Rev Counter doesnt work!!

[Richard10002]

In September 2007, I was messing around trying to up the voltage output of my alternator. In the end I connected the sensing wire to the battery bank, rather than to the immediate output from the alternator. Immediately after doing this, my rev counter stopped working.

At the time it was suggested that I unmake, and remake, all the connections, which I didnt do - then health events overtook me.

Engine is a Volvo Penta MD22L

My immediate thoughts are that there must be a few places I can put my meter to try and isolate the location of the fault, or that it is at least upstream or downstream of a particular point.

Any suggestions as to what to set my meter on, (Volts, ohms, Amps), and the various places I can put the red and black prongs to get a reading.

alternator

e.g. I think it is the grey wire that comes out of the back of the alternator which feeds the counter.... so I would put one prong on the grey wire terminal, and the other prong where?, and what would I look for? What does the brown wire do? The grey and brown go off in their own wire casing, before emerging in the loom/s above the starter motor.

wiring loom - the grey and brown are in there somewhere, but might just be passing through, rather than connected to anything.

wiring diagram - I can do a bigger pic if it helps

I could also put the prongs somewhere at the actual counter end.... but where? (havent opened this up yet as it's a big job to get the headlining down).

Assuming I get the right reading at the counter end, I would be able to conclude that the counter has blown. If I get no reading at the counter end, the counter is probably OK, and it is something nearer the alternator. If I get no reading at the alternator end, something is wrong within the alternator. all ???

There might also be some connection points in between the two ends, but where might they be?

Is there likely to be a fuse somewhere in the link?

Any thoughts welcomed.

Richard

 

[PembrokeshirePromise]

Richard,

Far from an expert - but I would start with the simple things

From what I can see of your wiring diagram it looks as if the grey wire is the one going to the rev counter.

So I'd start checking that the grey cable was good to the rev counter - i.e. make up a test lead for my meter - so that I can test connectivity from one end of the grey cable to another (either no resistance on ohms - or if you meter has it a continuity check beep)

If you check the connection from the alternator fitting to the fitting on the gauge you should be able to test the actual connectors on the cable.

Then I presume the gauge must have some sort of earth / -ve connection so I'd check that that was good too.

Then at least you know your wiring is OK. Beyond that - do you have Calder boat electrics- he has a section on testing gauges I think

Good luck
James

 

[gandy]

You should see an AC voltage. As I understand it the "W" output for a rev counter comes straight off one of the windings.

 

[alanabnala]

The W terminal is from one of the three phases in the alternator, it provides a half wave rectified signal and when viewed on a scope you see just the positive elements of a sine wave (so like an upsidedown V).

 

[Richard10002]

[ QUOTE ]
The W terminal is from one of the three phases in the alternator, it provides a half wave rectified signal and when viewed on a scope you see just the positive elements of a sine wave (so like an upsidedown V).

[/ QUOTE ]

I'll just get my scope out then /forums/images/graemlins/laugh.gif

I've only got the usual kind of meter, which gives me a number and sometimes a beep.

 

[alanabnala]

As a voltage it is actually 7V, but you may see this as 5.25V to 5.5V, dependant upon the quality of the meter you are using.

 

[ianat182]

From the photo it looks as if there has been water ingress to the white terminal block(black wires)and needs checking for damp/corrosion. Cleaning all those spade terminals would not be a bad start,and WD40- ing them.
Probably a 'sucking eggs' suggestion

 

[Richard10002]

[ QUOTE ]
From the photo it looks as if there has been water ingress to the white terminal block(black wires)and needs checking for damp/corrosion. Cleaning all those spade terminals would not be a bad start,and WD40- ing them.
Probably a 'sucking eggs' suggestion

[/ QUOTE ]

more of a round tuit situation /forums/images/graemlins/smile.gif

I dont think the grey or brown wires connect to anything in there and, as the engine and related stuff works fine in every other respect, I'm reluctant to pull things off that dont need pulling off.

If it aint broke and all that......

(I know, I know! If it goes tits up on a lee shore )

 

[JonJon]

My rev counter didnt work for a while an FWIW I diconnected the wire to the W terminal on the back of the alternator and found the wires were completely fatigued(broken ) at the crimp. Obviously the vibration had got to it over the years. Recrimped a new connector and away we went.

 

[VicS]

Re: Rev Counter doesn\'t work!!

Looking at the wiring diagram in the owners manual you find that the grey wire is the connection for the tach from terminal W on the alternator via pin 13 in the 16 way connector to to S+ on the tach (by which time it seems to have become grey/black!)
The brown wire runs from B1 via pin 5 on the 16 way connector to connection 5 on the electronic module in the control panel (without digging out a diagram of that unit I'd guess that is the charge warning light connection)

The black wire should run from connection D to connection 31 on the starter solenoid and then on to provide the negative connection to just about everything else and to earth via the earthing relay and ground fuse if that is applicable and to battery negative via an isolating switch. (the alternator presumably has an isolated negative connection)

The heavy red wire is the main positive output, terminal B+, connected to the battery via an isolating switch, other relays, and feeding the control panel via a fuse and pin 1 of the 16 way connector.

