Ok....Im pretty good working on airplanes as a wanna be A&P.....my son has a very nice 1976 Cessna 150M, low time, etc etc...the problem is the tail beacon quit....didnt notice it right away, but now will not come on.....however, when you turn the beacon switch off or the master switch off, the beacon will Flash ONE TIME. I have replaced the bulb, the switch, the transformer. Plugged the bulb directly into the transformer to isolate the tail wiring and I get the same result. I just can't figure out why the bulb will flash once when you turn the power OFF.....anyone???

thx Rick

By transformer, I assume you mean the solid state flasher (it's not a power supply in the tradition of a strobe) located in the tail? If you've got a constant 12 volts at the connector coming from the panel switch back to the flasher, and you've seen the bulb actually light up so you know it's not a burned out bulb, then the only thing left to fix is the flasher itself or the wiring between flasher and beacon. Did the original "transformer" that you replaced exhibit the same flash once behavior or was all just plain dead? My bet is you bought a dying flasher to replace your dead flasher. There is also a resistor in line between the flasher and the beacon that's supposed to eliminate the pulsing effect on cabin lights. Not sure if that could cause your problem.

I got lucky buying a working used one on ebay. The seller had about 6 of them and I asked for the one with the highest serial number.

I’ve already replaced the Whelen power supply. Does the same thing with the new one.

I don't believe Whelen makes the flasher for the tail beacon. The Cessna part number is C594502-0102 and it looks like:



Perhaps it's the resistor behind the flasher in the tail cone.

This is what’s in there

Ok, this is not just a "transformer" per say, but a high voltage power supply with a trigger circuit.

When energized, an internal oscillator, which you can often hear as a high pitched ascending squeal, steps up the battery voltage to about 400 volts DC thru a toroidal transformer and rectifier. This should appear on the Red (+Anode) and Black (-Cathode) wires. There is also a timing circuit which charges up a small capacitor from that 400 volt supply and then dumps that charge onto the White (Trigger) wire, via an SCR, thru a small trigger transformer in the base of the flash tube, sending a HV pulse onto the fine wire coil around the flash tube, causing it to discharge and flash. This repeats every second or so.

If your flash tube is only flashing once when you turn it on, that suggests that the timing circuit in the power supply is faulty and a transient, caused by turning it off, is firing the trigger. I can't offer you any way to test your trigger circuit. The fact that it flashes at all leads me to believe the HV supply section is working. A DVM can verify that for sure, just be careful at 400 VDC can be potentially lethal.

Other than testing your flash tube on another plane with a known working strobe or borrowing a known good strobe tube and trying it with your power supply I can't offer any additional advice. Check your ground and power to the supply, at the supply connector to make sure your getting the full battery voltage when operating. You could have some stray resistance in either the ground or supply lead preventing the supply from reaching its full voltage, reaching the firing threshold and triggering.

One more thing. Don't handle the glass on the flash tube with bare hands. The oils from your skin will darken the glass and shorten its life. Wipe the glass off with a cloth wettened with alcohol if you did handle the glass.

Thx for that write up. I still can’t get my brain around, even after changing everything with new OEM parts it still doesn’t work. From the switch on the dash all the way back to the bulb.

Is the bulb in fact a high voltage strobe tube? The factory setup is the flasher I posted a picture of and a 12v halogen bayonet mount bulb. If you actually have a strobe tube it must have been changed at some point from the factory system. Is the wiring between Whelen power supply and the strobe flash tube inclusive of all three wires (red, white, black) as described by Gary?

It is. 3 prong plug. Red white and black. Worked fine for years now inop. Hate wiring. It’s just so weird that the bulb will flash when the switch is moved to off. Doesn’t flash when you turn it on. Only off and only once.

Might try and order a new flash bulb from Whelen. Both bulbs do the same thing. One flash when the switch is turned off. Maybe both bulbs are bad.

This looks like a perfect reason to upgrade to a nice, bright LED beacon!

George

Definitely a consideration