip (the small chip in the photo LM833).

Follow the line from pin n.1 (should have a dot on the chip) and from pin n. 7.

These pins are joint directly to the C433 (22uF-16 volt).

They are by-pass filters and could be in loss.

Download the A4000 schematics and see the Audio picture.

A4000-Schematics

Ciao

[Cass]

@manicx
I'd be glad to help you, but I'm abroad now. Meanwhile you can check this info for commodore repairs & spare parts:

http://www.amigathering.gr/lab/repairs.html

________
PORNSTARS GAUGE

[SilvrDrgn]

Not very original eh? A problem with the sound in a A4000.

Another possibility - check the wires in the main motherboard power connector.  See my last posting in this thread (at the bottom of the page) - http://www.amiga.org/forums/showthread.php?t=106

[Castellen]

@ manicx:
Sure, feel free to email me with any technical questions and I'll do my best to help.

I know electronics isn't everyone's speciality, but I should be able to get you most of the way if you're OK with a multi meter.
Unfortunately SMD soldering is a skill which you can't simply pick up after reading a book, so if you need to replace capacitors, ICs or do track repairs, then do find someone who can.  I've seen lots of "disasters" where people just hoe in with a big plumber's soldering iron to try replacing SMD ICs and stuff.  Not pretty!

If you need any discreet parts, capacitors, batteries, ICs, etc, then I can also help.

Have fun :-)
Anthony.

[manicx]

Cass, I phoned the commodore repair centre in Greece a while ago but had no luck. After posting the link, I thought: "What the hell, let's give it another shot". To my surprise, they answered the phone. The guy told me that they don't do Amiga repairs anymore but I insisted and I described him that the problem is not with Paula, but with the output. He will have a look in my amiga although he said it may take a while because he is very busy at the moment.

Anyway, I don't care how long it will take. All I want is a healthy Amiga and that's all. I prefer to be without an Amiga for a month than without an Amiga for the rest of my life....  :-)

[Framiga]

by manicx on 2003/10/6 12:42:19

Just a wee question guys. Are these the two C433s? I think they are but need a second opinion just in case

ermm! . . .i apologize with you for my wrong previous post.

Yes they are the 2 C433 polarized electrolitic capacitor (strange package).

I've read yesterday, to replace it, with 2 NOT polarized capacitors (22uF-35 volt).

Ciao

[Castellen]

@ manicx:
Great to hear you found an Amiga repair place in Greece.  Get them to fix the battery clock at the same time.
We don't have the luxury of anything like that in New Zealand!  It seems I'm unofficially the Amiga repair place for the country :-)

If you want it done faster, you could always send the motherboard here...
Would probably be a bit faster, but shipping would be the killer.  I would imagine something like US$20 each way??