I do not know what the other red wire connected to the same terminal as the brown wire is. That looks like something that has been added!

 

[Richard10002]

Re: Rev Counter doesn\'t work!!

[ QUOTE ]
Looking at the wiring diagram in the owners manual you find that the grey wire is the connection for the tach from terminal W on the alternator via pin 13 in the 16 way connector to to S+ on the tach (by which time it seems to have become grey/black!)

The brown wire runs from B1 via pin 5 on the 16 way connector to connection 5 on the electronic module in the control panel (without digging out a diagram of that unit I'd guess that is the charge warning light connection)

[/ QUOTE ]

Vic et al,

Before measuring anything, I've taken the control panel out, and found the following, (which may, or may not, be significant):

pic of whole panel

Close up of some missing, (-ve), and not connected, (Brown 61), wires

The brown wire you can see connected to the back of the PCB on a connector numbered 61, has a connector on its other end which is connected to nothing - you can see it on the left of the pics. I'm not sure if that is deliberate as there is a brown wire in the loom from the engine, which seems to go into the PCB with lots of other wires. I'm pretty sure it comes via pin 5 of the 16 pin connector. Also, the alarm sounds briefly, the engine starts and the warning lights come on and off, so I dont think there is an issue with the brown wire 61.

Of more concern is that there is a protective cap for a wire connector on the -ve terminal going into the PCB, but there is no wire, (and I cant find the other end of it anywhere behind the panel). I am wondering if this could be something to do with the powering of the tacho ..... or could it be to do with powering my failed fuel gauge, or both.

There are 4 connectors on the back of the actual tacho, 2 of which have grey wires, one has a red wire and a red/blue wire, and the other has 2 blacks.

Funnily enough, after a long time without seeing the hours meter, this is now clear and seems to be working, although it is flashing.

So... before going further, are the missing -ve wire, and the not connected brown wire issues, and causing the problem, or not ?

Thanks for the input so far

Richard

 

[oilyrag]

Re: Rev Counter doesn\'t work!!

The brown wire on 61 is not standard and is nothing to do with the tach., it is probably an 'owner-fit' +ve supply to another gauge etc. Similarly the red wire is also non-standerd and prob installed as a power supply to summat else. The 'blanked' -ve is standard, i.e. the panel comes like that as it is spare. The tach connections are the 2 grey, which both run back to the 16 pin connector, and the Red/Blue(s) which are +ve supply.

 

[Gypsy]

Re: Rev Counter doesn\'t work!!

I like Pem...Promise's approach. Buzz out the wires so you know they go where you think they go and there is a good clean low/zero resistance connection.

A bad wire or bad earth is the most likely cause but it could also be a bad o/p of the W cct. If you can measure the 5-7v mentioned on W then wiring is the most likely.

Forget the black 'cap' on the logic block in the control panel, it is there as an insulator to stop shorts with the nearby +12v terminal and wires.

As an outside chance, the Alt may not be the source of the Tach signal. Some Volvos including my D2-55 use a small transducer mounted near the flywheel to provide the Tach pulses. In my case there is a grey and a grey/black wire from the back of the tach (like yours) which go through the wiring loom to the engine and then to the transducer. It could be the grey wire to the alt is not actually in use.

Spare wires in engine looms are quite common. The looms and control panels are made to suit many models with different features and instruments.

 

[Richard10002]

Re: Rev Counter doesn\'t work!!

At the alternator, between the grey wire, which we believe is W and feeds the tacho, and the alternator negative wire, (the thick black wire),

I am getting 16V AC and 7V DC, according to my meter.

Are they OK readings? not sure why the difference. Also it was suggested above that I should be getting 7V, (maybe 5V), AC?

Does this help anyone to help me?

Cheers

Richard

 

[Richard10002]

Re: Rev Counter doesn\'t work!!

At the tacho end:

This is a black 4 pin connector which plugs directly into the back of the tacho - presumably feeding the revs and the hours run.

Between the bottom right black wire, (which is just a negative), and the top left grey wire, I get the same readings as at the alternator - 16Volts AC and 7 Volts DC, which suggests that this grey wire is the tacho feed from the alternator, and that it is continuous.

Withe the engine off, the resistance across the black and grey wires is about 0.5 ohms, and the resistance between the terminals they plug into is about 2 ohms, so there seems to be continuity everywhere.

My uneducated guess is that the counter is duff, (I checked, it read zero with the engine running)

If so, where can I get one of these? or a whole new panel?

Thanks again

Richard

 

[Ruffles]

Re: Rev Counter doesn\'t work!!

Before you buy a new tacho (you'll pay through the nose 'cos though it's made by VDO you can only get them from Volvo) get yourself a multimeter with a frequency measurement facility. You should get a clear reading across the tacho. connection.

 

[Richard10002]

Re: Rev Counter doesn\'t work!!

[ QUOTE ]
Before you buy a new tacho (you'll pay through the nose 'cos though it's made by VDO you can only get them from Volvo) get yourself a multimeter with a frequency measurement facility. You should get a clear reading across the tacho. connection.

