VDO/Motometer Quartz-Zeit clock repair

[adam quantrill]

I have a Motometer Quartz-Zeit clock in the Wedge (1989) that hasn't worked for a while so I took it out today and opened it up.

It's the type with a second hand, the cog that drives the second hand is driven by a polyphase magnet/solenoid that ticks once a second. Now it's on the bench when I connect up 12V it ticks feebly once a second but doesn't move the hand (not even a small jolt).

In the driver output apart from the solenoid coil there are a couple of electrolytic caps which look like possibly 100uF from what's on the cans. My money at the moment is on one or both of them being duff.

As the quartz oscillator and 23768 divider are working it's making the per-second tick so no need to get the 'scope out to check that.

If anyone has any experience getting these working again let me know. It'll be worth it as they seem to go for £70 + on the flea.

[Rowley-Birkin]

Hi Adam, my friend has just repaired one for another friend and it was the caps that were very weak. replace those and I think you should be alright again.

Jase.

[adam quantrill]

Thanks Jase if you can confirm what value your friend used that would be useful. Presumably 25V breakdown should suffice.

I'll get some top quality ones size permitting.

[Rowley-Birkin]

Ill ask for you.

[Rowley-Birkin]

He thinks they were 1000 Micro farad if that helps?

[sabre]

This may help, the one used in Porsche of the 80s uses 100uf.

[adam quantrill]

Hmmm, a factor of 10...

I think I'll try some 100uF onthe bench and if it works get some long endurance ones.

Also check the voltage swing with a scope in case they are being driven reverse polarity (in which case better to get unpolarised ones), and to check the overall voltages present.

[Wedgehead]

I have to tell you, after reading your entries I almost wish my clock was broken. Very interesting!

[adam quantrill]

You wouldn't be if you had to get it out of the dash!

[Wedgehead]

[adam quantrill]

Just stuck the clock on the scope in the lab, one cap is shorted the other is running at about 5V with a 1V 1Hz square wave superimposed. So at least the caps are running a healthy +ve bias.

The blue trace is the 32kHz crystal. Yes it has a strange amplitude modulation superimposed...



I shall replace the shorted cap first and see what happens. As the other one seems good I can also measure it to double-check the value.

[440Interceptor]

adam quantrill said:

You wouldn't be if you had to get it out of the dash!

Speaking of which, mine's stopped and so has its light, so I assume no power. How do I get it out of the dash Adam?

[adam quantrill]

1. Undo two nuts at the rear//just above the radio aperture.
2. Ease out the wooden fascia CAREFULLY
3. Unscrew metal dash panel (2 self tappers)
4. Pull panel out, to remove the clock.

I think the existing bulb in mine is very weak so I'll be upgrading it before refitting, probably with a LED or 2.

[440Interceptor]

Thanks mate, I shall give it a whirl.