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Test yee circuitry skills!

s_tones

Well Known Member
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This is a dimmer circuit in my plane. Combo on-off switch/potentiometer controlling panel lighting circuit via a transistor. Makes sense except for the switched circuit (via 3-4) in yellow.
I can't figure out why it's there. The (3-4) switch appears to connect "1" to ground in conjunction with movement of the pot. I cannot see what use this has.

Any thoughts?

Thanks,
Steve
 
Without knowing what is connected to connector pin 1 it's impossible to know its purpose. It appears to be a normally closed switch providing connection to gnd with the pot in the off position. Once the pot is turned on the closure to gnd opens but it's not connected anywhere in this schematic.
 
Thanks. Yep, that's what I thought. Oddly I can find zero info on what might be connected to "1". But it appears that it has no bearing on the function of the panel light circuit. I will have to look again for some reference to that unlabelled pin.

Steve
 
If I had to guess, this is a piper arrow dimmer circuit. The connection to ground pulls the landing gear lights to ground, applying full power and thus full brightness to the lights. When the dimmer is turned on, the aforementioned lights brightness level is controlled thought the bipolar dimmer. The other pot serves to control the avionics dimmer circuit, and also turns on the nav lights by connecting 1&2.
Just a guess.....
 
Circuit quiz

Looks exactly like the dimmer circuit in my old Arrow. Had to replace those NPN transistor several times along with a string of grounding issues. When the pot is at minimium R you get full bright on the lights and when the pot is adjusted you modify the bias on the base of Q1 or Q2 dimming the lights.
 
Last edited:
yup

Very good! Actually piper archer II.
There is no landing gear though so maybe that switch is just hanging out, unused? Odd that it's wired up at all though. Maybe they just setup the same switch and wiring and then use it on several planes in the series.

In my case it appears the transistor is OK (replaced) and the pot is shot.

Steve
 
They all use the same dimmer setup. If your pot is shot you will have a tough time finding one with the proper switch. That relay is also used to dim the annuciator, that's why it's used in the Archer also
 
yup, yup

Thanks to you all. A veritable fount of knowledge here as always.
Annunciator! Yep, I think that's it.

You are right. It's a bear to find these parts.
As it happens, after a serious hunt I found a guy selling 3 new ones included along with a bag of other less useful junk. Bought the lot.

Steve
 
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