"Secret" Overvoltage Protection?

I had an unusual experience last week, and figured I'd air it here for some opinions.

My Fly Baby had developed charging problems again. I wasn't sure if it was the generator or regulator, so I decided to do a bit of temporary wiring to bypass the regulator (Generator armature to +12V, ground the Field terminal).

I knew that in this mode, the generator could produce high voltages that could fry my radio (ICOM IC-A5) and transponder (Microair). So I left the power switches for both off.

I started the engine and watched the voltmeter. It read 8V at idle, but when the power came up, the voltage started to rise. I chopped the throttle before the voltage got much past 14V on the gauge.

So, the regulator was bad. Fortunately, I'd bought a spare at a fly-market a few years back ($5). I switched regulators, buttoned up the cowl, and mounted up for a test flight.

Strangely enough, neither the radio nor the transponder would power-up at first try. I cycled the power on and off, and pressed the "on" buttons on each a couple of times.

The ICOM powered up about the third try, and worked normally. The Microair was more stubborn, but after about 15 minutes of power-on, it too came on when I hit the switch.

The only thing I can think of is that both units have some sort of overvoltage protection that clears itself after a time. Neither has the classical "On" button with mechanical contacts that make or break the power to the unit; the "On" button undoubtedly tells some aspect of the circuit board what to do (on the Microair, one hits the power button multiple times to adjust the LCD lighting).

Still, the units shouldn't have seen that direct generator output...they were turned off. So what activated the overvoltage protection?

Anybody got any ideas?

Ron Wanttaja
.

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