MEP-002a overvoltage, bad transformer

[dmistretta]

Hello,
I'm new here and have learned tons from lurking and researching over the past 2 months.
I recently bought 2 MEP-002a units from Warner Robins and it's been a learning experience.
The good news is I already have one working 100%.
The bad news is, the other I am having some issues with. After a bit of plinking around was finally able to get it started where it immediately produced 160ish volts with the voltage knob having no effect. I am getting 60Hz spot on, or whatever I set the throttle to. At first I was thinking the VR was bad, but a visual inspection didn't show any blown components. I followed the TM and found out that the Current/Voltage Transformer in the AC Output box (listed as CVT1) seems to be bad. Using my cheapo Harbor Fright meter the resistance is relatively right (or at least all of them are the same amount off which shows my meter is not super accurate) on all tests except for the control C1-C2, which shows as open. Further inspection of the transformer shows that it's cracked in 2 places across the top.

I'm looking for a replacement but am having issues finding what I need. Does anyone have a source for this part?
I've also done a little reading on replacing the whole VR circuit with an aftermarket by flight systems, but am finding little information there also. Anyone have experience with replacing it? I'm a bit overwhelmed by the amount of wires in there and don't even know where to start.

I appreciate any help that anyone can give me.

 

[Speddmon]

Your problem is the AC Voltage Regulator, not the CT/CVT assembly. The CT/CVT assembly is used primarily for condition monitoring. The voltage issue you are having is a classic sign of a bad output transistor on the VR board. Easy fix if you can do anything at all with electronics. The transistor at issue is the largest one on the board. It will not show physical signs of damage most likely.

 

[dmistretta]

Thanks for answering so quickly. I'll take a closer look at the transistor. Since I have 2 units I will probably try a board swap and see if the problem follows the board.

What will the symptoms be of an open on C1-C2 on the CVT? the one on the 'bad' mep still shows an open across them. The one on the 'good' one shows 9.x ohms. Is this something that will need to be addressed?

Your problem is the AC Voltage Regulator, not the CT/CVT assembly. The CT/CVT assembly is used primarily for condition monitoring. The voltage issue you are having is a classic sign of a bad output transistor on the VR board. Easy fix if you can do anything at all with electronics. The transistor at issue is the largest one on the board. It will not show physical signs of damage most likely.

 

[Jasonz in MO]

Dmistretta,

I have the exact same symptoms. ~160vac at the 120vac service sockets, voltage control has no effect. I replaced Q3 output transistor but did not fix it. Today I checked the resistance of the CVT1 transfomer and my control windings C1-C2 are also open. Should be around 9.6 ohms. The output of the VR board and transistor controls the generator output voltage by controlling the current through these control windings. From what I have learned and can read on the schematic CVT1 is a required component for voltage regulation.

Were you able to find a source for this transformer?

Jason

 

[leedawg]

Contact William Delk at Delks navy army surplus.
Located in N.C.

Super nice guy.


They will have every part you can ever want for this machine.
336-629-0991