MEP 804B under voltage/regulator issues

[grooving-gru]

Hello everyone,

im pretty new here but have adsorbed and found a tremendous amount of information here to troubleshoot my 804B. Just a quick background on the set.
2010 MEP 804b with 185 hours on it, bought it at auction. Engine wouldn't start when i first started working on it and discovered a missing MPU. After installing a replacement and adjusting it, the engine fire right up. The under voltage light comes on as soon as i let go of S1. I proceed with the troubleshooting section in the TM with section 4-2.1 for internal crack relay test. This passed. Then moved on to section 4-1.2 for the voltage regulator and it failed. ( I have the fuse mod) Here's what i've got

4-1.2 Testing (AC Voltage Regulator, P/N 01-21501-2, for MEP-804A/MEP-804B).

h. Set multimeter for DC volts and connect positive lead to wire 141A. Connect negative lead of
multimeter to terminal 3 of AC voltage regulator. Start generator set and operate at rated
frequency. Move and hold MASTER SWITCH in START position. Multimeter should indicate
between 4 and 12 VDC.

I have anywhere between 18-22VDC here

j. Set multimeter for AC volts and connect to terminals 10 and 11 of AC voltage regulator. Start
generator set and operate at rated frequency. Move and hold MASTER SWITCH in START
position. Multimeter should indicate 110 to 160 VAC.

Im only getting 7 VAC


l. Disconnect wire 137A from terminal 5 of AC voltage regulator. Set multimeter for ohms and
connect positive lead to wire 137A and negative lead to terminal 4 of AC voltage regulator. Move
VOLTAGE adjust potentiometer to full CCW position. Multimeter should indicate no more than 2
ohms with FREQUENCY SELECT switch in 60 Hz position or 50 Hz position. Move VOLTAGE
adjust potentiometer slowly CW while observing multimeter. Multimeter should increase smoothly
to approximately 20,000 ohms

Im getting an open circuit here

i would assume that the voltage regulator is fried and i will take a look at that later, what i have an issue with is that im getting 18-22 VDC on terminal 1 and 3 when it should be 4-12. After doing some more research in the forum, this appears to be the flashing circuit? I went on and performed the following test posted by guyfang in another thread

All this is with S1 held in start position
1. measure dc voltage at S1 terminal 7. Should read 24 VDC. 24 VDC
2. measure dc voltage at CR4 terminal 1 and 2. should read 24VDC. 24VDC
3. measure dc voltage at R14 terminal 1 . Should read 24 VDC. 24VDC
4. measure dc voltage at R14 terminal 2. Should be between 5-11VDC. 18VDC
5. measure dc voltage at CR2 terminal 1. Should be between 5-11VDC. 17VDC
6. measure dc voltage at CR2 terminal 1. Should be between 5-10VDC. 18VDC

Since im getting more voltage in step 4 on r14 terminal 2, i would assume that (resistor?) is bad? I do get a 40 ohm reading.
Tested most of the resistors and it looks like r10,11 and 12 are blown. i get maybe 1 ohm and it looks like they're 7.5 ohm resistors. Any idea what might have caused this? I don't want to throw money at a new regulator if i have a much bigger issue somewhere.

 

[Guyfang]

OK, first open the control panel. Then look at the A1, (Volt Regulator). To the left of the A1 should be a big honking fuse.

1. Is it there?
2. Have you tested it?

 

[grooving-gru]

Yes, its there and its good

 

[kloppk]

Since the fuse mod fuse is good and you're getting way more than 5-11 volts at R14 & CR2 I suspect it could be due to a few issues.
During that test the set is supposed to be applying the flashing voltage to the Static Exciter which normally causes the 110 to 160 volts across terminals 10 & 11. Since the voltage is way more than 5-11 AND your not getting the 110-160 volts indicates the flashing isn't working properly or possibly not getting to the static exciter.
Issues that come to mind are...
1) Flashing relay K15 isn't closing
2) Loose or bad connection in the wiring from the VR terminals 1 & 3 to the static exciter
3) Broken wire(s) to the static exciter
4) Connection of the wire to the static exciter inside the gen head have come undone
5) Static exciter is burned out

Try this with the set NOT running. Remove the wires from VR terminals 1 & 3. These two wires make their way to the static exciter.
Measure the resistance between the wires. It ought to be around 34 ohms. If it's way higher or open then there is an issue with the flashing voltage getting to the exciter or the exciter is open.

