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Mep 803a no power
- Thread starter Triton
- Start date
- 16,690
- 23,882
- 113
- Location
- Burgkunstadt, Germany
Just because you HEAR a relay klick, does not mean it works right. When the relay, (or contactor) is energised, the contacts are pulled down to engage the corresponding contacts, to pass voltage through. If, (for the sake of this explanation) the contacts DO NOT engage properly, then the proper voltage will not pass through. So do NOT ever believe your ears, ALWAYS check with a multimeter, unless you are like a guy I knew who used his finger. There is not enough money in the world for me to do such a thing.
I rarely make AC measurements phase to phase. I normally check phase to neutral or LO. If I get 120 volts at L1, L2 and L3 to Neutral, then I know I am going to get 240 phase to phase.
I rarely make AC measurements phase to phase. I normally check phase to neutral or LO. If I get 120 volts at L1, L2 and L3 to Neutral, then I know I am going to get 240 phase to phase.
Triton
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- Houston, Texas
Guyfang, I was checking the connections L-1, L-2, and L-3 to neutral. Do I need to disconnect all the wires to K-1 to check the relay? Also when the TM says disconnect and tag a wire how does the Military do that? Is it a numbered alligator tag or a numbered sticker?
lonesouth
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- Tallahassee, FL
painter's tape and a pen works for me.
- 16,690
- 23,882
- 113
- Location
- Burgkunstadt, Germany
Triton,
Lonesouth got it right, if you cant read the wire numbers. I tend to double check the wire numbers with the wire diagrams, as you can shoot yourself in the foot, when someone else has mad a mistake. Example: I once spent 5 days working a problem. Could not fix it. Then someone fresh, showed up. He looked at my tag on the wire, and the wire number, and said "chief, they don't match.) Yep, someone else had miswired it, and I had taken for granted that the wires were right. Boy did I feel dumb. So CHECK before you tag it.
No, you don't need to disconnect all the wires. Get someone to help. The other person holds one probe of your multimeter on N, and you go from wire to wire on K-1. First the input side, then turn on K-1, then measure wire for wire on the output side. Easy! Just keep in mind to be careful!!
Lonesouth got it right, if you cant read the wire numbers. I tend to double check the wire numbers with the wire diagrams, as you can shoot yourself in the foot, when someone else has mad a mistake. Example: I once spent 5 days working a problem. Could not fix it. Then someone fresh, showed up. He looked at my tag on the wire, and the wire number, and said "chief, they don't match.) Yep, someone else had miswired it, and I had taken for granted that the wires were right. Boy did I feel dumb. So CHECK before you tag it.
No, you don't need to disconnect all the wires. Get someone to help. The other person holds one probe of your multimeter on N, and you go from wire to wire on K-1. First the input side, then turn on K-1, then measure wire for wire on the output side. Easy! Just keep in mind to be careful!!
- 2,531
- 2,058
- 113
- Location
- Efland, NC
I would add that many of the voltages you need to check are on the Diagnostic Plug. Use it. Look at the wiring diagram and see what info you can get from the plug. That will be much safer. Don't dig around in the wiring until you have exhausted the troubleshooting options in the diagnostic plug.
Triton
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- Houston, Texas
I checked the plugs on the diagnostic port and they all were within the listed values. I work on checking K-1 this afternoon
Triton
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- Houston, Texas
This is what I found out today, I tested K-1 with the ohm meter and the unit off, there was no continuity on either side of the three contacts.
I started the unit with 120\240 selected on K-8, I test for AC voltage on K-8 and got 24.7 volts on 2 contacts.
K-1 had 24.7 volts on one side of the relay on 2 lugs, I closed the AC interrupt switch and got 24.7 volts on the other side of K-1 on the corresponding 2 lugs
I held down S-1 and got 121 volts on two lugs through K-8 and K-1 down to the lugs L-1 and L-3 and the convenience plug. When I let go it goes to 24.7 on the convenience plug and nothing on L-1 and L-3
When I hold down S-1 with the AC interrupt switch closed, the K-18 relay clicks and applies 24.7 DC volts to the right contact on the relay and that's when I get 121 volts to the lugs. I attached a picture of the K-18 relay to make sure that's what it is
I started the unit with 120\240 selected on K-8, I test for AC voltage on K-8 and got 24.7 volts on 2 contacts.
K-1 had 24.7 volts on one side of the relay on 2 lugs, I closed the AC interrupt switch and got 24.7 volts on the other side of K-1 on the corresponding 2 lugs
I held down S-1 and got 121 volts on two lugs through K-8 and K-1 down to the lugs L-1 and L-3 and the convenience plug. When I let go it goes to 24.7 on the convenience plug and nothing on L-1 and L-3
When I hold down S-1 with the AC interrupt switch closed, the K-18 relay clicks and applies 24.7 DC volts to the right contact on the relay and that's when I get 121 volts to the lugs. I attached a picture of the K-18 relay to make sure that's what it is
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Triton
Active member
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- Houston, Texas
This weekend I'm going to check the wire numbers going to K-18 to see if they are correct, maybe the PO put something back wrong. I don't know why they would be messing with that but they did wire the alternator wrong so you never know.
Triton
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- Houston, Texas
Well, I was able to do some testing today, all the wires to K-1 are correct. I disconnected the wires to K-18 and I can hear K-1 clicking when I hold down S-1 and I get voltage. I tried looking at the schematics to see which wire goes back to the start circuit but I am not getting it. After the engine starts what keeps K-1 activated after you close the AC interrupt switch? I'm lost again!
