Calibrating the Tacho on a Yanmar 4JH4E

[Ian_Edwards]

I asked this question back in 2018, and got the answer that you basically adjust a potentiometer.
As per another thread, I now have the taco in bits, whilst I fit a new LCD screen.
The tacho still need calibration, I changed the Alternator and associated belt pulleys, so the Tacho reads high, and has done for the last 2 years.
I now see that you re-calibrate this version of the VDO Tacho using a series of button presses, and I have the .pdf which tell you how to do this.
I've also bought a cheap optical tacho, so I know the rpm of the engine.
However, it is going to prove very difficult to operate the button, which is buried inside the tacho, which is mounted in the cockpit combing with limited access through a cockpit locker, and at the same time as adjusting the rpm and reading the optical tacho, which needs to be pointed at a white mark on the crankshaft pulley.
What would make life much easier is if I could attach a remote momentary switch in parallel, with the button on the PCB.
The Tacho has five 1/4"spade connector, only three of which are used.
I've been looking online for a schematic of the electronic or detailed description of the spade connectors, but I haven't found one as yet.
I'm hoping that the unused connectors will allow a remote switch to be temporarily installed.

Does anyone know what the spare spade terminals are connected to, or have access to a schematic of the electronics in the Tacho.

 

[Skipper_Christoph]

Why not unmount the tachometer, temporaryly elongate the three connected cables and move the taco to a position, where you can watch your optical tachometer and press the buttons at the same time. Afterwards remove the cable elongations and remount your then calibrated tachometer to the original position.

 

[duncan99210]

Set the throttle. Measure the revs using the optical tacho. Reset the tacho to match those revs. Job done. The engine revs won’t change appreciably whilst the throttle is in the same position. Or am I missing something?

 

[Mistroma]

Set the throttle. Measure the revs using the optical tacho. Reset the tacho to match those revs. Job done. The engine revs won’t change appreciably whilst the throttle is in the same position. Or am I missing something?

Yes, that's what I would do and not difficult to repeat once or twice if you do pick up a slight difference. I have the same engine and tacho. It has been dismantled a few times to patch the LCD connection until I can do a proper job. Never needed to re-calibrate but did work out that I could leave the panel out to reach the buttons if ever needed.

 

[Ian_Edwards]

The Tacho comes out of the back of the instrument panel, and it's very difficult to remove the panel, it's protected by perspect screen with cutouts for the key and stop button, the screen is sealed in.
I physically can't see the front of the Tacho counter and simultaneously press the programming button. The access to the rear of the Tacho, is head first into a cockpit locker, which is very awkward.
The Tacho need recalibration because I've installed a new alternator, uprating from 80amp to 140amp and changed the belt and pulleys from a V belt to a flat serpentine belt , this has increased the rpm of the alternator.
I could put a temporary extension cable in, that wouldn't be hard, and I must admit, I hadn't thought of that. It would have the same effect as putting a momentary switch in parallel with the one on the PCB. Unfortunately I can't make that cable up at the moment, spade terminals, crimping tool and spare cable are all on the boat.
As an alternative, I can program the Tacho if I know the diameters of the crankshaft and alternator pulleys, and the number of polls in the Alternator. I don't have access to the boat, so I can't measure the pulleys, but I can try contacting the upgrade kit supplier and seeing if they can provide the info'.

 

[[2574]]

I asked this question back in 2018, and got the answer that you basically adjust a potentiometer.
As per another thread, I now have the taco in bits, whilst I fit a new LCD screen.
The tacho still need calibration, I changed the Alternator and associated belt pulleys, so the Tacho reads high, and has done for the last 2 years.
I now see that you re-calibrate this version of the VDO Tacho using a series of button presses, and I have the .pdf which tell you how to do this.
I've also bought a cheap optical tacho, so I know the rpm of the engine.
However, it is going to prove very difficult to operate the button, which is buried inside the tacho, which is mounted in the cockpit combing with limited access through a cockpit locker, and at the same time as adjusting the rpm and reading the optical tacho, which needs to be pointed at a white mark on the crankshaft pulley.
What would make life much easier is if I could attach a remote momentary switch in parallel, with the button on the PCB.
The Tacho has five 1/4"spade connector, only three of which are used.
I've been looking online for a schematic of the electronic or detailed description of the spade connectors, but I haven't found one as yet.
I'm hoping that the unused connectors will allow a remote switch to be temporarily installed.

Does anyone know what the spare spade terminals are connected to, or have access to a schematic of the electronics in the Tacho.

I’d be very appreciative if you could send me the pdf instruction document on how to recalibrate the Tacho. I’ve just fitted a Balmar alternator so the tacho is misaligned. I’ll PM my email address.

 

[Mistroma]

I’d be very appreciative if you could send me the pdf instruction document on how to recalibrate the Tacho. I’ve just fitted a Balmar alternator so the tacho is misaligned. I’ll PM my email address.

I'm assuming you have the programmable tacho and not the type adjusted with a potentiometer. I haven't checked but think one of these files has the information you need.

VDO Programmable tacho with hour meter
VDO Tacho Adjustment

 

[[2574]]

I'm assuming you have the programmable tacho and not the type adjusted with a potentiometer. I haven't checked but think one of these files has the information you need.

VDO Programmable tacho with hour meter
VDO Tacho Adjustment

Thanks, I’ll check.