Tachometer/revcounter

[nomadicstar]

Hi hoping some one can enlighten me please, we have a bav 39 2007. Problem with rev counter, ok on start up then normally 5-10 minutes after starting the rev dial goes to max position and stays there, and doesn't record engine hrs. Have checked for loose connections or anything loose.
Any help would be more than appreciated.
Steve

[Nigel]

My first fault-finding step would be to eliminate the feed from the alternator as the culprit. Access to an oscilloscope would be ideal, but failing that you could try feeding from a "wall wart" power pack with an AC output of around 12V.

Some people think I'm crazy to have an oscilloscope on board, but it has paid for itself (about £200) time and time again. I've got a UNI-T UT81B but the ARM based DSO203 types are also good.

[Konan the Bavarian]

I had this occurr on my 2006 b37, and the fault was in the lcd display.
There is a previous post on this forum about how to replace the Lcd display, but I am not the electronic savvy. I had a separate hour meter installed on engine panel, not ideal, but by far the cheaper option to replacing the whole gauge.
Steven
sv Konan

[landes_h]

I agree with Konan. Replacing the hour meter by another one from electronic stores, [ such as Conrad.co.uk ] is the cheaper solution. Volvo charges a ridiculous price for that. And also the question is, why putting this thing in the cockpit console? The only time you need it, when you make an entry in your log book, which usually is on the nav. table. The easiest installation is by the first step above the hatch to the engine room. The good thing is, it's not weather exposed, so that there's no need for some "water proof" version.

[Nigel]

A faulty LCD does not cause the tachometer to read max revs.