- 2,130
- 3,497
- 113
- Location
- Pepperell, Massachusetts
It's a "latching" circuit created by K1, S5 & K8. It has to do with the switch contacts in K1 terminals 11 & 12.
After the engine starts and oil pressure is up K1 terminal X has 24 volts supplied to it. When you toggle S5 to CLOSE S5 terminals 5 & 6 connect momentarily connecting K1 terminal Y to ground causing K1 to close and closing K1 contacts 11 & 12. When you release S5 a path from K1 terminal Y to ground is created via S5 terminal 5, CR 3, S5 terminal 2, S5 Terminal 3, K8 OL, K8 SC, to K1 terminal 11, to K1 terminal 12 to ground. This path keeps K1 activated after releasing S5 from the CLOSE position.
When you toggle S5 to OPEN you break the connection between S5 terminal 2 and S5 terminal 3 breaking the ground path causing K1 to open.
K8 OL and K8 SC are in the path so that if the fault logic detects an overload or a short circuit condition is will cause K1 to open removing power from the lugs.
Based on your test results in most of post 16 & post 28 it appears your voltage regulator is bad.
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Triton
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Thanks Kloppk, that is a lot going on, is there a procedure for checking that or should I just start checking voltages on the K-1 contacts? I'm going to double check the voltage regulator again!
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- 2,130
- 3,497
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- Location
- Pepperell, Massachusetts
From your tests K1 seems to be operating properly.
When you CLOSE the contactor K1 you get ~24 VAC at the lugs AND the convenience outlet with S1 in the RUN position. You get 120 VAC at the lugs and convenience outlet with S1 in the START position.
Regulator operation.... assuming no wiring issues...
With S1 in the START position you are flashing the generator because a flashing DC voltage is supplied to G1 terminals F+ & F-. What should happen upon flashing is the Quad winding should output 67 to 85 VAC across G1 Q1 & Q2 proving power to the regulator. The regulator samples the 120 VAC voltage at it terminals 3 & 4. Given the Quad winding AC power, the 120 VAC sense inputs and the R1 resistance setting it suppose to then output a DC voltage to it's terminals 5 & 6 providing a Field voltage to the generator causing it to continue to output 120 VAC once you release S1 from the START position.
I'd suggest carefully re-doing TM section 2-27 to check the regulator.
When you CLOSE the contactor K1 you get ~24 VAC at the lugs AND the convenience outlet with S1 in the RUN position. You get 120 VAC at the lugs and convenience outlet with S1 in the START position.
Regulator operation.... assuming no wiring issues...
With S1 in the START position you are flashing the generator because a flashing DC voltage is supplied to G1 terminals F+ & F-. What should happen upon flashing is the Quad winding should output 67 to 85 VAC across G1 Q1 & Q2 proving power to the regulator. The regulator samples the 120 VAC voltage at it terminals 3 & 4. Given the Quad winding AC power, the 120 VAC sense inputs and the R1 resistance setting it suppose to then output a DC voltage to it's terminals 5 & 6 providing a Field voltage to the generator causing it to continue to output 120 VAC once you release S1 from the START position.
I'd suggest carefully re-doing TM section 2-27 to check the regulator.
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Triton
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- Houston, Texas
I was just thinking, one of the problems I had with this 803 was it would not shut down. We found out through this forum that the PO had wired the alternator wrong causing it to back feed S-1. Do you think that that could have fried the voltage regulator?
Triton
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- Houston, Texas
Well I tested the voltage regulator again and this is what I got!
H- voltage 8.00 VDC
J- 85.7 VAC
L- 122.0 VAC
N- 0 to 5,000 ohms
So I would deduct from the TM my voltage regulator is bad, the good news is the potentiometer seems good!
My next question is can the voltage regulator be repaired?
If not where should I look to purchase a new one or is there any other options?
H- voltage 8.00 VDC
J- 85.7 VAC
L- 122.0 VAC
N- 0 to 5,000 ohms
So I would deduct from the TM my voltage regulator is bad, the good news is the potentiometer seems good!
My next question is can the voltage regulator be repaired?
If not where should I look to purchase a new one or is there any other options?
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- 2,130
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- Location
- Pepperell, Massachusetts
Yes assuming the defective component(s) inside A1 can be identified.
It just a basic printed wiring board with "thru hole" components soldered into it.
Looks like this inside..
Triton
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From what I have read is it the bridge diodes that need to be checked? What else should I look for?
Thanks for your help!
Thanks for your help!
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Triton
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- Houston, Texas
I pulled the regulator today and tested the diodes and some resistors they all seemed good. Nothing looks or smells burnt, can anybody suggest anything else I can check on this board? Still don't know where to purchase a new regulator, anybody have any suggestions?
- 16,690
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- 113
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- Burgkunstadt, Germany
Partner, look up the NSN, and plug it into your browser.
The potentiometer rarely goes bad. Mostly someone breaks off a wire.
The potentiometer rarely goes bad. Mostly someone breaks off a wire.
Haoleb
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- Raymond, Maine
You might want to check those two transistors or voltage regulators that are on either side of the board. If you punch in the number on the chip you can get a data sheet and once you know what it is you can find out how to test it... Sometimes components will test bad in circuit but when removed are good.
I'd get the part number for that regulator and watch ebay for a replacement.