Clock goes hyper when engine running

This is a new one on me - any ideas?

Today when I started my 1979 van after a winters lay up, I noticed an annoying clicking noise and when I looked at the clock I saw the second hand was racing round and the clock was working at hyper speed. When I turn off the engine the clock works as normal. Turn it back on and it goes crazy - the more revs the crazier it goes. The alternator is charging at a steady 14 volts. Anybody seen this before?

 

Time machine

What year was it when you turned the engine off?

 

2135 - a problem with the flux capacitor I'm guessing

 

are you sure its not a delorean

 

Fortunately with a van, you'll never hit 85mph

It is odd. What kind of clock is it - quartz? Has it got a manual adjust? Some - not bus types - have a fast (electronic) adjust, but I can't see how a slight increase in supply voltage could make the thing run faster.

 

It's the original clock - not sure if that quartz or not.

 

There was a tick-tock one (actually a real clock, wound up by a solenoid) and the later quartz one. Does yours let out a loud "clonk" every so often?

 

Time stands still for nobody, especially having fun in a bay !

 

Just call it a rev counter.

 

No Snotty - No loud clonk, just a regular tick-tock.

 

Yeh. I thought that. As a last resort I guess!

 

It suggests that the clock normaly has a stabilized supply that doesn't wander about when the engine is running so ....does the fuel gauge drift about when there is change in RPM.? The voltage stabiliser on the back of the instrument cluster only feeds the fuel gauge as far as I know but I guess anything is possible. Otherwise the clock has its own internal unit...ramble...ramble

 

Hmmm. It's never behaved like this before? The only thing that might be different that I can think of is when I was working in the engine bay earlier this week I disconnected the lead from the top of the alternator to re route it, and I got a spark when the spanner touched earth. Would that muck up anything?

 

No fritt - the fuel gauge is fine.

 

The clock has its own timing reference. Changes in supply voltage aren't going to make it run faster

You effectively shorted the battery out (briefly), but hard to see how that would affect the clock. Do you do anything to the alt with the engine running? Outside chance that if you killed one or more rectifier diodes, the AC ripple on the supply might affect the clock.

 

No. The engine wasn't running. The alternator seems to be charging fine. Is there a way to check if the rectifier isn't working properly?

 

A quick crude check: set your meter to low AC volts and stick it across the battery. It may pick up any ripple from a duff rectifier(s).

 

The clock is probably being affected by noise on the supply. This could be something that either you chamged or disturbed during maintenance (very likely) or an age related failure.

Alternator diode popped (unlikely if the engine wasnt runnung when you slipped with a spanner)

Failing insulation round the coil resulting in fast BIG spikes on the 12 volts.

A problem with a rev counter feed affecting the clock - coupling voltage spikes from coil primary straight into the dash.

A loose wire on the supply to the clock and engine vibration makes it intermittent.

Unfortunately using an AC range on a cheap multimeter will usually just give strange readings even on a good battery as they assume there is no DC present. You need to connect a capacitor (condenser) in series with one of rhe probe leads to make it AC coupled .. Or find a friend with a battery powered oscilloscope or scopemeter.
If you are at Techenders, I will be bringing my Fluke 95 scopemeter.

 

Now there’s a challenge. Who’s going to beat a Fluke 95 scopemeter?

 

Did you fix it? There was mention of a rev counter. If you have one and it shares the same Earth as the clock, I'd check that Earth connection.


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