Need T2 for MEP-003a

[Isaac-1]

Well today I found the source of the voltage control problems on my new to me MEP-003a, it seems someone wired T2 up backwards with the X1/X2 wires goes to H1/H2, and vice versa. This seems to be a simple enough step down transformer, but I can't find any specs online, so I am therefore asking if anyone has a source for a replacement, or know the rating and ratio so I can find a drop in replacement. Thanks Ike p.s. Does anyone that understand the VR circuit better than I do have any thoughts on implications of T2 being installed backwards?

 

[Triple Jim]

It's a step-down transformer that supplies a voltage signal to the regulator board to tell the regulator about the generator output voltage. Wiring it backwards makes it a step-up transformer, attempting to apply a very high voltage to the regulator board and causing a very high current and associated heating of the transformer. The good thing is that the regulator would have tried very quickly to reduce the generator output and may or may not have saved the transformer and itself. If it's not obviously burned, you might try wiring T2 correctly and seeing if everything works properly. If not, shut things off quickly and begin the troubleshooting procedure.

I was able to pick up a NOS T2 for my test/calibration rig off the web at a reasonable price.

 

[Isaac-1]

No such luck, the transformer is fried, visible chucks missing and open circuit on both sides. Just for clarity I am talking about the transformer with 4 wires going to it 72-5004, it seems the TM refers to this as T2 in the cabinet and T1 in the test bench circuit. Ike p.s. Jim, do you happen to recall where you found it online, I find lots of links to the usual NSN click for quote sources only

 

[Triple Jim]

Yes, I thought you meant the non-center tapped one. I just checked, and the source of my transformer is not listing any more for sale. If you can't find one, I'd be happy to take the cover off my test rig and measure the output voltage. Then you can just get a generic replacement. If you have a running 002A or 003A you can probably beat me to it. With the adjustment range of the regulator's on board pot and the front panel pot, the output voltage of that transformer shouldn't be terribly critical, and the current requirement is minimal.

I suppose the reversed transformer may have blown the regulator board, possibly in the flashing during startup. Then the blown board wouldn't have regulated the generator output, so the transformer burned.

 

[Isaac-1]

The first thing I did was swap boards with the spare one I had bought from you, before running through the flow chart (did not have the manual with me at the generator), so I don't know the condition of the original AVR board yet (voltage was high). I think I will probably set up a test bench and check it if I can find a T1 and T2 cheap enough, already suitable pot and variac. If no one shows up with the specs, or a source I will probably pull the T2 from my MEP-002a and test it for output level. Ike

p.s. I am also a little worried about the CVT, its C windings were reading about 20% off, others were in the 10% +/-

 

[Triple Jim]

Just run your 002A and measure the secondary voltage. The primary should be 120. The current rating is small, well under 1A. I was not able to find T1 at a reasonable price, so I used a generic multi-tapped transformer. You can also measure your T1's secondary voltage while the generator is running. That one needs to be able to put out a good part of an amp in use, since it supplies the control current for CVT1.

If you decide you'd rather not be bothered setting up the test rig, I'd be glad to check and adjust any of your regulator boards if you cover the shipping cost.

 

[storeman]

Ike,
I have one 72-5004. E-mail me jerry@queenscreek.com
Jerry

 

[Isaac-1]

It is looking like this is a 4.5:1, 31.1VAC secondary at 140VAC primary according to the specs, so I suspect any common 120VAC to 28VAC transformer of about the same size should work, if I can't find an exact match. Ike

 

[storeman]

Ike,
BTW: I tried to PM you but your box is full.
Jerry

 

[Isaac-1]

will empty did not realize

 

[Isaac-1]

Just to let any lurkers know, I bought a replacement T2 from Jerry, installed it today and now get good voltage, so on to the more trivial (hopefully) problems, frequency meter, glow plugs, etc.


Ike

p.s. I can see how someone might make the mistake and install this transformer backwards as the circuit diagram on the top of the control box shows the X terminals on the left and H terminals on the right, opposite their traditional layout arrangement. I suspect this was done for logical flow reasons, but it does give at least a bit of an excuse to whoever before me that worked on it.

 

[storeman]

Ike,
Glad it worked.
Jerry

 

[Ray70]

Hi Ike, Do you know what is causing your Hz meter issue? Bad meter or transducer?
One of my units has a transducer that does not like vibrations. works fine on the bench but any vibration or shock to the transducer sends the gage haywire!
Friday I received a panel mount digital Hz/volt meter I found on e-bay for $19. Made an adapter plate to mount in place of the gage and a harness to hook it up to the TB where the transducer used to attach. I hope to test it tonight. If you have a similar problem I can give you the particulars on what I used and I still have my mill programmed to cut and drill the adapter plate if you want one.

 

[Isaac-1]

Ray, thanks for the offer, but I don't know yet, it was getting dark when I managed to get around to the generator project last night, too many other must do projects came up, like the door knob on the back door of the house breaking, etc. It will probably be Wed or Thurs before I can get back to the generator project, maybe even next weekend.

Ike

 

[storeman]

Ray70,
I installed one of those $19 wonders about a month ago and it works fine. If I recall correctly, I took the feeds off the voltage meter and taped off the leads from the xdcr.
Jerry

 

[Ray70]

Hi Storeman, I had a minute to play with the meter late last night. I had disconnected the transducer at the TB and taped off all the unused wires, reconnected the meter at the same points on the TB (12 and 13 if I recall ) expecting to see 120V at the meter, but got nothing. Maybe I have a wire reversed or something.... it was late at night! But... I think running it off the volt meter as you did and getting 240V at the meter sounds like a better plan. Did your meter fit into the hole from the old Hz meter? I had to just file the corners off the back of my meter a little so I didn't have to touch the control cubicle door at all. Thanks for sharing your install, I need to work on these things during the day instead of midnight.... why wouldn't I have jumped off the volt meter in the first place?

 

[storeman]

My meter was rectangular and I had the cut an aluminum disk and put a rectangular hole in it to mount the meter. You will get 240 when you run 240 and 120 if you switch to 120 only. Please list a source if you found a digital with a correct size round back plate. We could all benefit from that.
Jerry

 

[Ray70]

Hi Jerry, my meter is rectangular too, made the same round disc with a rectangular cut out. I had to file the corner of the meter just a little to get it to fit through the round opening fron the original meter. I hooked it up like yours and it works good. Apparently I disconnected a wrong wire on my first attempt wiring it to the terminal block because when I started the machine the volts were at 300V, I reconected the 2 wires I took off terms 12 and 13 and everything is good now. Had time to load test all 3 units yesterday. Think I need to look at the govenor on 1 of them, Hz swing from no load to full load seems excessive, the other 2 work good, but that's another thread...

 

[storeman]

Glad it worked well for you. Yes, does sound like a governor issue on the 3rd one.

 

[Ray70]

Jerry, I bumped up an old thread from last December where you were one of several guys having similar Hz droop issues. ( don't want to take this thread too far off subject ) Please check it out and let me know if you got yours fixed and how you solved it.
Thank you
Ray.