Electrical Problems

[Hyflyer86]

Hi Guys:

I recently had a local shop change the front alternator on my '73 P337 due to a fault light. When they did the test run, still had the light; the gear doors opened; the OAT/Tach CB popped; the warning horn was sounding. I took it back to the garage. I am an A&P but never worked on a 337. I just bought it a month ago.

First the gear doors; scary. I couldn't find a faulty wire or circuit in the front engine compartment or NLG well. I went to the wiring diagram and looked for logic that would allow the power pack to start and the door to open. I disconnected the #4 terminal block wires in the NLG well. That did it. I suspected a shorted diode in the circuit but I could not find the diode. Anybody??

I pulled the dual warning and over voltage sense boxes. Warning box looks good. Over voltage box had shorted diode and burned trace. I replaced/fixed those. I re-installed both but did not power system up yet. I suspect that will fix the alternator light. The warning horn is real and I suspect that a gear switch is tripped.

Back to the electrical schematics to look for the popped CB on the OAT/Tach lines. I know the mechanic removed the mags to get the alternator out. I think that he may have connected the mag tach wire to the alternator instead of the tach points? I have not been able to ascertain that connection at this time. I am open to suggestions where to look for that gremlin.

Bill N86C
Hyflyer86

[Skymaster337B]

Try a new battery. Even if voltage is good it could have weak cells.

[hharney]

sounds like you need a different mechanic

[Hyflyer86]

Yes, I do! This is the first time that I have farmed out any maintenance on any airplane, for this very reason. What is particularly bad is that I don't know what he really did so that I could easily make the corrections. On the other hand, it will give me the opportunity to learn the aircraft very quickly. I would like to fly it though, now and then!

Hyflyer86

[Gord Tessier]

They are an easy fix. There is a micro switch on top of the throttle linkage on both engines. It's attached to a silver roundish cam. Simply undo the little screws and move the switch so it hits the flat spot on the cam at the desired place. Then tighten it down.

[Hyflyer86]

Thanks Gord:

Switches are ok. The warning box is messed up. I am working on it now. Thanks for responding. I appreciate it.

Hyflyer86
Bill

[Hyflyer86]

Hi Guys:

Well, I have solved my alternator problems. After changing the front alternator, I still had warning lights. I pulled the warning/control box and replaced a diode. I calibrated the control voltage for front and rear alts. I replaced a bad wire on the firewall unit. All good.

After the mechanic changed the alt for me and powered up the system, the gear doors opened, and the warning horn sounds when you turn on the master. I have changed a couple of components in the warning box and the throttle switch on the front engine which was failed. Still horned.

I have jacked the plane, checked all up/down switches, squat switch, landing gear selector switch, and the up and down lock circuits. They are all good. Cannot get the doors closed. Could swing gear by putting power on the solenoid and operating the master but the gear would not lock up or down due to tripping breaker.(p-switch not in circuit with hot wire). I could lock the gear down with the hand pump.

Now, off the jacks. Not getting power to the solenoid through the pressure switch. Tracing the wire from the gear ind cb and lose it in the large bundle behind the panel. No continuity from cb to solenoid, p-sw at powerpack plug or ind lites, including Press to test. My LAN Cable tracer doesn't seem to work either. It loses power just after the connection at the cb. I think I am at wits end due to brain size.

Can anyone offer trouble shooting help? How about the contact info for an expert to come and solve it? Southern Oklahoma.

Bill Hyflyer86

[Red Air Rambo]

Hi Bill,
My 73 P model was having some electrical issues and it turned out to be a bad contactor. We ended up replacing all three due to age. I would check the voltage coming through the battery cable to the contactor too.

Brent

[Hyflyer86]

Thanks for the reply Brent. I do have power at the LG contactor but no power to activate it when commanded. I will check all of the contactors on my 73 -P too. Thanks again.

Bill Hyflyer86

[Red Air Rambo]

Just to clarify I was talking about the three main contactors located on the firewall beneath the pilots side cowl. There is a battery, front, and rear. In my case the battery contactor went south causing all kinds of strangeness.

[Hyflyer86]

Hi Brent:

Yes, you were clear. My three contractors are good. The contactoe that runs the pump motor in my power pack has 24v to it but no juice to operate it coming from the gear indicator CB. This happened after a front alternator change. When we turned on the master the doors opened and warning horn sounded. Cannot get the doors closed or the horn silenced via normal operation. Next step is to call in an air strike. LOL! Thanks for the response.

Bill

[Red Air Rambo]

Another problem I ran into was a solenoid burnt out on the gear powerpack not allowing operation of the gear, I believe there is a SB on this and the actuators. I had Rick Cox of Coxairparts out of Whichita overhaul them.

Best of Luck,
Brent

[Hyflyer86]

Yes, good advice. I have talked to Rick since I was originally suspicious of the power pack. At the moment, having looked at the solenoids electrically, I think that they are ok. I am trying to figure out why I have no power to the solenoid when I select up or down, and why I can't get the doors closed. The door problem could be in the Power Pack priority valve.

When I look at the schematic for the gear operating system, it would appear that I am not getting the circuit through the up/down lock switches to the gear lever/switch. I have looked at each switch with a meter and all are working. I have looked at the continuity of the circuits and they are good. The squat switch is good. That all brings me back to a bad wire/connection somewhere between the NG well and the PP; or the CB and the PP.

I have a new cable tracer that seems to work now. I am going to try tracing the wires from the CB and from the PP. So far, it doesn't appear that the schematic is the same as the airplane. It is a 42 year old plane, so a lot can happen in that time. It seems to not add up at this point. I suspect that I am missing some key element in the troubleshooting loop. Luckily, I am more persistent than smart.

Thanks so much for the conversation, it really helps me get focused.

Bill Hyflyer86

[Hyflyer86]

Red Air Rambo:

If you look at the electrical schematic for the landing gear control system, would you know the physical location of the diode shown in wire S-GD12 leading from the LG switch to the LG solenoid in the schematic? It may be blown but I can't find it.

Thanks,

Bill Hyflyer86

[Red Air Rambo]

I don't know its location but Don Nieser should. Commodore aircraft 405-722-4079.