Need help troubleshooting an amplifier...

[SimonB]

I have a Telex EV SonicXS 4.1 sound system for my computer and I have had it for about five years. I've had a problem with it working properly. I'll turn it on and it makes a loud noise like AM-radio for about a minute, then that noise goes away and the subwoofer doesn't work and the satellite speakers sound like they are missing the treble. Then there's the AM-radio noise again and then suddenly a pop and everything sounds great. At least that's the way it usually happens.

Well I took apart the subwoofer which houses all of the amplifiers and crossovers. There are five small boards that look like the individual amplifiers for each speaker. There is a burnt smell and the board is burnt around the leads of a big resistor. The color coding on the resistor comes to 68 ohms, and I tested the resistance with my digital multimeter and it says 69 ohms so it looks good.

I can't find schematics anywhere online for this system. Are there any additional troubleshooting steps you guys can recommend?

Here are a couple pics of the amp and the burnt area on the board:

[Andrew Eckhardt]

The picture shows a couple thermally worked solder joints for some signal resistors going by that over powered power resistor. The power resistor is fine, but retouching all those solder joints would be step one.

[c2cthomas]

Seems that you have done the 1st thing which is a good visual check of things.
For something that is a thermal intermittent like this a shot of freeze spray Parts-Express.com:*ECG RX100-10 Antistatic Circuit Refrigerant 10 oz. | refrigerant freeze spray chiller chemical electronic chemicals in suspect areas can help to make the targeted component(s) act up. Some type of heat gun (hair dryer? don't let her catch you with it tho) to blow hot air can be helpful.

[redrooster]

i would change those electrolitic caps next to the burn mark as well they might have dried out a bit.