First MEP 803A, fix up help

[rickf]

"When I was putting it back, some of the wires looked weird so I checked all the connections and a couple of wires were out of place. A couple were on jumpers so they did not really matter, but I did find that 5 and 9 were reversed. I believe this put L1 and L3 load readings in series instead of parallel, which was why I was getting almost double the current reading that I should have.
SO, when I fixed those, the load gauge now reads correctly!"
Good catch on these wires. Tells you someone has been in there before and did not get things back as they should. Time to sit down with the diagram and your Deoxit and start cleaning and paying attention to where each and every connection is supposed to be and where it actually is.

 

[nextalcupfan]

Thanks for the replies.
I just followed the TM guides on testing the gauges. I haven't worked on these before, so I wanted to post my findings and get a feel if that was normal or not. Sounds like is is Acceptable for these units.


I opened up the interrupter and the seal looked good and the contacts were pretty clean. I brass wire brushed them clean and reassembled.
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I could not find much info on the shunt part, but it looks original, so I am going to assume it is ok.
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I got a can of deox/electronic cleaner and sprayed down that phase/voltage switch (S8 I believe?), and the S6 switch for the measurements. Moved them around and sprayed some more. Hopefully that cleaned them out.


So, I could not find any replacements online for this model 19260 frequency transducer, so I figured I would take a try at fixing it. I am not great at electronics repair, but I know some.
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After desoldering, testing, and re-soldering way too many parts (had to test them out of circuit), most checked out fine. A couple of resistors had drifted a bit from spec, but not too bad. I decided to mess with the two potentiometers and hope that would do some good. I couldn't see all the traces to the pots, but It looked like they may adjust the 555 timer IC, so I figured they might be a fine tuning calibration.

Well, the output jumped all over the place when I touched those! Seems like there was wear or corrosion inside the pots somehow. I exercised them a lot, then adjusted them close to where they were originally and was able to get it working! While plugged it into the wall, I calibrated it to 100uA DC with the pots. The left one seemed to be more of a fine tuner, with the right being coarse. But I am not sure so I tried keeping them both close to the original marks.
I haven't tried it on the generator yet, but it seems to be good now. It is a little worse for wear thought, lol.
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So, yea I think people could try to repair the Frequency Transducer 19260.

1. If yours is just out of spec, I would check the two grey adjustment potentiometers on the front. Mine were messed up inside and needed to be exercised. I also had to fine tune it a little, probably due to resistor drifting or the pots.

2. If you have no output, and nothing is obviously burnt, I would check the fine wires on the 120V/16V transformer leads. One may have just broken loose. Don't ask me why I had to figure that out, sigh...

Hope this helps someone.

Going to do the oil gauge mod next. And I ordered a new thermostat for when I flush the radiator. Still working on it.

Thanks so much for this, my freq meter has been off by about .7-1hz ever since I got my unit. I've been tearing my hair out trying to find a decent replacement that isn't a million bucks.
Now that I know the transducer has those pots that get dirty I can clean them then "re-calibrate" it to match my Fluke DMM and Oscilloscope.

 

[Pirotess]

Thanks so much for this, my freq meter has been off by about .7-1hz ever since I got my unit. I've been tearing my hair out trying to find a decent replacement that isn't a million bucks.
Now that I know the transducer has those pots that get dirty I can clean them then "re-calibrate" it to match my Fluke DMM and Oscilloscope.

Glad it helps!
You need to carefully drilled out the rivets. If you go too far in you may hit the circuit board. I believe they were 1/8" hole rivets if I remember correctly.
Next, I had to desolder the screw posts so I could get the rivet remnants out from under the circuit board. If you don't have that problem, you can just adjust the pots without unsoldering anything.
Hooking it up to a wall plug and calibrating it to 100uA DC output with my fluke 87 worked well for me.
Once you are done, a dab of silicone or hot glue on the pots keeps them from moving due to vibration.
Install new rivets and that's it!
It has been working well for me so far.