Amiga 600 sound problems...

[ruireispt]

Hi guys I have an extra Amiga 600 HD which has some sound issues... Well the sound seems low on one stereo channel and the other one is really high and distorted. I already recapped most of the system except for a couple of caps near the PCMCIA slot. The sound chip heats a bit more than I expected but a friend told me that the high temperature on that chip is normal. Any ideas here? And if the sound chip is damaged how hard is for me to get a replacement?

Thanks in advance

 

[thgill]

If you have already recapped the board, I would also look at the power supply.

Much of the sound section is driven by the -12v rail on the psu. Make sure it's up to spec.

edit: You mentioned not replacing some of the caps near the PCMCIA port. I would replace those as well.

 

[demolition]

When the sound is bad in an Amiga it is usually not directly because of the bad caps, but indirectly as the leakage of the caps can have corroded tracks away.
Look at the schematic and check the connections and components from the audio connectors towards the opamp. You will probably find a bad connection somewhere here.

Also check the voltage of AVref, it should be around 2.5V. If it is <2V something is also wrong in this circuit, which will cause distortion.

 

[ruireispt]

Hi guys thanks for your answers

The old capacitors weren't leaking at all I just replaced them by intuition... I'll replace the rest of them and check voltage. I tried with different PSU and the result was the same... I really hope that the sound chip isn't damaged

 

[ruireispt]

Ok recapped the rest and checked voltage... No luck! Sound is very high and distorted...icard

 

[demolition]

I doubt that Paula is broken, as that doesn't normally happen. If the AVref voltage is fine then check all connections in the audio part of the schematic. There aren't that many components. If you still can't find any problems, it is probably the opamp IC (which can be replaced by a compatible new one).

 

[ruireispt]

nice tip I'll look into it as soon as I get the time

Thanks

 

[jimbob]

You got the A600 schematics? Great searchable zoomable redraws are here -

http://www.amigawiki.org/doku.php?id=en:service:schematics

Paula page is most likely relevant to your problem. If you hear anything recognisable at all, Paula is likely fine. U15 is LF347 quad opamp, I can send you a spare if it turns out you need it but I think it might be some of its set up components rather than the chip. If the tests suggested above check out ok, (-12V is ok, Vref is ok). Take a close look at the feedback components for the channel which is loud and distorted.

Try a tracker or look for a sound test utility on aminet to check which channel is distorted and if the other one is actually too quiet or just normal compared to a broken channel.