This exact problem was fixed on my A4000D motherboard over the weekend!! The capacitors on my board have been replaced by the non-polarized type. However, upon putting everything back together, the sound on my A4000 was still terrible (the same as it was prior to the capacitor replacement). After 7.5 hours of messing around with the hardware (different motherboard, accelerator, removing expansion cards, removing Zorro expansion daughter board), my dealer and I found the problem with the help of his son's girlfriend (she works on electronic stuff all the time). It was as simple as the -12 volt and its associated ground wire not making proper contact in the main 6-pin motherboard power connector. Prior to the capacitor change, I had done some other work on my A4000T. In the process of putting it back together after that work, the -12 volt line and its associated ground wire got pushed out of the connector somehow so they weren't making good contact in the main power connector for the motherboard. The op-amps (operational amplifiers) that produce sound on the Amiga require both +12 volt and -12 volt lines and their associated grounds in order to function properly. Without either one, the sound output is very bad because they are unable to generate full waveforms. We connected the main power connector and then wiggled and pushed in all of the wires with a pair of needle-nosed pliers. After that, perfect sound from my system!
