Yeah, I must have created it in the german area somehow. The diodes test ok with my multimeter, have taken the fets out too and tested and they seem ok with a basic MM test. The slightest touch on a ground point with the scope or meter can trigger the distortion. I'm back to my theory that it's feedback on the muting circuit, that the circuit is not muting because the processor isn't putting out high enough. I was thinking of ways to recreate the signal. The record out signal is inverted, so it's low when playing and high when recording but the muting circuit is reversed. Do you think I could use some sort of small logic gate IC to pickup this signal and split it, inverting it for the record mute and passing through for record out? It must be able to pull it low somehow. The thing I notice is that at the connector I pickup +5.1v high and -2v low, looking at the circuit diagram it seems to connect to the negative 8v rail via a 10k resistor.