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Aviation Forum / General / Aviation / July 2009Panel lights breaker pops
Has anyone seen this?...1974 Warrior panel lights don't come on, and when I turn the rheostat past a certain point (almost full bright) the panel lights breaker pops. I'm thinking it's the power transistor, at least that's what I'm going to try first (along with cleaning the rheostat) since it's the cheapest thing to do. Steve PA28-151 KDMW > Has anyone seen this?...1974 Warrior panel lights don't come on, and > when I turn the rheostat past a certain point (almost full bright) the > panel lights breaker pops. I'm thinking it's the power transistor, at > least that's what I'm going to try first (along with cleaning the > rheostat) since it's the cheapest thing to do. Before you start blindly changing parts, troubleshoot your problem by measuring the current through that circuit with an ammeter. If you have too much current for that circuit, then figure out why. If the breaker is popping too soon, then replace the breaker. Another possible cause is a bad connection near the breaker heating up, conducting heat into the breaker, and causing it to trip. Vaughn I did have a bad transistor that controls various lights in the cherokee. I think I paid $4.00 for the transistor, and $65 in labor. But, I also bought a complete set of 4 extra transistors because I know they'll die - afterall, they were original 1969 equipment. I'm astonished they lasted this long. > Has anyone seen this?...1974 Warrior panel lights don't come on, and > when I turn the rheostat past a certain point (almost full bright) the [quoted text clipped - 5 lines] > PA28-151 > KDMW My bets on a genuine short circuit in the lights, maybe a bad bulb. There is not enough current to pop the breaker before the setting is nearly full.  SignatureTauno Voipio PA28RT-201T EFHF I would bet on a short to ground on the lights too. If you keep turning the dimmer pot up to pop the breaker, you will eventually cause the dimmer pot to fail which will be more expensive than you would guess!! These cirucits are notoriously poorly protected for over current conditons. Bill Hale BPPP instructor On Jul 8, 6:43 pm, Blanche <bco...@blackhole.nyx.net> wrote: > I did have a bad transistor that controls various lights in the > cherokee. I think I paid $4.00 for the transistor, and $65 in labor. > But, I also bought a complete set of 4 extra transistors because > I know they'll die - afterall, they were original 1969 equipment. > I'm astonished they lasted this long. Common problem on older Cherokee models. Chaffed wiring where it passes thru bulkheads in wings or fuselage. Isolate one circuit at a time to pinpoint correct wiring path to look at. Larry > Has anyone seen this?...1974 Warrior panel lights don't come on, and > when I turn the rheostat past a certain point (almost full bright) the [quoted text clipped - 5 lines] > PA28-151 > KDMW On Jul 24, 5:50 pm, "Larry D. Cosby" <lcosby at knology dot net> wrote: > Common problem on older Cherokee models. Chaffed wiring where it passes thru > bulkheads in wings or fuselage. Isolate one circuit at a time to pinpoint > correct wiring path to look at. It wasn't the nav lights that were popping the breaker; it was the panel lights. If there's a short there, they shouldn't come on at all. The easiest path would be to ground, not through the bulbs. My bet is a bad breaker, or a corroded or burnt crimp terminal at the breaker. The breaker's internal contacts oxidize with age and start making resistance and heat that fools the bimetal thermal strip into popping. The rheostat (potentiometer) carries only the tiny base current for the transistor; flickering lights should be the result of a worn pot, not a popped breaker. Unless, of course, it's a wirewound pot and the wires are frayed and broken inside. Not likely, though. Wirewound pots aren't common in the resistances used here and they cost too much. Dan That's unfortunately not the case, Dan. Everything Wichita turned out up until the mid 60s used Ohmite wirewounds. Of course, they would burn out right where the wire got the hottest ... where the resistance of the bulbs and the resistance of the pot were the same. THis was almost always 10% or so from the high side contact of the pot. Jim . Wirewound pots > aren't common in the resistances used here and they cost too much. > > Dan Just looked up ... the suckers are running $25-30 at the wholesale electronics suppliers. I don't want to know what they cost when they come in a Beech box. Jim > That's unfortunately not the case, Dan. Everything Wichita turned out up > until the mid 60s used Ohmite wirewounds. Of course, they would burn out [quoted text clipped - 8 lines] >> >> Dan > Just looked up ... the suckers are running $25-30 at the wholesale > electronics suppliers. I don't want to know what they cost when they come [quoted text clipped - 14 lines] >>> >>> Dan I bought correct ones from aircraft salvage yards for $50 -$70 each. I sure would have like to know the part number for a replacement. SignatureRegards, Ross C-172F 180HP Sold :( KSWI If anybody has an old one laying around, burned out or not, and you can tell me the airframe it came out of and send it to me, I'll cross it to the correct Ohmite part with a Mouser part number. Ji9m >> Just looked up ... the suckers are running $25-30 at the wholesale >> electronics suppliers. I don't want to know what they cost when they [quoted text clipped - 4 lines] > I bought correct ones from aircraft salvage yards for $50 -$70 each. I > sure would have like to know the part number for a replacement. > That's unfortunately not the case, Dan. Everything Wichita turned out up > until the mid 60s used Ohmite wirewounds. Of course, they would burn out [quoted text clipped - 8 lines] >> >> Dan That is exactly where my pot would burn out. SignatureRegards, Ross C-172F 180HP Sold :( KSWI > On Jul 24, 5:50 pm, "Larry D. Cosby" <lcosby at knology dot net> > wrote: [quoted text clipped - 15 lines] > > Dan My Cessna use a wire wound pot that kept burning out. I took one apart and was it cheaply made. SignatureRegards, Ross C-172F 180HP Sold :( KSWI Never ever forget that every part on the airplane was supplied by the lowest bidder. (paraphrase from John Glenn) Jim > My Cessna use a wire wound pot that kept burning out. I took one apart and > was it cheaply made. |
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