No field current to alternator

[231MJ]

I have a 262 with dual alternators.  Last week the belt driven alternator stopped charging.  I assumed I was in for a replacement (it's been on there for a long time).  After I took the alternator off I check if there was current to the Field - but no current.   I believe the Regulator controls current to the field so does this mean the Regulator has gone bad?  I need this fixed for Oshkosh...

Thanks, all.

[MikeOH]

I'm not following what you are saying.  How did you measure field current if the alternator was removed?!?

[DCarlton]

I’m no expert but isn’t there a field switch, possibly a fuse and a breaker that could cause problems too along with the regulator?  

[Pinecone]

You measure VOLTAGE at the field input to the alternator.  Not current.

There is a switch, some connections, wire, and the voltage regulator.  You need to check voltage at each connection, starting with the VR.

[231MJ]

Thanks for the quick response. I used incorrect terminology, yes, measure voltage.  Yes, there is a switch, a 5 amp breaker and the VR.  There is voltage at the switch and the breaker and I assume at the VR since the gear driven alternator is charging, but I'll check for voltage at the VR also.  I traced the field wire for possible breaks and didn't find any.  Same question, assuming there is voltage at the switch, the breaker and at the VR, if there is no voltage at the field wire at the alternator, is this a VR issue?  Anyone have experience with this?

[skykrawler]

Check your maintenance manual.

You probably have two regulators with a paralleling connection.

To eliminate the possibility the wire is bad check the field wire at the regulator.

The regulator may shut down for overvoltage.  You have no annunciator indications?

[Pinecone]

6 hours ago, 231MJ said:

and I assume at the VR since the gear driven alternator is charging, but I'll check for voltage at the VR also

Do you only have one VR?

My 252 has dual alternators.  I have two VRs.

[N201MKTurbo]

Voltage regulators have power inputs and power outputs. The first thing to do is make sure you have power getting to the VR. Next se3 if you have power  coming out of the VR. 
 

With the engine off and the master and field on, you should get near battery voltage at the regulator output. You could use Doc’s trick and check if you have field current by sticking a paper clip on the rear bearing. If it sticks, you have field current.

[231MJ]

Up date:

VR is getting power and there is continuity to the field wire at the alternator so no broken wire (but no voltage from the field wire at the alternator).  There are two VRs as suggested by Pinecone and Skykrawler, the VR for the second alternator is made by Precise Flight (or at least sold by Precise Flight) - see attached picture.  Called Precise Flight and got VM and so far, no return call.  Called Lamar Technologies and got a very helpful tech that said a VR415F is a suitable replacement for the Precise Flight DGR1.  The existing VR is 35 years old so I'm taking a gamble that it needs to be replaced.  Spruce had one and it should be here on Friday.       Precise Flight VR for 262.pdf

More to follow.  Thanks for the ideas, everyone.