MEP 003 VR repair.

[metalworker393]

Hello and how is everyone, Have a quick question. I have my 003 that quit making power (like 6 volts) so I swapped out the vr from my 400 hz machine and put the jumpers in as per the TM. Now, will the voltage have to be calibrated on the vr I put in or should it already be properly adjusted? I havn't started it yet. next If it makes power then obviously it was the problem, but is there anyone out there repairing these? the transistors at CR5, 7&8 look like they are exploding. Where the wire comes in and out of the transistor there is a bunch of white material coming out. appreciate any input metalworker393

 

[gimpyrobb]

Try speddmon, pretty sure he has fixed some.

 

[Triple Jim]

Configure the jumpers as shown in the diagram of the TM for 60 Hz use and try it. If the voltage adjust pot is off, all it will do is skew the range of the panel pot, so you can center the panel pot and adjust the board's voltage pot to reach the correct setting. Don't worry about the sensitivity pot yet unless the voltage is not stable.

The transistors are Q1, Q2, and Q3. Are these the parts you mean? The CR designation is for diodes, so maybe these are the parts that you describe as looking like they're exploding.

 

[metalworker393]

hello jim how are you, looking at the board q1 and q2 are in the upper right had corner and q3 is the one with the two bolts through it. on the left side of the board, next to terminal 14a little transistor or what ever you call it, its very small and shows cr5 to the right. next to terminal 16 same looking part and to the right it shows cr7 . next to terminal 17 same looking part and shows cr8 and looking at it right now cr9 is going too. Jim which is the voltage pot? are you referring to the rheostat as the panel pot? which is the sensitivity pot? Thank you for your time and help metalworker393

 

[Triple Jim]

hello jim how are you, looking at the board q1 and q2 are in the upper right had corner and q3 is the one with the two bolts through it. on the left side of the board, next to terminal 14a little transistor or what ever you call it, its very small and shows cr5 to the right. next to terminal 16 same looking part and to the right it shows cr7 . next to terminal 17 same looking part and shows cr8 and looking at it right now cr9 is going too. Jim which is the voltage pot? are you referring to the rheostat as the panel pot? which is the sensitivity pot? Thank you for your time and help metalworker393

The CR devices are diodes. They are very inexpensive and simple to replace. You can use any of the 1N400X series. Even the highest voltage version, the 1N4007, rated at 1A and 1000V is a few cents at Mouser. You can test them by unsoldering one end and using the diode test function of a modern multimeter to see if they conduct with the + meter lead on the unbanded end and the - lead on the banded end. They should not conduct in the opposite direction.

If you have regulator board 72-5020, the voltage adjust pot is R17. If you have 72-5338, it's R12. Yes, the front panel rheostat and the voltage adjustment on the board work together, so you can set the front panel knob in the middle of its range, and adjust the pot on the board for 120V if you like.

Obviously the other pot is the one I referred to as the sensitivity pot. It's really the transient response adjustment which optimizes the regulator's response to sudden changes in load. You probably won't need to mess with it, but the procedure in section 6-6 on page 6-8 of TM5-6115-585-34 tells how to set it for best operation.

 

[metalworker393]

How is everybody today, Okay Jim this one is for you. I switched out the vr from my 400 hz machine and set the jumpers up as per the tm. I decided to fire the machine up and see how it is. I had the machine running and was only getting 7-8 volts on L0-L1 and L0- L3. no real change in voltage and when I switched the multimeter to frequency I was able to see a change as I sped up and slowed it down. Yes the voltage selector was set at the 120/240 position. after that I decided to look at the generator head so I took the cover off and the rotating diodes and bracket are corroded pretty bad. Think that has anything to do with it? any other suggestions? anyone else want to chime in go ahead. this machine was making power a year ago and then just stopped, thanks metalworker393

 

[Triple Jim]

Bad rotating diodes could cause the problem, as could a bad CVT1, or one or more bad diodes in the rectifier board A4. Of course any of the wiring or connectors that carry field current from CVT1 to the generator could be the problem too.

J12 is on the back of the cabinet that houses CVT1, the output lugs, etc., and carries field current to the generator. You might check to be sure the contacts in that connector are clean.

The resistance between X1 and X2, between X2 and X3, and between X1 and X3 on CVT1 could be helpful, too, if nothing else turns up a problem. I hope other will add to this, because I'm sure I haven't thought of everything.

 

[Munchies]

Make sure the field flash circuit is in working order, and flash it good. Check the capacitor on the bridge rectifier in the back of the 'reconnection box' as well.

 

[Triple Jim]

Just a minor point, but the rectifier board (A4) has one resistor that should measure about 50 Ohms, and six diodes. The resistor limits the flashing current, so you're right, it has to be intact.

