Smiths Tacho Fault

[Sidon]

Hello all. I have a 1.8TC based Roadster with Pertonix contactless ignition and Lucas sports coil. My tacho stopped working at the weekend. It is a Smiths 12 volt -ve earth unit with connections +ve feed, pulse from coil -ve, and earth (plus instrument lights). It has worked perfectly for the last few years but, after a winter lay up, I started the car and it worked for 5 minutes then packed in. I have checked the wiring to the unit and this seems ok - I have a good earth and +ve feed, the wire that goes to the coil gives a constant low voltage reading on my electrical test meter. Is this correct? Before starting the car I disconnnected the coil HT lead and turned the engine over a few times to get oil circulating. Could this have damaged the tacho? Car runs great but I feel lost without the rev counter. It will be a pig to get out so I hope someone can at least confirm that the unit itself is likely to be the problem before I start taking the dash out. Any help will be much appreciated. Thanks.

[lil_red_roadster]

Re: Smiths Tacho Fault

I experienced something similar several times...Firstly the coil wiring had gone very brittle through the loom, so I stripped most of that away and replaced it..that fixed it the first time. The second time was down to a poor quality glass fuse in the fuse box, where vibration caused the internal fuseable bit to "lose" contact with the end caps...a new fuse cured things...but it took some tracking down. The third time was a "tired" connector on the rear of the tacho. That's not to say rev counters don't fail...but you're right to suspect the wiring first...have you tried running fly leads direct from the ignition switch and +ve coil to the rear of the tacho and running the engine..this should confirm/disprove wiring as the culprit.

[Sidon]

Re: Smiths Tacho Fault

Thanks Jez. Didn't think to try fly leads. Tis a good idea. I can just about get to the connections on the back of the rev counter. Will try this weekend. Fingers crossed it is wiring only - I have a feeling that if I have to take out the dash I will end up with a complete redesign because I have never been entirely happy with my first effort (bit amateurish and too plain).

[b_caswell]

Re: Smiths Tacho Fault

Make sure the rev counter prefix is RVC as those with RVI are not compatible with any electronic ignition system.

[Sidon]

Re: Smiths Tacho Fault

I tried fly leads and checked the earth but no joy. Ben - it is RVI prefix, I think, but it has worked with the Pertronix for the last 3 years without problems. I can't see that the problem can be anything other than the instrument itself. I am thinking of taking off the front bevel, glass and dial (it is much easier to go in from the front than try to take out the dash) to have a little looky inside in the naive belief that I may find a handy loose wire. What do you think?

[Sidon]

Re: Smiths Tacho Fault

Sorry Ben, you were right, it is RVC. I also realised last night that I will have to take out the rev counter to look inside. Hmmmm!

[b_caswell]

Re: Smiths Tacho Fault

If you can get the front bezel and glass off the works are held in by two screws on the back undo those and lift out the dial with all its works. However all the books say its not serviceable. I think that spinning the engine over with the king lead out may have caused the problem as the king lead should have been run to earth to discharge the coil.

[Sidon]

Re: Smiths Tacho Fault

I'm resigned to replacing the rev counter and am watching Flebay. Just a thought though, has anybody in the club got a Smiths RVC 2414 they would like to sell? Thanks.