Barrus Shire Rev counter Broken

[SandyD]

Hi All,

 

Our rev counter has not been returning to zero when the engine has been turned off (usually left sitting at approx 800 revs) but working fine. Today, half way through a run suddenly went jittery and then worked it its way up as high as it will go and is now stuck there. I'm assuming that the cable has broken - am I right or is it somthing else?

[Tony Brooks]

28 minutes ago, SandyD said:

Hi All,

 

Our rev counter has not been returning to zero when the engine has been turned off (usually left sitting at approx 800 revs) but working fine. Today, half way through a run suddenly went jittery and then worked it its way up as high as it will go and is now stuck there. I'm assuming that the cable has broken - am I right or is it somthing else?

 

1. Before it stuck, and possibly now when the temperature drops a bit, it would drop to zero if you turned the ignition on for a second once the engine has stopped. If you turn the ignition off while the engine is running, you isolate the 12V feed to the rev counter so it stops where it is. This is normal behaviour.

 

2. Check that the W terminal on the alternator is nice and tight, the rev counter counts pulses from the alternator, so a loose terminal can produce false pulses.

 

Ditto the 2V feed form ignition "on" position on the switch to the instrument and also the negative connection at the instrument,

 

If all seem OK, then  you may have a faulty instrument.

[Lily Rose]

 

Mine does that randomly and quite frequently. I discovered years ago that if I give it a bit of a whack with my hand it changes albeit not always correctly. If the 1st whack doesn't fix it the 2nd usually does.

[SandyD]

Thanks both, I have turned the ignition on and it has reset to zero, starting the engine it seems to be working again- I will see what happens on our trip tomorrow!

 

[Mike Todd]

22 minutes ago, Lily Rose said:

 

Mine does that randomly and quite frequently. I discovered years ago that if I give it a bit of a whack with my hand it changes albeit not always correctly. If the 1st whack doesn't fix it the 2nd usually does.

In the days when computers used thermionic valves (might first experience) such treatment was known as 'preventative maintenance'. Best not done when coming to the end of an hour's computation.

 

The underlying logic was codified into a 'facility' in which, at the start of a day, or session, the voltage to the valves was increased (I cannot recall whether a steady state of sudden) The logic was that it was better for a failing device to be replaced before losing computational time (which was precious)

[ditchcrawler]

51 minutes ago, SandyD said:

Thanks both, I have turned the ignition on and it has reset to zero, starting the engine it seems to be working again- I will see what happens on our trip tomorrow!

 

I take it your batteries are charging OK, the "ignition" light doesn't flicker at al and your V belt is in good condition. all of these can effect the alternator output which drives your rev counter