Ashdown EVOIII 500 Head - Constantly muted

[nove]

Hi all,

My Ashdown is playing up again. I've had this problem before and had it repaired, but my last repair tech is no longer in business and I'd like to try to solve this myself.

Simply put, the amplifier appears as though it's always muted, whether the mute switch is in or not. When I play a note, the note is audible (barely, like when muted), and its volume is effected (hardly, but still effected) by changing the input gain, but uneffected when changing the output gain.

I also sent a 1kHz tone through the amp, and found each mod stage of the amp (EQ, valve drive, sub harmonic etc.) all worked normally by effecting the tone, but again, nothing happens when the output is changed.

In short, there is no difference in volume between the mute switch being IN or OUT.

Can anyone help? I am not afraid to dig in, the amp is already in parts on my workbench.

Thanks,

Nick.

[Enzo]

But the power amp doesn;t realy have a mute, does it?

I don't have the III drawing handy, but if the II is sumular, there is a speaker relay. If yours has one, when power is on, measure resistance from the amp side to the output jack side for continuity. Well, make sure the relay energizes first.

With test signal applied to the input and controls up, scope the input to the power amp. Signal there?

You have either FX loop jacks or a pair marked preamp out and power amp in? Patch from send to return with a spare cord on either pair. ANy help?

If either of those jack sets exost, applu signal to the FX return or the power amp in. ANy output? Likewise feeding the test signal to the input, use another amp to monitor the FX send or preamp out - signal present?