Test bench tachometer

[SvenVerheesen]

Hello everybody,

I have a 1990 Four Winns 180 with an OMC V6 4.3l engine.

I am upgrading/repairing the electrical wiring within the boat. All gauges are working again except the tachometer. I noticed that when the ignition is switched on that the needle will go to 0. This is an indication to me that there is still something working in the meter. But no output when the engine is running. I do not have equipment to measure whether there is a signal from the "-" side of the ignition coil so i want to bench test if the tachometer still works. Does anyone know how the signal have to look like that the tachometer needs? Or how i can bench test the tachometer?

Thank you in advance!

Sven Verheesen

 

[Scott Danforth]

welcome aboard

remove the grey wire from the back of the tach..... run a new wire from the back of the tach to the coil negative

if it doesnt run then, you need a new tach.

 

[SvenVerheesen]

Hi Scott,

There is a new wire and i have measured with a multi-meter and the connection is good.
Is there a way to repair the tachometer? It is a Kysor/Medallion meter.
My goal is to keep the boat so original as possible so i don't want to change the look of the gauges.

 

[sam am I]

Is there a way to repair the tachometer?

Maybe.......Can you open it up? Take decent pictures? Use a multi-meter? Solder?

But first, make double extra sure it is in fact the tach that is bad

 

[sam am I]

so i want to bench test if the tachometer still works. Does anyone know how the signal have to look like that the tachometer needs? Or how i can bench test the tachometer?Sven Verheesen

https://forums.iboats.com/forum/boa...-audio-and-trolling-motors/10284696-tach-test

 

[SvenVerheesen]

Maybe.......Can you open it up? Take decent pictures? Use a multi-meter? Solder?

I have opened it up but haven't taken pictures yet. I will upload them as soon as i can. I have measured the components and connections on the PCB that is inside. As far as i can measure al resistors, diodes and connections are all right. There is also a DIP chip CS 189 inside. I think it still works because it still zeroes out.

 

[Scott Danforth]

you can send gauges into places that restore speedometers and tachs. however that will cost you more than buying all new gauges.

 

[sam am I]

I have opened it up but haven't taken pictures yet. I will upload them as soon as i can. I have measured the components and connections on the PCB that is inside. As far as i can measure al resistors, diodes and connections are all right. There is also a DIP chip CS 189 inside. I think it still works because it still zeroes out.

Could be cracked trace, bad solder joint, hard to say but, if you have tad bit of extra time and don't just want to throw money at it right out of the shoot, might be fixable, pretty easy to check a few things, and might learn something.

I'll assume at this point an air core meter movement, If so, there's two coils (see below ) you can also check, typically should be around 200 ohms each across each coil. But, by all indications the "return to zero" indicates they are both good.

https://en.wikipedia.org/wiki/Air_core_gauge

Again, the "return to zero" indication is positive sign of, power is on board and getting to the IC, a functional meter movement and at some level, a functioning driver IC.

You've double, triple check input signal is ok? Also, taken the tach, bench powered it and drove it with a separate confirmed signal source?

There is also a DIP chip CS 189 inside. I think it still works because it still zeroes out.

Maybe CS8190?

https://www.onsemi.com/pub/Collateral/CS8190-D.PDF

 

[gm280]

I do remember back in the days I built a Heathkit tach and used a typical 60 herz wall outlet to calibrate it. I mean it is a pulsating waveform and the tach is a simple rectifier that converts the pulse voltage into DC and applies it to the meter. JMHO

 

[SvenVerheesen]

You've double, triple check input signal is ok? Also, taken the tach, bench powered it and drove it with a separate confirmed signal source?

I have tested it hooked up and created a "pulse" with fast tapping the input of the tacho at the 12V supply. It moves so im guessing there is something strange with the ignition coil because continuity from engine to tacho is ok. They updated the engine with a "tune up kit" but i'm not sure what this means. Engine is running allright though.

I dont have a mosfet around so i can't bench test it yet.

 

[Scott Danforth]

how are you verifying continuity on the grey wire? that wire goes thru 3-4 connections between the coil and the gauge.

you cant pulse the +12v supply, you pulse the signal wire to ground.

 

[Alumarine]

Is it possible for you to borrow a 4 stroke tach that you can mount in place of the old one to verify the wiring?

 

[gm280]

Depending on how sensitive your tach is, some tachs will respond with the input tach wire wrapped around a spark plug wire for a pulse. JAT

 

[SvenVerheesen]

how are you verifying continuity on the grey wire? that wire goes thru 3-4 connections between the coil and the gauge.

I have verified this by using a multimeter. Connected one lead to the minus pin of the ignition coil and the other lead to the sense pin of the tachometer. The resistance within this connection was 0,5 ohm.

 

[SvenVerheesen]

Is it possible for you to borrow a 4 stroke tach that you can mount in place of the old one to verify the wiring?

I will search for something like that but at the moment i don't have one

 

[SvenVerheesen]

If the weather lets me i will bring the boat out today and try to connect the tachometer directly at the engine without the connectors and see what it does.

 

[Scott Danforth]

I have verified this by using a multimeter. Connected one lead to the minus pin of the ignition coil and the other lead to the sense pin of the tachometer. The resistance within this connection was 0,5 ohm.

but did you see if it was also worn thru the insulation and grounded anywhere? that would not show up in a simple ohm test

as I stated, run a separate wire to check to see if it is simply the harness path.

 

[SvenVerheesen]

I have tested the tacho yesterday and.. it works!
I first connected it directly at the engine. The tacho worked at that moment.

Next i connected the tacho in the dash and it worked also.
I think at the first try there was bad connection somewhere but i cant trace it anymore.

I also did some soldering on the PCB at the point where the bolts are mounted in the PCB. Also i maked sure the selector switch was making a good contact.

thanks everyone!!

 

[gm280]

I have tested the tacho yesterday and.. it works!
I first connected it directly at the engine. The tacho worked at that moment.

Next i connected the tacho in the dash and it worked also.
I think at the first try there was bad connection somewhere but i cant trace it anymore.

I also did some soldering on the PCB at the point where the bolts are mounted in the PCB. Also i maked sure the selector switch was making a good contact.

thanks everyone!!

When something was working fine and all of a sudden stops, it usually points to an iffy connection that either loosened up, or corroded. That has to be the very first thing to look for... JMHO

 

[SvenVerheesen]

When something was working fine and all of a sudden stops, it usually points to an iffy connection that either loosened up, or corroded. That has to be the very first thing to look for... JMHO

It never worked before the time i had the boat so the problem could be anywhere..