Speaker Failure

[thunderdome2001]

I work at a studio that has a speaker selection of Yamaha NS10's (near field) and Tannoy (mains). The console is a Trident 24 using an external power amp for speakers. The power amp feeds to another external device (A/B switch between the speakers). It had collected a substantial amount of dust and need to be cleaned. The power for all devices were "Off" during detail. Power "On" and theA/B switch performs its task successfully but now we completely lost the "High" end for the mains only. Does anybody have any suggestions on where I should start. Thanks, Rob

[DAS]

You mean you've lost the high end for both pair of speakers? I'd start by taking the A-B box out of the signal path and see what happens.