 

[metalworker393]

Good day and how are you all? Okay I did hold the start switch in the start position for about 20 seconds after the engine was running. I did not repeat it though. How do you test the flash circuit to make sure it is working and where in the TM's is it described? which is the capacitor on the bridge rectifier? (a4 board) and what is the procedure? As jimc suggested I am also going to clean the grounds as well. I was thinking of running a no 6 wire from one of the bell housing bolts to the ground lug to make sure the gen head has a ground. would there be a problem with that or is that not recommended?

 

[Triple Jim]

As I said ^ it's a resistor, and it's the obvious big thing that's not one of the six small diodes. To see if the flashing circuit is working, you measure the voltage on the exciter field when you're cranking the engine. You could do that at J12, which is the connector with two wires on the back of the reconnection box. You'll probably need to take the plug apart so you can get to the back of the pins while it's plugged in. I suppose you might be able to measure it right at the exciter, if you take the cover off the end of the generator.

My 003A has the flash circuit supplied through the starter disconnect switch, so once the engine starts, holding or moving the master switch back to "start" does not flash the field. This is shown in the 003A schematic as well, but I don't know if all the units were wired this way. If yours is like mine, then if you want to try flashing the field again, you have to stop the engine and restart it.

 

[metalworker393]

Okay, I checked the resistor on the A4 board and my meter is reading 54.6 - 54.7 , suppose that's good? As far as the flash circuit, I tool the plug off of the j12 receptacle set my meter to check for continuity on the pins and did get that. If the j12 plug goes back to TB3-5 and TB3-6 could I get longer screws and a jam nut for those two positions screw the screws in jam the wire connections with the nut and hook my alligator clamps on my meter leads to the longer studs? if so that would allow me to read my meter while cranking to check for voltage, eh?

 

[Triple Jim]

I was thinking you could unscrew the strain relief and back shell from the 3-pin connector J12 and just hold the meter probes on the back ends of the two active pins, but I don't remember if that's easy to do on that type of connector. Anything that allows you to read the voltage on the exciter field is what you're looking for.

 

[metalworker393]

Okay, just went outside and took a reading at TB3-5 & TB3-6 . I didn't preheat the engine just put the probes on the screw heads and and started cranking. I was reading 1.4,2.5 2.3 volts before the machine started. After starting I was getting about 5 volts on my meter. Is this normal? I also flashed the machine for 20 seconds while it was running. L0- L3 & L0- L1 now reads 10 volts from 6 1/2-7 volts.

 

[Triple Jim]

The exciter field resistance is 36 ohms. With a 24V supply in series with a 50 ohms resistor, the field voltage should be around 10V during flashing. As I said above, my 003A will not flash the field once the engine is up to speed, no matter how much I hold the switch in the start position. I have to stop the engine and restart if for another go at flashing.

If you're not getting flashing voltage at the exciter field, you should probably see if you're getting about 24V at terminal 6 of diode board A4 during cranking.

 

[Munchies]

Jim corrected me, it is a large resistor on the board. Dont post in delirum......
They do sometimes burn up. I have a couple toasty ones here.


Edit..I see you already moved past this.... Good, kind of a pain to take that out anyhow

I would check at the exciter as jim says. It is the end of the circuit, and will save time in the long run.

 

[metalworker393]

All right, so if my machine is set up like yours the only real way to flash it good would be to disconnect the fuel supply at the ip, disconnect the electrical plugs on the pumps and crank the **** out of it. Is there any way to bypass the starting sequence and not crank it yet send current to the gen head? Isn't flashing the machine have something to do with re magnetizing the some inner component? Kinda like when you wrap a coil around a screwdriver end and touch it to a battery so you can magnetize it. Problem is the engine on this machine starts great so I don't get much time cranking before it starts. I guess I could also try disconnecting the oil sender. Wouldn't that keep it from starting?

 

[Triple Jim]

I don't think it is necessary to flash the field for an extended time, but it is necessary that it gets flashed during starting. Make sure you see something like 10V on the field while you crank. If you do, it's time to move on to the next possible problem.

 

[Munchies]

For a test, you could just apply voltage to the exciter. I dont think a 12v battery would be over doing it.
If you see voltage there, then yes move on, and try the diodes next, they are not too bad to check or replace.

 

[metalworker393]

Hey guys, I checked the voltage at TB3-5 & 6 yesterday one more time. I was still only getting like 3.5 -3.8 volts. I did not get to check A4 T6 for 24 volts, I will try and do that today. You say to apply 12 volts to the exciter field, that would be through the J12 connection if I understand you correctly? The diodes, are you referring to the rotating diodes? If so jimc emailed me the p/n's and where to buy them. The heat sinks are corroded (oxidized) pretty bad. Not through but not healthy either. thanks metalworker393