The other day when I tried to power-up my MFJ-492X memory keyer, all I got was a short, low frequency “bzzz”. The lights down the left side of the front panel cycled as normal, but it wouldn’t generate any tones.
In the process of tracking down any power issues (including the internal 9V battery), I discovered the 3V Lithium battery (CR2430) had gone flat (0.0V). After replacing it (I had stuck a spare to the top inside of the box), at power-up, the unit would only give a long (4-5 second) “bzzzt”. Trying the (factory) reset procedure in the manual (holding the menu button down while powering-up) made no difference.
Going through the “usual” suspects, re-seating all the chips & connectors, didn’t work either. So I fired off a quick email to MFJ, and within hours, the answer appeared:
Hold down all 6 buttons while turning the power on (a bit tricky).
At this point the sweet “dash-dash-dash dash-dot” (ON) enunciated clearly, and things have been fine ever since.
Kudos to MFJ for their customer support; the unit is only 20+ years old 😉