Mep 803a no power

[Triton]

Ok, I have no power at the lugs, here's what I have done:
this unit is a tier 2 reset with 600 hrs, has fuse mod and just quit putting out power
Unit running
Am/Vm switched to L3,L1 Single phase
Reconnection switch 120/240 1 phase
flipped ac interrupt switch to closed, green light comes on
Hertz at 60
No fault errors
Convenience plug reads 37 volts
No reading at lugs
Cleaned reconnection switch and AM/VM switch with deoxide cleaner


Hold S-1 to start and voltage comes up to 240 and it produces 120volts at convenience plug and 120volts on L-3 and 120volts on L-1, release S-1 and it goes to zero

One time (in band camp) it did come up with 240 volts on the gauge and at the lugs but hasn't done it since

Is there an easy fix? What do ya'll think I should check first?

 

[Haoleb]

I am a little confused... You said it has 120v on L1 and L3, Are you measuring this between either of those lugs and ground? Do you get 240v between L1 and L3?

I would probably first test the voltage regulator. Outlined on page 97-98 in TM 9-6115-642-24

 

[Hard Head]

Sounds like an issue with the mag pickup. There should be some articles on troubleshooting it.

 

[Triton]

I got 120 volts on L-3 to the neutral and 120 on L-1 to the neutral.

 

[kloppk]

Be sure to check the fuse mod fuse for continuity before doing the voltage regulator checks mentioned above.

 

[Triton]

I went through the TM check for the voltage regulator and everything was good. The fuse on the fuse mod was good. I checked the voltages from the diagnostic port and I found no voltage from the DC exciter field positive or negative. Don't know what that means or if it's related.

 

[Guyfang]

The exciter works if you can hold the S-1 in the start position and the meter comes up to 240 volts. Just for laughs and giggles. Switch to three phase output and see if you have all three legs.

When the set in in the run position, the exciter should not give you a reading. That only happens in the start position.

 

[Triton]

Gutfang you were right about the exciter you have to hold the S-1 switch, the diagnostic diagram doesn't say that but I'll correct my copy. I switched to three phase and there was no voltage on L-1, L-2, or L-3

 

[kloppk]

It's strange you get 37 volts at the convenience outlet but get nothing at he lugs with the contactor close & green light on.
Whatever you get from the outlet should be present across L0 & L3.

Might want to verify that the 37 volts is present across the regulator terminals 3 & 4.

If you went thru the tests in the TM for the regulator and they all passed then according to the TM the regulator is bad.
(Flash working, Quad putting out voltage, voltage pot good)

 

[Triton]

I'll review the TM again, I missed what you said about the regulator being bad.

 

[Guyfang]

You only get voltage at the output terminals, when K-1 closes, and closes properly. And that you have not checked. If the contacts in K-1 were bad, you might not get anything, and you might get something less than what is suposed to be present. I would pull the top off, and check the input side of K-1. The same deal with the 110 volt outlets. If the GFI is not working properly, you might get something, you might get nothing and you might get only a little bit. Everyone thinks that if the GFI is bad, you get nothing. Not always the case. I have seen where the contacts in the GFI were badly eroded. Sometimes it worked, sometimes it didnt.

If you want to know what up with the main gen output, go to the input side of S-8. Ah ha. Yes, S-8. If S-8 is not in order, you are not going to get voltage anyplace else.

You can do both K-1 and S-8 at the same time when you have the top off. Start at the source and that way you got all the bases covered.

 

[Triton]

I re-read the TM for checking the voltage regulator and from what I got out of it is that if the readings are what they say it should read the regulator is bad. So if I got none of those readings on the TM then the regulator is good. Is that correct?

 

[kloppk]

... So if I got none of those readings on the TM then the regulator is good. Is that correct?

Maybe, maybe not
The tests in the TM verify that flash circuit is working, the quad winding is outputting voltage to power the regulator and the voltage pot is in spec.
If one or more of them is not functioning or missing it doesn't imply the regulator is good. It just gives a reason why the regulator wouldn't be operating.

 

[Korgoth1]

The breaker may be bad aswell. You are closing the breaker correct?

 

[Triton]

I'm going to check it again this afternoon and make sure and also test K-1 as Guyfang suggested

 

[Triton]

Here is what I tested this evening
This was with unit running and holding S-1 down after start, there was no difference with AC interrupt closed or open. Without holding S-1 down the readings across terminals tested is 37 to 38 volts.
K-1
120\240 Ph1 A-1 B-1 C-1
120volts 0 120volts
A-2 B-2 C-2
120volts 0 120volts
120\208 Ph3 A-1 B-1 C-1
120volts 120volts 120volts
A-2 B-2 C-2
0 0 0
120\ Ph1 A-1 B-1 C-1
0 0 120volts
A-2 B-2 C-2
0 0 0
S-8
120\240 Ph1 003 001 002
120volts 120volts 0
120 Ph1 003 001 002
120volts 0 0
120\208 Ph3 003 001 002
120volts 120volts 120volts

I hear a relay click when closing the AC Interupt, when I switch S-1 to start I hear a louder relay click. I noticed K-18 clicking and with S-1 down K-18 measured 75 volts. Isn’t K18 a pre-heat relay? There is a device to the left of K-18 but I don't know what that is
I'm learning more every time!

 

[Triton]

Ok that formatting didn't work

 

[kloppk]

Here is what I tested this evening
This was with unit running and holding S-1 down after start, there was no difference with AC interrupt closed or open. Without holding S-1 down the readings across terminals tested is 37 to 38 volts.

Which "terminals"?

K-1
120\240 Ph1 A-1 B-1 C-1
120volts 0 120volts
A-2 B-2 C-2
120volts 0 120volts
120\208 Ph3 A-1 B-1 C-1
120volts 120volts 120volts

These are exactly the voltages expected at these points of K1 assuming they were with respect to L0.

A-2 B-2 C-2
0 0 0

This looks like the contactor K1 was open during these measurements.

I hear a relay click when closing the AC Interupt

That should be K1 closing.

...and with S-1 down K-18 measured 75 volts.

Measured 75 volts where?

Isn’t K18 a pre-heat relay?

Yes

There is a device to the left of K-18 but I don't know what that is.

I believe that would be the cranking relay.

 

[Triton]

I measured the contacts to ground
K-1 had a label on the top of A-1, B-1, C-1 on the left side and A-2 B-2 C2 on the right side

K-18 measured 75 volts on one side of the large wire contact, it was hard to reach and I was trying not to get the crap shocked out of me!

 

[kloppk]

Does your unit have the ground bus bar installed across L0 and GND?
If not then AC voltage measurements must done with respect to L0 unless you are doing a phase to phase voltage AC voltage measurement.

When measuring the terminals of K18 you should only see ~ 24 volts DC or ~0 volts DC depending on what terminals you are checking.
DC measurements should be made with respect to ground (most any metal spot)