Redtruck-VA

Pulled it apart and re-installed everything checking as I rewired it. Found a grounding issue and initially ran separate wires straight from one end to the other. Really thought that would correct the problem. wrong. The signal output is around 5.3 and steady through the rpm range. My meter indicated it was a AC voltage. So the best I can figure is the sensor is bad (used item) or the tach, which is new and works up to 1500 rpm and then loses synch. I followed the ground wires and found a loose screw/connection on the cross member near the negative terminal on the battery. Added a second ground and fixed the loose one. Ordered a universal two wire pickup and should have it in a few days and start the installation over again. Almost hope it is the Tach as I like the ruggedness of the OEM pickup.

j_martin

You can't tell anything with a meter and the engine running. It is a pulse train.

You can hook up a dc meter to the output and you'll find that the state change from 5v to near ground (or vice versa) as you slowly turn the engine so the notch on the damper goes past the sensor. If it works thus, the odds of it failing at speed are close to nil.

Without confirmation that the tach matches the application, or a definitive set of specifications, this is an exercise in futility.

Redtruck-VA

Yep, without proper test equipment I can't diagnose what is actually happening to know the problem. Will experiment a little to find a workable solution.
Thanks,

Redtruck-VA

Success, Removed the OEM pickup and installed a ISSPO magnetic pickup and the tach works great.

Redtruck-VA

One last thing, I want to power the gauge light, But at something about half as bright as full power. What would be an estimate of resistor value should I use?

Thanks,

j_martin

What's the part number of the bulb? You could run the dimmed dash lamp circuit to it.

Redtruck-VA

Jim,
It's an incandescent bulb. I'll need to pull the gauge back out to look at it.
Thanks,

j_martin

If you can put an ammeter (the one in a little multimeter will work fine) in series with the lamp and measure the current drawn at full voltage. That is is what I need to know.

Redtruck-VA

Jim, I can do that, might take a day or two, I'm a little under the weather today.


Thanks,

j_martin

Name's John, or J. An incandescent light bulb changes resistance drastically as the filament heats up. That's why a simple resistance measurement isn't sufficient.

Back when I was cutting my teeth in radio, that principle was used to stabilize a cathode heater temperature in high end short wave radios. It was called a ballast tube. (1955 or so)

Redtruck-VA

My apologies John for getting your name wrong. I worked in electronics during the 60's and can honestly say I remember little of it. One of the radio's I installed at a Naval Station over seas was a TAB 7, it was old even then. Used it as a final amp. It had these hugh what looked like hand blown glass tubes. Beautiful machines that kept the place always toasty.. I'll get the current reading to see what is needed.
Thanks,

j_martin

When I was on the Everglades destroyer tender, an ET1 was baffled by a receiver that was dead. He said he tested all the tubes, and found them all in good shape. I touched each of them, and the local oscillator tube and it's ballast were cold. Ohmed the ballast and it was bad. I was SA at the time, and everybody gave him chit that I showed him up in 2 minutes.

By the time I got off that gig, I was running the communications gang. I had created some service procedures that were very thorough and efficient, producing top work in low hours. We bid normal, ripped them out quick, never hit the beach later than 09:00 on Friday, and got fleet awards for our performance. I wrote up the procedures and BuShips rejected my work for idiotic reasons. I joined thinking I'd be a lifer. Took them a couple of years to talk me out of it.

Redtruck-VA

John, well done.. I started out as a ETR so immediately went to a transmitter site. lol.. Didn't enjoy the work and eventually changed rates to Machinery Repairman. Gave them 21 yrs and then worked as a DoD contractor for the second career. Retired now.