I've found many approaches out there as to how to do troubleshooting.  The initial approach is usually, very little diagnostics and just replace the usual suspects.  Sounds like your problem does not lend itself to the usual approach. That's why your asking.  Leave it to me to restate the obvious!  Here's some questions that need aswering. Others may have more, this is just to get you started.

When you lost electrical, did the alternator output or field breaker breaker trip?

What did you have operating (switched on) at the time of the failures?

What were the weather conditions?

Have you reviewed the sequence that you use before turning the master on verus the sequence the your mechanic uses?  If you go by a check list before turning the master on and he doesn't, that might be a clue.

Do you have an external power plug for your battery?  there is a circuitry associated with them that bypasses most of the electrical in the plane.  Is there an intermmitent failure mode in it that could cause this?

You obviously have been sitting in the airplane when you get this failure, is the mechanic sitting in it or was he standing next to it?  I was thinking of some kind of stress related failure with some connection?

Well this is just food for thought.. let us know what you find out.

Ans to some of Barry's questions:

When you lost electrical, did the alternator output or field breaker breaker trip?

No.


Q  What did you have operating (switched on) at the time of the failures?

A  First time, in flight everything except lights.  Afterward failure occurs at the start of pre-flight while standing outside the plane with nothing on.


Q  What were the weather conditions?

A  1st time -5C -SN in flight, after that it hass occured in the morning when it is about 5C in the hanger.

Q  Have you reviewed the sequence that you use before turning the master on verus the sequence the your mechanic uses? If you go by a check list before turning the master on and he doesn't, that might be a clue.



Q  Do you have an external power plug for your battery? there is a circuitry associated with them that bypasses most of the electrical in the plane. Is there an intermmitent failure mode in it that could cause this?

A  No.

Q  You obviously have been sitting in the airplane when you get this failure, is the mechanic sitting in it or was he standing next to it? I was thinking of some kind of stress related failure with some connection?

A  Both. See above.

Well this is just food for thought.. let us know what you find out.

A thanks, I appreciate the help.

After flying last night and having it work OK I went back this AM to check and found the master does  not work again.  Wonder if it is broken wire or poor connection that contracts in cold and loses continuity...  (maybe like message from Rich...)

Tom, you might try this. Turn the master switch on and gently flex the wires terminated at the switch and also the relay.

Had yopu checked the connections and terminals at the battery to be clean and tight along with them not broken at the battery itself. Also check to see that the connections at the solenoid are also clean and tight. Also make sure that the battery is in a good charged condition. You may want to try another battery as a jumper when it fails to work.

Good Luck
Bill

Having mechanic replace the diode.  this is part of 1993 AD that has now (it seems) caused further problems!!   Took diode out of circuit until part arrives  -no problems thus far.

Also tried the advice in other notes (connections, battery, etc) Thanks for the help!!!

I'll follow-up once we know for certain.  It seems like the failure would occur more in the AM when it was cool.  Will test old diode after cooling.


tom.