Something is definately wrong here. The test tone should be 1khz and played on all four channels. My MBFM is in my workshop and I'm going away for vacation for a week so I can't record the test tune, but tyr google for 1khz test tune and you will know what it'll sound like. Have you checked, double checked and tripple checked every connection between the core->opl3 module->psu against the wiring diagrams? Have you checked for any soldering problems on the opl3 board? /offe