RPM transducer repair

[Flieger]

My RPM transducer/speed switch is faulty. How should I go about disassembly, inspection, and repair? I see that there are a few transistors that commonly break loose from their solder joints due to vibration. Can I just re-solder and then try an RTV coating?

The unit failed the test of raising the rpms to ~2000 with the hand throttle, then manually activating the microswitch while the hand throttle is still raised. The rpms did not fluctuate according to the microswitch. They dropped ~200 after a few momwents and stayed there until I released a little tension on the hand throttle and then pulled it all the way up again. All the while, my friend was pushing the microswitch and releasing it with intervals of a few seconds.

The rpms did not correlate to the microswitch and did not fall and rise again as the fuel was cut off and the idle circuit then catches it on the low end.

The engine is a 2.7 liter RS spec and it was up to temperature when the test was done. It idles a little high when warm ~1500 rpm. It pops through the exhaust on over-run after aggressive driving, in addition to the normal ticking through the intake.

Any info is greatly appreciated.

[Flieger]

BTW,

I have the RPM transducer schematic from the ultimate MFI resource thread on Pelican.

[mhackney]

Flieger,
Take a look at this photo: http://mhackney.zenfolio.com/p508259...111C#880218396 of my RPM transducer. It was pretty obvious when I took the unit out of the case that a section of one of the copper traces had corroded away. After soldering in a jumper (see the series of photos) mine still did not work. Closer scrutiny revealed that several of the transistors were similarly corroded. To me, time is very precious and I needed to get the car back on the road, so I sent mine out to be repaired.

cheers,
Michael

[Flieger]

Thanks for the photos. How much did it cost to have it repaired? I would probably use someone close by, like Dave at TRE, rather than someone in Massachusetts, but I would like to know how much to expect.

[mhackney]

I actually sent mine to Otto's in Venice, CA to be repaired. I believe it was $85. Money well spent since I already had several hours in to diagnosing and really needed to get the car on the road asap.

Michael

[sithot]

Systems Consulting. (out your way)

http://www.systemsc.com/

Tom

[Flieger]

Thanks for the links. I am going to open it up myself and see if it is something simple that I can fix myself.

If I get in over my head, I will send it out.

Cheers

[Flieger]

I disassembled the unit this afternoon. The contacts all appear to be solid.

I am going to clean the copper contacts and the relays. I will warm the solder joints. Hopefully this will get it to work.

I have not seen this type of 2 relay circuit layout in the photos of others' restorations. Anyone have the same thing?

see my parallel post on Pelican: http://forums.pelicanparts.com/showthread.php?t=411623

[Flieger]

Pelican has informed me that this is the 2 stage rear window defroster.

I have no RPM transducer. That would explain the pops in the exhaust on engine braking.

I am looking for a core for Otto in Venice California to rebuild but I may need to just buy a new one.

[Flieger]

Anyone need a rear defroster electrical box?