I've been running an Amp 7 for a few years with no problem but the Amp has stopped working. I've checked all the voltages and have a good clean 5v, 10v and 45v supply with no fuses blown. The mute LED lights up briefly and intermittently when switching the mute on and off but does not remain on when mute and there is no sound when the mute is turned off. How likely s it that the chip has gone and can I replace it? (It looks like a push fit chip - TA 3020). Is there anything else I should be looking for?