Post lights

[flyboy0681]

The post light fuse keeps blowing at $10 a pop. Before an expert is brought in to investigate, is there anything obvious that I should look at?

Nothing on the panel has changed recently which would have caused this.

[Skywarrior]

Just a SWAG...

Is there any trapped moisture around the bulb or its socket?

[fantom]

Swag #2......are you absolutely certain your installing the correct size fuse?

[flyboy0681]

No moisture, the plane is hangared and hasn't flown in precip in recent history.

I compared the original one with the new one (as I scratched my head wondering why it cost $10) and they had the same specs.

The fuse didn't immediately blow, it took about 10 minutes of use.

[Steve65E-NC]

On my 65E, the compass light is on this same circuit. It seems easier to short than post lights. Include it in trouble shooting.

[larryb]

There are 2 basic possibilities:

1) Fuse is too small. Measure the current with an ammeter, compare to fuse rating and wiring diagram. Compare to what is reasonable. Without measuring mine, I would think the lights should draw no more than 1 or 2 amps tops.

2) An intermittant short. That's harder to find, and involves visually inspecting all of the wiring in the circuit. My shop found a short in my compass light wire where it had been squashed in the mounting of the compass to the tube frame.

Larry

[jwilkins]

Do you have two separate dimmers, one for the post lights and one for the glare shield lights?

I'm assuming you do and since you specified the post lights are blowing the fuse that the glare shield lights do NOT blow the fuse when the post light dimmer is off.

The easy things to check first are frayed insulation on the wire going to the compass and the wire going to the glare shield.

There are a couple of trouble shooting things you can do on the ground; you can solder wires and pins to a circuit breaker (same or lower rating than the fuse) OR a lamp while you are wiggling wires and lamp bases around. A dead short will make the lamp that replaced the fuse light up, or, if you put in the breaker, the breaker will pop and it won't cost $10 to reset it.

Once every thousand years or so you will find a bulb that shorts internally when the filament blows. If you can't find anything else you can check each bulb in the post lights that you can R&R. in most airplanes the post light circuit is also connected to some internally lighted instruments which is an additional complication.

Trouble shooting with those blasted fuses at $10 a pop is expensive. Try the circuit breaker for trouble shooting. There is no real magic to this; it's just systematic step by step trouble shooting. Even if you give up and take it to the shop you will be able to tell them what you already checked.

[flyboy0681]

Good suggestions Jim. The placing of a circuit breaker in the line will help with the process since we'll be able to hear it click when we are getting close.

[N601RX]

I believe your plane wil have the new transistor dimmer circuit instead of the older style wire wound pots. Several people have had trouble with the transistors leaking and finally completely shorting.

[DonMuncy]

When did the change to the transistor dimmer occur. I have just started having the fuse blow on the panel lights, but have not had time to work on the problem yet.