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914World.com _ 914World Garage _ RPM gauge, testing

Posted by: jtg Apr 29 2010, 08:25 AM

Does anyone have any techniques for testing the 914 RPM gauge? Mine is dead. I have good 12v and ground at the rear terminals and what appears on a voltmeter (I don't have an oscilloscope) to be a varying voltage on the signal wire. I had the gauge apart for cleaning/painting and might have messed it up. I want to make sure before I take it apart again. What type of signal can I feed into it to test it?

Thanks for any help!

Posted by: Spoke Apr 29 2010, 10:13 AM

When you say RPM gauge, I assume you mean the tachometer?

The signal going to the tach comes from the opening and closing of the points in the distributor. This signal will go between ground (points closed) to a voltage more positive than 12V.

According to the waveforms below, the points can get up to 300V.

BTW,

Attached image(s)

Posted by: jtg Apr 29 2010, 12:01 PM

Thanks for the info. Looks like I need to find another older type vehicle to hook it up to or a tester with this type of output. I was hoping to some kind of resistance test to check its functionality.