Final runup for airworthiness sign off after 15 months in the shop, 50a blows

[SilentT]

So I’m headed to Idaho to get my bird 84J after almost 1.5 years in the shop.

ap is happy, I’m happy, he does final runup today while I’m in route and 50a cb blows for lower switches. He said cross tube felt warmer like they shorted to it, look as though they had fallen on it. But when he pushed them up off of the cross bar the cb would not reset.

I'm headed there tomorrow and while not an ap I hope my EE degree can be of help to him. I’ve already flown the transition pilot across the country lol.

any thoughts or recommendations here beyond look for burns?, I’m guessing checking continuity to ground, then start removing loads / all loads until it has no ground link and will hold a reset?

Edited October 20 by SilentT

[clh]

Your last statement is the  best approach.  Throw all downstream breakers and turn them on one by one until it trips.

I know of a Mooney that was converted from a generator to an alternator, but the breaker and wire was not changed. If the battery is quite discharged, the 50 amp alternator will over power the 40 a breaker.  This was an older mooney.  It was solved by upgrading the wires and breaker.  It is possible that the alternator is just surging when you start up.  The breakers also "age"  the more they trip the weaker they get.

[mike_elliott]

Good luck Dan, should be fairly easy to isolate. Have the mx retrace his work and see if any of it could have caused a short also, which I’m sure he is already doing

[Aerodon]

10 hours ago, SilentT said:

So I’m headed to Idaho to get my bird 84J after almost 1.5 years in the shop.

ap is happy, I’m happy, he does final runup today while I’m in route and 50a cb blows for lower switches. He said cross tube felt warmer like they shorted to it, look as though they had fallen on it. But when he pushed them up off of the cross bar the cb would not reset.

I'm headed there tomorrow and while not an ap I hope my EE degree can be of help to him. I’ve already flown the transition pilot across the country lol.

any thoughts or recommendations here beyond look for burns?, I’m guessing checking continuity to ground, then start removing loads / all loads until it has no ground link and will hold a reset?

The wiring goes from the 50A CB to one side of the switch busbar, then that is jumpered over to the master switch side.  If it is tripping with all switches in the off position, then this wire or the busbar itself is shorted to the frame.

Or after tripping once, the CB is broken.

Aerodon

 

[1980Mooney]

Your 84 M20J is a 14 volt system. And you say it has been in the shop idle for 1.5 years.
 

Did this happen while cranking or immediately after engine started or after bring RPM up?  Was the ammeter pegged to full draw the whole time? Was this before he turned the avionics master switch on or after? 

I always look for the obvious problem first. Was the battery fully charged? You need to observe the voltage and current draw at same time. Low voltage draws more amps. Your battery is in back and most current draw is in front. The power has to flow through relays in back which may not have been exercised in a long time. If voltage is low and amps high then the relays and any connections that have been disturbed during the long repair might be causing voltage drop. 

Edited October 20 by 1980Mooney

[SilentT]

Oddly enough every single rubber mount for the pannel broke, and the damn thing fell on teh cross bar and shorted out radio master screw. 

A&P got new spacers fixed er right up. 

now in 2nd shop, asked em to check it make sure its ok.

[PT20J]

It’s common for those LORD panel shock mounts to break. They are only there to reduce vibration on panel-mounted gyros. If you go glass, it’s best to replace them with solid spacers. There have been some reports of issues with Garmin ADAHRS if the panel is shock mounted. 

[Flyler]

1 hour ago, SilentT said:

Oddly enough every single rubber mount for the pannel broke, and the damn thing fell on teh cross bar and shorted out radio master screw. 

A&P got new spacers fixed er right up. 

now in 2nd shop, asked em to check it make sure its ok.

I was just about to mention to look for this issue.  I have a pile of replacements sitting on my desk, waiting to be installed.  Mine are all broken as well.

[Aerodon]

The panel should have these plastic coated standoffs to prevent it dropping too low.  I use aluminum spacers to replace the rubber lord mounts, but the OEM panel holes will not match the rivnuts in the airframe.  They needed the rubber mounts to allow some degree of misalignment.

 

Aerodon