Testing tachometers?

[ianspain]

Hi, Im looking for some advice on testing a tacho. It supposedly worked when i brought the boat, although i dont recall seeing it working, but the needle just sits around the 7000rpm mark now and refuses to move. The warning guages all work on startup. Does anyone know a way to test the tacho before i go to the expense of running it into wynnum marine? Any help would be appreciated
Thanks
Ian

[banshee]

Could be your alternator is fried I know that Mercury tacho's run of the alternator,might be as simple as following the wiring back and checking for bad conections or otherwise finding someone who has a multimetre and delve a bit deeper.

[ianspain]

Thanks Banshee, will trace the wiring back and test it all. i'm ok to dabble but just have no knowledge of tacho's. Cheers
Ian

[rajawolf]

Is it at 7000 without motor running?.....or with motor running..the settings on the back of tacho mybe set wrong. they have a pullout setting pin you have to set to the number of pols on the alternator. (for mercury motors anyway)

[ianspain]

Its at 7000 without the motor running and stays at 7000 while it runs. Didn't want to just "have a go" at fixing it till i asked you guys on here. new to this boating thing and ive been reading the forums here for a few weeks and see theres a wealth of knowledge amongst you all so thought i would ask around before handing a wad of cash over to a professional. Hope to have a look at it this weekend and will bear in mind what you have said
Thanks

[rajawolf]

I think it my be broken... give the glass face a tap and see if you get any movement from the needle at all...maybe just stuck.. when u turn the key on..any movement at all, even if just a flicker?

I would not pay to much to have it looked at...better to just buy a new one, they are easy to install.

[ianspain]

Thanks rajawolf, The needle does move slightly when you tap the glass, so i dont think its stuck. i'm thinking i may have to just get a new one. Annoying as i was assured it worked. my own fault. But a small price to pay to get out in the bay and enjoy it!
Cheers

[littlejim]

maybe not relevant, but what the heck.

whenever my tacho played up it turned out I had leant my elbow on the plug that comes into the back end of the control box. This disconnects the plug with the tacho signal in it. Pushing the plug in firmly fixes the problem for me.
It is positioned just where your elbow goes if you forget and rest your arm on the side of the boat.
have a look at the plug just in case it is something that simple.

[ianspain]

Thanks littlejim, something i havent thought of!..will take a goood look tomorrow.
Cheers

[Whats_a_fish]

as for testing i don't know how without another one but if you take it out a specialist electronic instrument repair servie may be able to get it back in working order. It used to cost about $65 for a calibration.
If it is a standerd type or cheaper then that you will be better of getting a new one.