MEP-803A Low Voltage

[jmpratt]

Ok, next question. I have a 1997 MEP-803A that was reset in Sep 2011. It has 440 hrs. It'll start up and idle at 60hz but the output voltage is low. I have it set to 240V/single phase and the voltmeter needle is pegged to the left (voltage not high enough to make the scale). My DMM is showing 60.2 HZ and 24 VAC at the aux outlet.

I'm thinking something's up with the DC exciter voltage? I'll check the diagnostic connector readings (between F and J) tomorrow. Any quick advice?

-Jason

 

[Guyfang]

What do you mean by idle? There is no idle. It is supposed to run at normal speed all the time. You mean running at no load, 60 hertz?

You don't need to use the diagnostic connector, measure direct at the A1. When starting, if you hold up the S1, and keep it up, do you get 120 volts on the meter? Then it drops off when you let S1 go?

 

[Bmxenbrett]

Aux outlet? Are you talking about the nato plug on the side?
You need to measure the output voltage at the large lugs in the left lower pannel while looking at the gauges. Make sure you close the main contactor switch too. The light above it should be on.

 

[Guyfang]

I am pretty sure he ment the 120 volt outlet. He mentioned getting 60 hertz and 24 volts VAC. I would bet that if you switched the Emma to DC, it would have said dc

 

[jmpratt]

Yes, I meant the 120 volt outlet. Also, yes, by idle I mean no load. It runs right at 60 Hz, so it's not under speed. I will try your suggestions this afternoon.

 

[Bmxenbrett]

Thats the convenience outlet. Theres a breaker for that.

 

[jmpratt]

More diagnostic info: The convenience outlet reads 24.75 VAC, 0 VDC, 60Hz. Voltage is the same when S1 held up or when released. I have the unit set to 240V/1Phase. Voltage between L1 & L3 is 48.5 VAC. DC exciter field voltage (pins J&F on the diagnostic connector) is 0 VDC. 0 VDC on pins U & V (measured to ground). These are output to DC circuit breaker and voltage across output circuit interrupter coil, respectively.

 

[Guyfang]

Mesure on the A1, during startup. Pins 5 and 6. 6 is positive. are you getting 24 volts DC?

Do you have the Quad circuit mod?

Is the fuse good, if you have the mod?

 

[jmpratt]

I will check for the mod and let you know.

Also, speed sensor is disconnected. I assume that will keep the circuit from flashing since it never senses the unit rotation?

When connected, the starter cuts in and out before unit gets to operating speed. I'll swap in another controller (left most "relay", correct?) to see if that makes a difference.

 

[jmpratt]

Yes, it has the quad circuit mod. Fuse is good, not blown. A1 is at 7.0 volts during start, 0 volts in run.

I reconnected the speed sensor the problem in the fuel solenoid is weak on won't always stay open in run. Right now I'm using a string to hold it open. It shows good voltage across the hold open coils. Probably a bad solenoid.

 

[Guyfang]

By speed sensor, you mean the magnetic pickup? If so, it NEEDS to be hooked up, for the excitor to work properly. You need to check it, to see if its working right. To test it, disconect the two connectors, use your multimeter, set on AC volts, to mesure across the two connectors. Have someone else use the S10 switch to crank over the engine. What you want to see is 3 volts AC on your meter. The book says between 2.5 and 3 volts. 3 is best. Pull the mag pickup out, check it for metal filings, trash and such on the end of the pickup. If there is about a million feet of real thin copper wire haning out of it, toss it and get another. If the end of its ground off, get another. If its in good shape, screw it in until it hits bottom. Back it off 3/4 turn. Tighten the locking nut hand tight. mesure as I explained before. 3 volts AC is what you want. if is a little low, loosen the locking nut, then screw in in a cats hair. Test again. continue untill you have 3 volts. DO NOT GO ANY FARTHER!!!!!!!!!!!!!!! Or you will grind off the end of the pickup. The mag pickup sences the correct engine speed, locks out the starter, and allows the S1 switch to send voltage to the excitor. If this dosnt make sence, its also in the TM. This is simple, as loong as you pay attention. Take your time, and you wont destroy the mag pickup. 99% of the failed mag pickups, failed because someone screwed them in too far.

 

[jamawieb]

You've got to have everything hooked up correctly for these machines to run right. If you don't have the speed sensor hooked up then the exciter will never fire for the generator. That would be the reason your only getting 24 volts. I suggest you start from the beginning and hook all your wires back up and take any things you added off. Usually when the fuel cutoff solenoids fail, they fail with the initial holds, i.e. they can not hold the lever back when they are first activated.

 

[Guyfang]

Are there any other things unhooked?

 

[jmpratt]

Nothing else unhooked. When I crank (S1 to start), 7 volts on pins 5 & 6 on A1. Drops to 0 volts when S1 released to Prime/Run. I haven't got a chance to check the voltage of just the magnetic pickup, yet. Will probably get to that on Thursday.

 

[Guyfang]

When you have the S1 in the start position, you should have 24 volts on pin 7, of the S1. Do you? Because that's where it all starts. If that voltage is not present, no excitation can happen.

Did you check, test, inspect and adjust the MPU, (mag pickup)?

 

[jmpratt]

Just checked pin 7. No voltage on 7 while cranking. Should I check K15?

 

[jmpratt]

Just checked the magnetic pickup. I pulled it out and it looks good. No damage. Reinstalled it per your instructions and it's showing 2.7 VAC.

 

[Guyfang]

Just checked the magnetic pickup. I pulled it out and it looks good. No damage. Reinstalled it per your instructions and it's showing 2.7 VAC.

thats good enough to make it run.

If you have no voltage on S1-7 while cranking, your S1 is bad. What type S1 do you have? If you don't know, take a picture and post it.

 

[jmpratt]

Checked S1-7 again and it has about 20 VDC. I think my meter leads were loose last time. Anyway, I can trace the voltage from S1-7 to K12-8, K12-2 to K16-9, but nothing out of K16-3. I checked this with the starter solenoid disconnected so the engine wouldn't crank which maybe messing up the control system. I noticed that K16 closes when S1 goes to Run which would disconnect K16-9 from K16-3. Is K16 supposed to open during crank?

 

[kloppk]

Here is a thread that has a great color coded schematic thanks to the hard work by DieselAddict
See last post for latest version.
Use the "layers" feature in Adobe to view.
https://www.steelsoldiers.com/showt...Drawing-restoration/page5&highlight=schematic