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Thread: MEP 804A no/low voltage

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    Default MEP 804A no/low voltage

    I recently bought an 804A, about 1600 hours, good clean condition, runs nice but it is not generating power, most of the time. But, on at least two start-ups it has generated good voltage, first when i first got it home two months ago, and once last weekend when we started to hook it up to put to work. I have learned that need to hold start switch longer, and have done some testing. It does send 24 volts dc out of #7 on the S-1 switch. I have adjusted the mag pickup on engine flywheel, has 3 volts there and at the control box. The under voltage fault light comes on at startup. No obvious loose connections at output box. The voltage meter on control panel shows around 25 volts, my meter on contactor in output box shows 14 v. On the occasions when it has worked it has shown 208 volts on all three legs on the panel meter.

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    Unplug the A2, (fault Indicator)

    Start it up.

    What happens? Start? Run? Make power?

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    Working on other stuff today, but got back to this tonight.

    OK, did that Guyfang. Starts normal, still low voltage, but now the circuit interrupter indicates (by the light) that it is closed when I move switch. Still shows only 25 volts on meter, my tester shows same on contactor at L1-L2, L2-L3, etc. on both sides. Previously i was checking each to ground and getting the 14 v reading (still do this time too)

    I am wondering if i should start doing diagnostic tests on governor, voltage regulator, etc. that are described in the technical manual.

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    4 Star General Guyfang's Avatar
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    Should not be a governor problem. You are not getting excitation voltage to the exciter coil. Hence you only get the 25 volts from inductance.

    The first thing you need to check is the volt reg system. Here is the story. Back in the day, there was a series of components that the Libby company made to control the AC volt regulator system.

    Then along came the TRC company. They made a replacement AC volt regulator system for the gen sets.

    BUT, they are not compatible. If you have a pure Libby system, and install even one TRC part, it wont work. I have tried to attach the list of parts by manufacturer, but am unable to do so. I am sure I have up loaded the info in the TM forum, but will send you the list by other means. You need to look at each part, and see if its a Libby or TRC system. And not mixed.

    EDIT: OK, so it did upload the list. Click on the black square and it will download.
    Attached Files Attached Files
    Last edited by Guyfang; 09-19-2019 at 02:40.

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    I have one a customer shipped me that was a nightmare for him. Wiring wrong, mixed 400 and 60 hz parts. Came out of Tier 2 reset and has 6 hours on it! Some days I just wonder why some people get to use a screw driver!
    When you put the 2 words 'The' and 'IRS' together it spells 'Theirs....'

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    Is this component compatibility issue consistent with the fact that we have on occasion gotten this machine to generate power without knowingly doing anything different?

    I printed your list guyfang and will take a look later this morning.

    I know i have seen TRC label on the voltage regulator, and i have seen a Letterkenny reset label on side of generator cover.

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    Ok, here's what i found

    TRC volt regulator 19870

    TRC power transformer 17910

    I do not find R16 resistor

    R1 is listed on my schematic as Volt Adjust potentiometer. Maybe this is what your list has as rheostat? This has been changed, the connections aren't original, soldering is messy. The component at R1 is a PEC with two sets of numbers: KU2031S28 0620, RV4NAYSD203A

    Every other component that is easily visible is from TRC

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    For what it's worth:

    When the generator did show good power on the meters for both me and the other guy, we both turned the voltage adjust knob and saw voltage change on the meter.

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    I do not find R16 resistor (Its located on a panel in the control box. The panel has a fuse/circuit breaker and a switch for 50/60 hertz mode. On the back side is the R16. Most folks would never in a million years look there!)

    R1 is listed on my schematic as Volt Adjust potentiometer. Maybe this is what your list has as rheostat? This has been changed, the connections aren't original, soldering is messy. The component at R1 is a PEC with two sets of numbers: KU2031S28 0620, RV4NAYSD203A (clean up the messy solder. I guess the R1 will work. Not sure.)

    Every other component that is easily visible is from TRC

    Now, when you start the set, turn S1 to start, you measured that the S1-7 has voltage. As you start the set, open the control panel. Look at K15. is it activating? It has a small "flag" in it to show you it is operating. The K15 has to activate, to close two contacts allowing the main gen to get excitation. Make sure the relay is working, and that its in its socket right. Also look for loose wires and broken wire connectors.

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    Guy, the K15 relay is working. I couldn't see it well through front opening so I took the top panel off. Its apparent that the top panel has been removed previously. I didn't see any "flag" but it is easy to see it operate from the top. It activates when S1 is turned to start, de-activates when S1 is released.

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