Panel 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

"Steve - KDMW" wrote in message
...
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.

Steve - KDMW wrote:
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

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.

--

Tauno Voipio
PA28RT-201T
EFHF

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

"Steve - KDMW" wrote in message
...
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

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


wrote in message
...

.. 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



"RST Engineering - JIm" wrote in message
m...
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


wrote in message
...

. Wirewound pots
aren't common in the resistances used here and they cost too much.

Dan

RST Engineering - JIm wrote:
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



"RST Engineering - JIm" wrote in message
m...
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


wrote in message
...

. Wirewound pots
aren't common in the resistances used here and they cost too much.

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.

--

Regards, Ross
C-172F 180HP
Sold
KSWI

RST Engineering - JIm wrote:
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


wrote in message
...

. Wirewound pots
aren't common in the resistances used here and they cost too much.

Dan




That is exactly where my pot would burn out.

--

Regards, Ross
C-172F 180HP
Sold
KSWI