Panel lights problem

[murphey]

Interesting (and annoying) electrical problem. Only appears to affect the panel lights (those little GE53 bulbs). Very few of the instruments in the cherokee are self-lit. Most have the GE53 bulb at the corner of the instrument, and the plastic panel overlay has a reflective surface on the back.

On the ground and during runup I can adjust the dimmer and set the brightness exactly where I want it.

During takeoff (full power) the panel lights go to the brightest level. The dimmer pot does nothing other than full bright or off.

In cruise, the lights randomly blink on & off, all at the same time. Which makes sense since all the lights are on the same circuit.

Radios, landing light, position lights didn't seem to be affected. I didn't have the strobe on.

So much for getting night current.

Any ideas?

 

[Clark1961]

Want to borrow my voltmeter that plugs into a cigar lighter socket?

 

[murphey]

Want to borrow my voltmeter that plugs into a cigar lighter socket?

Hm....Might be worthwhile. Going to get back there Friday afternoon. I'm thinking there's a 40+yr old wire that's shorting out or very loose someplace. But completely clueless where it might be.

 

[EppyGA]

The dimmer rheostat controls the base current on a transistor.

 

[jsstevens]

Sounds like the rheostat is getting dirty/tired. They have mechanical sweep arm making contact with a (carbon) disk. If that connection gets loose or dirty you can have theses kind of issues. Sounds like acceleration/vibration causes the issue which would be consistent with dirty/loose contacts in the rheostat.

John

 

[murphey]

argh. When i had the pot replaced 14 yrs ago, I ordered a spare. Who knows where it is now....And in a cherokee, a real pain to get to it. But definitely sounds like the culprit.

There's no local electronics shop around here anymore, so if this is the problem.....rats.

 

[jsstevens]

argh. When i had the pot replaced 14 yrs ago, I ordered a spare. Who knows where it is now....And in a cherokee, a real pain to get to it. But definitely sounds like the culprit.

There's no local electronics shop around here anymore, so if this is the problem.....rats.

If you can get to it a squirt of contact cleaner (try CRC 2-32) might just fix it. Squirt it inside and turn the knob all the way back and forth a few times. CRC leaves no residue but will wash out the junk.

John

 

[Stewartb]

http://www.maxpulsemaxdim.com/maxdimproduct.htm

 

[murphey]

http://www.maxpulsemaxdim.com/maxdimproduct.htm

$225. Amazing what an STC will cost. Without the STC, it's about $10. I think it's a Clarostat, rebranded by Piper.

Contact cleaner first. This is not what I wanted for a Christmas present.

 

[weirdjim]

The dimmer rheostat controls the base current on a transistor.

Not in a 40 year old aircraft it doesn't. Semiconductor dimmers didn't come along that long ago in most GA aircraft.

Jim

 

[weirdjim]

If you can get to it a squirt of contact cleaner (try CRC 2-32) might just fix it. Squirt it inside and turn the knob all the way back and forth a few times. CRC leaves no residue but will wash out the junk.

Rat Shack still sells it.

Jim

 

[jsstevens]

Rat Shack still sells it.

Jim

Glad to know that. I used to keep "Tuner Shower" around for general electronic contact cleaning and I haven't been able to find that for years. Magical stuff, that was.

John

 

[weirdjim]

$225. Amazing what an STC will cost. Without the STC, it's about $10. I think it's a Clarostat, rebranded by Piper.

http://www.mouser.com/Passive-Compo...s-Rheostats/Rheostats/_/N-9q0yj/?Ns=Pricing|0


Jim

 

[Stewartb]

I won't jeopardize my mechanic's livelihood in order to save a couple hundred bucks. I saw a mechanic friend have his cert suspended for a less egregious return to service sign-off. Not worth it to me.

FWIW I got rid of my factory panel lights and rheostats long ago. I added a glow strip under the glare shield and run it through a MaxDim. I'll never go back.

 

[brenec]

My Piper Dakota suddenly developed a problem with its panel lights and running lights. When I switch on the dimmer, the running lights would normally come on, but today they did not. When I advanced the dimmer to full bright, the circuit breaker popped. Something is amiss that wasn't wrong the last time I flew...

 

[murphey]

Update almost 6 yrs later.....I installed the MaxDim back then. Waiting to do the other one next time the cherokee’s in the shop for electrical stuff.

 

[Daleandee]

There's more than one way to fix a distressing situation ...

 

[MajorTurbulence]

Update almost 6 yrs later.....I installed the MaxDim back then. Waiting to do the other one next time the cherokee’s in the shop for electrical stuff.

My panel lights in my Archer 2 often don’t come on when I turn the thumb wheel immediately, but the nav lights are on immediately, as well as my newly installed TailBeacon. However, these lights suddenly go on to the dimmed setting sometime after startup while taxing after a little vibration. Since it almost always behaves this way, it is way down on the totem pole to address, but it is good to know the Maxdim will work if I need the rheostat replaced.

 

[455 Bravo Uniform]

@murphey @Stewartb or anyone else, can you guys show the installed strip, MaxDim, and how it’s powered - battery, or ship? Logbook entry needed? Simple Walmart trip, Amazon?

Edit - sorry, just saw this was a necro...

 

[Dan Thomas]

Not in a 40 year old aircraft it doesn't. Semiconductor dimmers didn't come along that long ago in most GA aircraft.

Jim

Our 1970s 172s had them. Two power transistors on a heat sink. A dual concentric-shaft pot. There is a small resistor between the low end of the pot and ground to keep the transistor base bias current up a little so that you don't end up with light in only the last half of the pot's range, since an incandescent bulb won't make light at 2 or 3 volts. That resistor fails or comes loose and the pot, a voltage divider, loses its ground reference and the base sees pretty much full voltage and the lights go bright. Flickering on and off can be caused by a loose resistor connection.

Edit: Sorry. I just saw the date. Old post. But the troubleshooting info still applies.

 

[murphey]

@murphey @Stewartb or anyone else, can you guys show the installed strip, MaxDim, and how it’s powered - battery, or ship? Logbook entry needed? Simple Walmart trip, Amazon?

Edit - sorry, just saw this was a necro...

Maxdim installed by the A&P, simple logbook entry because they’re STC’d. Check the website.

 

[Arrow76R]

I agree with "weirdjim"...my '69 Piper Arrow uses transistors to dim the panel and overhead lights.

 

[Stewartb]

QUOTE="455 Bravo Uniform, post: 2921157, member: 26226"]@murphey @Stewartb or anyone else, can you guys show the installed strip, MaxDim, and how it’s powered - battery, or ship? Logbook entry needed? Simple Walmart trip, Amazon?

Edit - sorry, just saw this was a necro...[/QUOTE]

Glow strips- Aircraft Spruce. MaxDim- Local instrument shop.

[

 

[brenec]

Not Necro anymore! I realized that on my Dakota, one rheostat controls the radio lights and Nav lights, one of them controls the instrument lights. Only the instrument light system appears to be acting strange. I'm going to test it again, but I think the Nav lights may still work.