MEP802A AC Voltmeter shows voltage when left in start position

[genmech]

I have this issue with the AC voltmeter not showing voltage. I looked up AC VOLTMETER (VOLTS AC) DOES NOT INDICATE VOLTAGE in the TM, followed the steps, still having the issue.

• Replaced the gauge, no change.
• Tested AM/VM switch, no breaks
• Tested potentiometer, showing ohms as I move it. Can't remember if it was in the 4500 to 5500 ohms range
• Replaced the AC regulator.

Here is the kicker with changing out the AC regulator. The meter shows 220 when holding the master switch in the start position. Once I let go, it goes back to 0.

• Tested voltage reconnection switch, no breaks.

The gen outputs power, showing 24V.

Any ideas?

 

[jamawieb]

Are you getting voltage at the outlet or lugs??? If not, look in the TM under troubleshooting No Voltage. Sounds like the exciter is working but a diode may be bad in the head.

 

[genmech]

I was receiving 24V on the output terminals. I replaced a diode on CR2 with a brand new one

 

[jamawieb]

Did you test K15 exciter relay? Also make sure you use -24 manual, it will be more effective than the others.

2-33-2.
Testing.
a.
b.
c.
d.
e.
f.
g.
h.
Shut down generator set.
Release control panel by turning two fasteners and lower control panel slowly.
Remove applicable relay, paragraph 2-33-3.
Set multimeter for ohms and check for open circuits between terminals 7 and 4, 8 and 5, and 9 and 6. Check
for closed circuits between terminals 7 and 1, 8 and 2, and 9 and 3.
Connect 24 VDC source to terminals A and B, and listen for audible actuation of relay. Set multimeter for ohms
and check for open circuits between terminals 7 and 1, 8 and 2, and 9 and 3. Check for closed circuits between
terminals 7 and 4, 8 and 5, and 9 and 6.
If indications are other than above, relay is defective and must be replaced.
Install relay, paragraph 2-33-4.
Raise and secure control panel.

 

[genmech]

I removed the k15 and checked the terminals based on the diagram on the component itself. I think I've even tried a good K15 from another gen. Do you have any other ideas? I will try the other K15 tomorrow. I think I should check the cabling on the socket itself while I am there as well.

 

[Guyfang]

OK, Stop. Give us more info to work with.

1. Is this set new to you?
2. Have you ever seen it work right?.
3. If it worked right before, did you or someone else fix, repair, change or adjust anything?
4. Why did you change the meter?
5. How did you check the AM/VM switch? Powered up? or with no power.

 

[genmech]

This gen is new to me.

It has never worked right. I was told to fix it, so I am attempting to do so.

Changed the meter in hopes it was something simple.

I followed the tm for the am/vm. Tested each position based on the wiring diagram. I removed it and tested for any breaks.

 

[Guyfang]

2-52-2. Testing.a. Shut down generator set.b. Remove AM–VM transfer switch, paragraph 2-52-3.c. Set multimeter for ohms and check switch for continuity. Refer to Electrical Schematic FO-1 (S-6 CircuitSchedule) to determine circuits made to corresponding switch position.d. Check continuity in all six switch positions.e. If open circuit is noted in any switch position, AM–VM transfer switch is unserviceable and must be replaced.f. Install AM–VM transfer switch, paragraph 2-52-4.

I assume you used this procedure to check the S-6, AM/VM switch.

The M-1, AC voltmeter gets its signal from the S-6, AM/VM, pins 32 and 15. If the meter shows voltage while the S-1 start switch is in the start position, then the meter is good. And since the meter works, the S-6 is probably good also. Have you double checked the wires hooked to S-6? Not just tagged them when you unhooked them and rehooked them by your tags, But looked at wire numbers, and pin numbers? Have you checked to see that the S-8 is turned to the correct position? If you have it in wrong position, then you could be reading correctly, 220 volts. Turn it to the 120/208 position.

The problem sounds like you get the gen set started, it lights off the main AC, and then when you let go of the S-1, the power drops off. The very first place I would look, is the S-1 switch, to see if its wired correctly, and then I would test S-1. Take a picture of S-1, from a couple of angles, and post them. The we can see if it an old style S-1, and if the Diode is on it.