[/ QUOTE ]

That's easy for you to say!

If I can get hold of one here in Malta, for reasonable money, would I see the actual engine revs e.g. at tickover, about 900 revs?

Given that a couple of people have said that I should see 5v - 7v AC at the W terminal at the alternator, and at the tacho end, the fact that I am seeing 16v AC is making me wonder if there is something wrong at the sending end, (i.e. the alternator).

Any thoughts?

Richard

 

[Gypsy]

Re: Rev Counter doesn\'t work!!

It sure looks like you have good connection from the tach W stud to the Alt.

The reason you get different readings on AC and DC ranges is because the voltage is not truly AC nor DC. As a previous poster said, it is a series of pulses. DVMs repond to these differently than mechanical meters and each DVM is different because of the way they process the signals internally. However the fact you have something at the Tach when the engine is running is a good start.

I have not measured the W point but I seem to recall it is an output of one of the windings before the internal rectifiers or it may be after a single diode.

So this brings us to another of the questions, what frequency. It will be the freq of the pulses produced by the Alt, not the specific motor revs because the Alt is driven by a smaller pulley than the crankshaft so could be 1.5-2x the motor speed. But that is taken into account by the tach design and there is usually a way of selecting an appropriate ration in the Tach to give you true readings...it should be set correctly from the past so you can ignore that for the moment.

Some DVMs do have frequency measurement capability. Whislt we can't be specific about the frequency considering we don't know the pully sizes or even if W gives 1 pulse per alt rev or 3, what you should see is a frequency reading which varies as the motor revs vary.

Is the Alternator charging correctly? If so I doubt the W output can be bad but we are flying blind here.

Now let me ask the real basics. Have you checked the +12v into the tach (measure Blu to Blk) and have you inplugged the tach and checked the connection pins for salt etc?

Finally Richard, since you now have an SWR meter it is time you got a scope and a frequency meter. Frankly I don't know how you sailed this far without them!
Ray

 

[Richard10002]

Re: Rev Counter doesn\'t work!!

[ QUOTE ]
It sure looks like you have good connection from the tach W stud to the Alt.

[/ QUOTE ]

which leads me to think the tacho is duff


[ QUOTE ]
The reason you get different readings on AC and DC ranges is because the voltage is not truly AC nor DC

[/ QUOTE ]

The DC reading was perhaps a misnomer - I took it 'cause I could and, perhaps, it is a coincidence that it reads 7v DC, which is what was expected from the AC reading.

My concern is that the AC reading is 16V AC, rather than the 5V-7V suggested - i.e. more than double?

[ QUOTE ]
However the fact you have something at the Tach when the engine is running is a good start.

[/ QUOTE ]

That's kind of what I thought at first, but as it suggests that the tacho may be duff, it's not so good. If I had found output at the alternator, but no input at the tacho, it would likely be as simple as a connection between the two /forums/images/graemlins/frown.gif


[ QUOTE ]
Is the Alternator charging correctly? If so I doubt the W output can be bad but we are flying blind here.

[/ QUOTE ]

Alternator charges fine at its' usual 13.6V +/- /forums/images/graemlins/frown.gif

[ QUOTE ]
Now let me ask the real basics. Have you checked the +12v into the tach (measure Blu to Blk) and have you inplugged the tach and checked the connection pins for salt etc?

[/ QUOTE ]

13.8V across the black and the blue, (they are actually blue/red, but it doesnt matter). Also 13.8V anywhere else there is a power connection to the panel.

Pins look OK... plugged and unplugged it several times, and sprayed with WD40, (everywhere on the panel including the 16pin connector, male and female). Also checked resistance across the pins as mentioned above, and got readings around 0.5 ohms and 2 Ohms, which suggest some continuity, (I believe).



[/ QUOTE ]

Logic tells me the tacho is duff, but I'd be delighted to find a reason to believe it's not.

Is there something I could feed it with to check? - some kind of supply that I might have on board? - I'm sure I could make a lead up to connect. Or is there such a thing as a rev counter tester?

Thanks for the input - I'm trying to find a replacement tacho or complete panel via the MOA forum.

Cheers

Richard

 

[Gypsy]

Re: Rev Counter doesn\'t work!!

It does point to the tacho but there is still the possibility that the pulses from W are bad. That is why a previous poster suggested looking with a scope. Maybe PM AlanAB to find out what he measured the 5-7v with. As others have said, W is off one of the windings so if the Alt is otherwise working there is not much to cause a problem....but I'm not convinced that it is straight from the winding, there may be a diode in series in order to half-wave rectify it to make +ve pulses. If the diode was shorted, quite possible if the wiring was disturbed, then the AC ready could be high.

I can think of 2 other steps. Hunt around the yard/marina for another boat with the same/similar vintage Volvo panel and ask if you can try your tacho plugged into their panel.

Take the Alt to a motor electrical specialist for checking. Unfortunately they may not pay much attention to the W output for normal tests so you will need to describe your problem and try to filter from the answer whether the technician can really help.