tachometer failure

[erubin]

1982 300D
For several years I've been wedging a cigarette butt under the tachs amplifier cap. The extra pressure allowed the tach to function a few weeks at a time. Recently it stopped working all together even with a new butt or more.

I dug out the sealant on the back side of the amplifier's circuit board and found two solder cracks at component through holes. The board didn't look burnt. i resoldered all the solder points but tach still not working.

Before I condemn the amplifier (where do you get a replacement anyway?) is there a way to test the pickup on the front of the engine? Can it be tested with a voltmeter set in AC volt mode. Will it generate voltage even if the amp is no good?

I cleaned the pickup, it was really grimy with a groove in it where the damper pin passes. The pin on the damper looked shinny because it was rubing the grime on the head of the pickup. the pickup bracket is not bent and the pickup is securely attached to the bracket.

[toomany MBZ]

You may want to try working on the female aspect of the pins, squeezing together a bit. Probably a temporary fix, if at all. I bought that part new less than a year ago for $65, now they are twice that! Part # P4013-12022. Available at above, or here http://*************** I don't know how to check the amp itself. I had a similar experience, worked for a while, then died. Good luck!

[erubin]

Thanks toomany,

I already squeezed all the female ferules so that they fit tight on the pins. I am certain it is either the pickup or the amp that is bad (maybe both). I want to know if the pickup can be tested with the engine running even if I disconnect it from the amp. Will it generate volatge unconnected? BTW I measured 80 ohms between the signal pins from the crank pickup.

[funola]

See post #17 in this thread for a tach diagnostic procedure.

Help troubleshoot an intermittent tach.

If you can't get yours working, send it to me. I can repair it.

[erubin]

Funola,

Thank you. Will do the tests and get back.