The TL494CN is a fairly prehistoric controller chip, and was never really intended to drive MOSFETs - it's from the bipolar era and has an NPN output transistor which makes a poor show of driving MOSFET gates. The little six-pin thing is likely, therefore, to be a MOSFET gate driver, something like this:
http://uk.farnell.com/diodes-inc/zxg...3-6/dp/1549141
Does the pinout match? Does the device have all 6 pins fitted? There are also quite a lot of gate drivers available in SOT23-5 packages, like this one:
http://www.ti.com/lit/ds/symlink/tps2818-ep.pdf
First thing to do is check whether the TL494 and driver have power or not. Check with a multimeter across the relevant pins shown on the chip data sheets. Be aware that all this stuff is on the primary side and therefore to be considered live, unless you're running the Beat Box from an isolating transformer.
If they have power, my next move would be to see what's coming out of the TL494. I'd use a scope for this, but with the Beat Box powered from an isolating transformer and the 0V rail on the primary side grounded. If you don't have an isolating transformer, don't try it! Failing that, voltage measurements from primary side 0V to the various pins on the TL494 might tell us something.
Circuits like this often have a startup arrangement involving a high-value resistor (100k-1M, usually) which goes open-circuit because it spends its life with nearly 300V across it. Sometimes there's a small electrolytic that's involved in startup, too, and those fail, occasionally with catastrophic consequences (cf some Samsung and Panasonic VCR power supplies).
Take care
Chris