280z tach capacitor identification

[Zed Head]

Here's a guy who goes way deep on how to convert an older tach to an electronic style.  He had a comment about a calibration tool that was interesting.

Maybe that slot is a potentiometer used to calibrate the tach (mentioned in this article).  Wouldn't hurt to give it a twist back and forth and see what happens.  Maybe it's corroded and not passing low current well.

The material in this article is way over my head but the guy seems to know what he's talking about.

Edit - I used the Hz measurement function on my multimeter a few years ago to calculate RPM from the coil output using the frequency measurement and math like he shows to see if the tach was right.  Just an aside.  You'll get a different number than his 1800 for our six cylinder engines.  My tach was off by 200 RPM, but I never tried to calibrate it.

http://www.nonlintec.com/

http://www.nonlintec.com/sprite/Sprite_Electronic_Tach.pdf

Edited November 29, 2020 by Zed Head

[Zed Head]

He's a car guy and a consultant and likes to share his knowledge.  Might be worth an email.  Maybe he'll have a solution.

http://www.nonlintec.com/contact.html

[crayZlair]

3 hours ago, heyitsrama said:

There is a slight bent at the end of the shaft that holds the needle, nothing that make its bind on the edges, but im trying to massage it back into place.

On a side note what is this component between the white and black wires? If you put a small flat driver form the bottom you can rotate the silver plate on the topside. 

 

 

 

Edit, it seems like a potentiometer, the far left is the ground, the bottom one is the vcc, and the top right one is the output.

Yep, that's what it is.

[heyitsrama]

@crayZlair I'm scratching my head with this one, i cleaned the potentiometer out a bit and verified that it worked correctly, it appears that this is used to `tune` the tachometer to a signal.

I attempted to test out the tachometer on different settings on the potentiometer, but it does not appear to make a different on the `low` RPM only on the high.

I'm scratching my head on this one, what else can cause the tachometer to behave this way, I'll start looking around for other components, maybe @Zed Head is right in saying that there could be something with the ignition module that is related to this, but if so wouldn't the car run a bit funny? I have a spare e12-80 in my parts collection could be worth testing that out. When I tested the resistance for the tach-wire from the coil i also get the same Ohm rating on the ground of the car, i unplugged the coil harness it looks like the coil is grounded through the e12-80 module.

[heyitsrama]

@Zed Head It was the ignition module, the one I was using was a generic e12-80 replacement, i put a OEM e12-80 that i pulled from the scrap yard a few years ago (good thing i kinda hoard stuff eh?) The tachometer works at low RPM now. Well at least this weekend was not a total loss, making slow progress. 🙂 What scares me is if thise12-80 shits the bed, i hear that some of them can fail, really dont wanna be stranded off the road, esp because i like to drive out into the mountains on occasion.

 

Edited November 30, 2020 by heyitsrama

[Zed Head]

I'm kind of sensitized to that because my tach got all weird when I switched to a GM HEI module.  My solution was a signal conditioner.  Not a super fancy one like in the post I pasted but a simple condenser/capacitor on the coil negative wire.  I don't know what causes the noise but the wire to the condenser wire broke once and the tach went bad again.  I fixed it and it worked.

[Zed Head]

It would still be interesting to talk about how tachs work though.  I learn gooder when there's a problem to solve.

[crayZlair]

31 minutes ago, Zed Head said:

It would still be interesting to talk about how tachs work though.  I learn gooder when there's a problem to solve.

Basic tachometer theory: Digital to analog.

You take a digital signal (RPM, converted to PPS, pulses per second, also known as Hertz). You then convert that to a current to operate a meter movement from zero to full scale. Easy - Peasy. 😄

[Zed Head]

7 minutes ago, crayZlair said:

You take a digital signal (RPM, converted to PPS, pulses per second, also known as Hertz). You then convert that to a current to operate a meter movement from zero to full scale. 

Didn't I already say that, essentially?  It's in the comments about using the DMM to calibrate my tach and my simpleton remarks.  Kind of buried.

Actually, heyitsrama still has that damaged component to worry about.  Whatever it is.  Let's figure that one out.

And, on the capacitor question, he showed a nice shiny blue electrolytic capacitor in one of his pictures.  The side view.

[Zed Head]

2 hours ago, heyitsrama said:

What scares me is if thise12-80 shits the bed, i hear that some of them can fail, really dont wanna be stranded off the road, esp because i like to drive out into the mountains on occasion.

Carry the bad one as a spare.  You'll just have to drive home without a tach.

 

[crayZlair]

13 minutes ago, Zed Head said:

Didn't I already say that, essentially?  It's in the comments about using the DMM to calibrate my tach and my simpleton remarks.  Kind of buried.

 

Sorry, I was being rather facetious, thus my comment "Easy - Peasy 😄"

Still going with the damaged component being a varistor. And, I did notice the new electrolytic cap.

[Captain Obvious]

8 hours ago, heyitsrama said:

the one on the right side of the last image is `Hitachi FA8028-6G2` the one on the middle is `Hitachi FA8030--6H3`

Crap. I was worried about that. I found nothing on the internets for either of those numbers. It could be as simple as a resistor or capacitor array, but I suspect it's not.

The reason I was worried about them is that I don't see any transistors on the board. And I'm sure there are some transistors at play somewhere in the circuit. They aren't driving the tach completely with just resistors and capacitors. Problem is if you can't see the transistors, then they're probably buried inside those packs. One could potentially infer the function by reverse engineering the rest of the circuit and try to figure out what is inside those packages. Glad it won't be me.  LOL.

In any event, it sounds like you're out of the woods and that effort is unnecessary.