Help! Marshal MG50DFX Anybody Anyideas

[thomas7037]

My marshal amp recently stopped working so I decide to fix it. I replaced the main amp chip a TDA 7293 along with all of the other pre amp chip including many TL027`s when I put the amp on now it works all of the time but is very quiet? Can anybody shed light on my problems? I also noticed two leds in the amp one green and one red, are they for test purposes? should they light up?
Cheers for any help offered

 

[Enzo]

Look at pin 4 of the module ribbon, or pin 9 of the 7293 itself. This is the standby pin. There should be a positive voltage there - maybe 3-5v or something. When the big chip fails sometimes it damages the mute circuit.

On the main board somewhere is a small transistor and a zener that control this line. Shorted zener will leave the chip muted.

Something to check.