Renault 90-34 tachometer stopped working

[moog]

Hi there,
Tacho has just stopped working on my Renault. I was hoping to see a cable at the rear of the unit but instead it has a connector box with 4 terminals. I’m also unsure where the wires connect to the engine.
Any advice on what I should be checking to find the fault.
Cheers

 

[john432]

Check the fan belt first. I am fairly sure the tachometer gets it's signal from the alternator. Some kind of pulse from the alternator that's interpreted as engine rpm.

 

[moog]

Fan belt is good and all connections to the alternator are tight and clean. Can add a pic if that helps.
Could I do a multimeter test on the connector block to tacho to see if power is coming in? What are the four terminals, and what setting would I be using on the multimeter, ohms?
Cheers

 

[john432]

Just did a bit of Google research! The tachometer takes an AC feed before the rectifier diodes on the alternator . So I guess it's the Hertz of this feed that gives the tachometer reading dependant on engine speed. So the feed from the alternator to the tachometer would probably be only read with the multimeter in the AC voltage setting, and should be undetectable in DC... . I'm afraid that is the limit of my knaulage.... I could phone a friend?

 

[moog]

Can we ask the audience...lol
Thanks John

 

[john432]

Just a quick thought, is the alternator charging properly? Try the voltmeter across the battery, start her up and the alternator should be pushing the voltage up to around 14.4 volts ish.

 

[moog]

Just tested her, putting out 14.44V, so presume working ok.

 

[john432]

Yes the alternator must be good... well our audience is quiet.....and 50-50 is not an option.. All I can suggest is that you ask a Renault tractor expert.. I know of two in Carmarthenshire....Merlin Salisbury in Carmarthen, and Dorian Morgan in Talley ,Llandeilo...both do a lot of work on Renault tractors ,both actually specialists.

 

[s~~t shoveller]

not particular to Renault but normally there is a small wire on the alternator and the small spade or ring can corrode or come loose on the wire.had that a number of times.don't know after that...it can look ok but if you give a pull it might part company

 

[moog]

Ok, thanks guys. I did pull the small wire spade connector off and it seems ok. Just in case, I will give it a waggle while my boy watches the tacho. Good to get him off the iPad!

I did put the multimeter over the connector block on AC. 2 terminals were nil, other was 16hz and final one was 31hz. However, they did not increase when I increased the revs.

If no one else has any suggestions I will follow up on John’s contacts.

Appreciate your help, ta

 

[s~~t shoveller]

Would two of the four wires be the illumination/live when side lights on ?still no help with the tacho though.sorry.

 

[moog]

Thanks, I’ve found one is an earth connection and another is 12v for illumination. I’ll check the other two again, but if the reading does not increase when increasing the revs, I presume the sensor on alternator is defunct. I wonder if that can be replaced separately to the alternator.

 

[john432]

Were you actually reading the hz or actuall ac voltage with your multimeter? My gut feeling is that you were reading an AC voltage of 16 and 31 volts, probably constant as the alternator has a built in voltage regulator . From what I can work out by Google searching, there is nothing special on the alternator to power a tachometer, other than a tapping to one of the output coils before the diodes . It's the AC Hertz change that determines the rpm shown... mains power is 50hz, that's why generators have to run at exactly 1500 or 3000 rpm ( common ones) to achieve that.

 

[moog]

Yes, you right, I think I was measuring AC volts. I’ve tried my second tester which is a better quality Fluke and have different results. Again, I am measuring AC volts, but I get a figure of 10.50 on tick over, but going up to over 10.65 when revved up, then back down to 10.50 on tick over. The other terminal gave a static reading. Not sure how I measure Hz as the tester automatically displays either the DC or AC voltage.

 

[Pennine Ploughing]

they were a paris rhone alternator on most Renault tractors, and the taco clock gets its feed from the single wire opposite the charging wires, brown/white if i remember right, its usually on a ring connector with a8mm spanners size nut,
that is the exciter wire for taco,
the plug into the taco has 4 terminals, 1 for earth a general earth inside, 1 for side light ilumatation or back light, 1 for live feed to hour clock this is a steady live when alternator is charging, and puts an hour on every hour regardsless of revs, and last 1 for exciter to rev counter not sure but think this pulses and the faster the alternator runs the faster it pulses and thus the rev counter goes further up the scale

 

[moog]

Thanks PP, very useful info. I’ve found the wire and cleaned terminal.
I’ve noticed that the revs and hour meter have both stopped working on the tacho so wondering if it’s a problem with the tacho unit itself.
I presume I could test the exciter wire straight off the alternator to confirm it’s working at the source?
After looking up the operators notes for my multimeters, I see I have no hz settings on them, so that’s a bummer.

 

[Pennine Ploughing]

Thanks PP, very useful info. I’ve found the wire and cleaned terminal.
I’ve noticed that the revs and hour meter have both stopped working on the tacho so wondering if it’s a problem with the tacho unit itself.
I presume I could test the exciter wire straight off the alternator to confirm it’s working at the source?
After looking up the operators notes for my multimeters, I see I have no hz settings on them, so that’s a bummer.

It's 25 years since I was a renault fitter, so a bit rusty off memory, but is about as much as I remember

 

[fermec860]

Has anyone got simalar tractor nearby if they have try swaping tachometer over that will tell you if you’rs is at fault

 

[moog]

The neighbour over the hill has the same model but his tacho has stopped as well! He is getting someone to look at his so I will swap them over once his has been repaired. Good plan. Cheers

 

[Hjcarter]

I had a similar problem.

I found a block connector between the engine and cab on my 70-12, gave it a jolly good wiggle and a shove and we were working....

Did you get yours sorted?