When you switch it on, does it work normally aside from the very loud hum, or are you just getting a hum and nothing else?

Thanks J M,

I ran the monitor for several hours today and it passed all the tests.  I'll be using it for a gig on New Year's Eve.  If it survives that, it will become a permanent addition to my PA system.  I appreciate the time you took to help me out. The world needs more people like you.

Thank you J M Fahey for the advice.  I built the series lamp bulb limiter, cleaned up the boards, soldered in the new TDA7294, disconnected the speaker and flipped the switch.  The bulb lit up for about a half a second and then went very dim.  I hooked up the speaker wires to my oscilloscope and only got a few millivolts AC.  I decided it would be safe to hook up the speaker.  As a test, I connected a microphone to the XLR jack and turned everything back on.  The bulb flickered again and went very dim.  I got a nice, loud, clean signal with the mike and no hum.  :dbtu:  Awesome!  The only thing I haven't tried yet is running the monitor without the series lamp bulb limiter.  I'm assuming the surge when switching it on is normal.  Is there any reason you can think of why I shouldn't put it back together and try it out?

I just acquired a non-functional Fender 1270p Powered Monitor.  The TDA7294 was also fried; in fact pin 7 (+vs signal) was completely blown off.  The fuse was also blown.  I removed the chip and replaced the fuse.  I already have a replacement TDA7294.  There are no other physical signs of damage on the boards.  I decided to test the voltages on the traces to the TDA7294 first.  The + - vs power (across pins 13 and 15) measures 33v.  The voltage across the traces where pins 7 & 8 would be (+ - vs signal) is 72v.  I think that's within the max ratings for the chip, but I'm a little afraid to solder it in, as it was burned out at that spot.  I'm not an electrical engineer, just a hobbyist, so I'm not quite sure where to look for a possible voltage surge.  There's an 8 pin power supply connector between the power supply board and the amplifier chip board.  I'm getting some high readings there too, so I'm assuming the power supply board was at fault or some object just shorted out the chip and everything else is ok. Does anybody have a suggestion as to which parts are most likely to be causing this sort of problem?  I would appreciate it if somebody could tell me where I should logically start looking.

Update:  One of the 4700uf caps was bad, so I replaced it.  Now I have + and - 43v where pins 7 & 8 would be and + and - 17v where pins 13 & 15 would be.  That is exactly what the schematic shows and according to the TDA7294 datasheet the chip can handle a maximum of + - 50v.  The only thing that puzzles me is why the original IC was destroyed.  Does anybody have any idea?  I still haven't replaced the amplifier chip because I only have one of them.  I guess I'll wait a while for a reply before I risk it.