The reason the resistance of the R`10-12 read around 1 ohm is because they haven't been disconnected from the circuit. Those resistors are connected in parallel to the Current Transformer (CT) outputs. What you are measuring is the combined parallel resistance of the resistors and the CT.
I believe the CT resistance is around 1 ohm.
To measure the resistors, you'd need to disconnect the wire(s) going one of their terminals before measuring the resistances.

Also, you may not be aware, but the 804's used two different AC voltage regulations systems. Each system uses unique components depending on if it's a Libby VR system or a TRC system. The systems use different T1 Transformers, VR's, R16 resistors and different front panel potentiometers. Sometimes the components get "mixed" between the systems raising hell with their operation.

 

[grooving-gru]

I tested the resistance between VR terminals 1 and 3, getting an open circuit. I guess next step would be to dig out the diagram to find the connection to the exciter and test the wire first to see if there's a brake. After that i guess ill have to check if the exciter is burned up or not. Sigh.
I know i have the TRC voltage controller. Doesnt look like any one has ever messed with it, no labeling before i bought it.

Edit:
I tested the exciter stator according to 4-21 and disconnected F1 and F2 from TB8. Table 4.3 states exciter stator should be between 28.657 and 38.771. I assume that thousand and not decimal? If so, i'll have to find my bigger multimeter, the little guy will only go up to 2k ohm

 

[Guyfang]

Keep in mind, the Wires do not go from TB8 directly to the exciter. They go through P5/J5 C-Plug. Several times I have found that the P5/J5 was loose, OR pins in the plugs were burnt off. So stand on your head and check that plug. Its on the underside of the control panel. You can use a mirror too. I would test from TB8-1 & TB8-2, to J5-28 & J5-29. Yes its a PITA. Get someone to help. Its much easier. Then from P5-28 & P5-29 to the exciter.

 

[peapvp]

Edit:
I tested the exciter stator according to 4-21 and disconnected F1 and F2 from TB8. Table 4.3 states exciter stator should be between 28.657 and 38.771. I assume that thousand and not decimal? If so, i'll have to find my bigger multimeter, the little guy will only go up to 2k ohm

Assume = making an ass out of u and me….

this is Ohms
28.657 Ohms to 38.771 Ohms

for every day people

28 Ohm to 39 Ohm is fine

 

[Guyfang]

Join the club!

 

[grooving-gru]

I’ve checked p5/j5, looks good.
hooked up to f1 and f2 and got nothing.

 

[peapvp]

Open up the cover on the genhead and let us know what you find

 

[grooving-gru]

thats what i was thinking too. Whats the easiest way to get to it? Looks like half the enclosure needs to come off

 

[peapvp]

thats what i was thinking too. Whats the easiest way to get to it? Looks like half the enclosure needs to come off

That I am not exactly sure off. The sequence is described in the -24 manual
Maybe someone else can assist @grooving-gru

 

[grooving-gru]

That actually wasn’t as difficult as I expected. And I definitely found why it’s not working. I could probably replace the exciter field if i can find a replacement

 

[Guyfang]

This is a not uncommon failure. Most of the time, if you look into the gen set, under the removable cover, Item #5 you should see a small, (or large) pile, just like in your pictures.



MEP-804A Diode Ring Destroyed

Read this thread. Its long, but will help. ALSO, start a parts wanted thread. Someone may have the part you need. This is an easy fix if nothing else is broken.

@Evvy Fesler you out there?