Nico - everything can be, also a cold solder joint. If it is so, the cold solder joint can only be at OPTO1. Look carefully at the 4 solder points on the back of the PCB, if the solder point are good.

BUT - I do not believe, that there is a cold solder joint.

Your problem is mysterious, I never heard of that.

What do the diagnostic LEDs on the board say, especially what does LED1 show, when the minute hand passes through OPTO1? It must go off, when the minute hand passes through. If it goes off, the fault is not on the board, but elsewhere "outside" the board. If it does not go off, the OPTO might be bad (it would be the first time for one of my boards), or the OPTO has bad contact in the socket (take the opto out 2 times and in again) or nethertheless a bad solder joint.

But I suppose, that there is some hardware-misalignment with your minute hand or the minute hand is worn out.

Please see this site:
http://pin-logic.com/tz_clock_fix.htm

Please keep me/us informed, the problem is "interesting".

-Ingo TZ-Clock_fault_Nico.JPG

For this reason, the diagnostic LEDs are there
Do not put in the resistor network the wrong way, the white dot on the resistor network (Pin1) MUST notch with the silkscreened 1 on the board (see instructions on my website)!!!!!!!

-Ingo

PS.:
Here is an excellent write-up, of "How to make Twilight Zone´s clock to work smooth without the "crappy" noise". See in the middle of the site.
http://www.pinballark.com/especial.html

Look on my website, go to TZ-Clock-PCB and then click on the french flag. There are at the end some (bad) fotos, of how the black hour interrupting wheel must be installed.

I googled a bit ... and yes, the cpu can be confused, if the big black hour hand gear
is not installed correctly. Look at the wonderful site of Dr. Ed Cheung and look for the following term "Reassembling the TZ clock gears":
http://www.edcheung.com/album/album08/pinball/tz.htm

-Ingo

I spoke with a really great expert about your problem and he will look at it. So please stay a bit patient, we wil find the problems, that must be somwhere on the CP-Board.

-Ingo

Problem seems to be solved!!!!! - after more than 5 years!!!!!!!!!

A friend of mine in the UK had exactly the same problem.

The problem seems to be caused by a miswired switch in another location in the machine. In the case of my friend it was a miswired switch on the slot machine switch.

This is, what he wrote to me:
"... Just thought I would let you know, that I have now got a fully working clock
To cut a long story short (as I spent hours looking), somebody in the past had soldered the 2 wires on the slot machine switch on the wrong end of the diode swapped them round and the clock is perfect now. ...

I asked him the following:
"... How for hell did you find this fault? It is nearly impossible, to find such a disgusting fault. ..."

Here is his answer:
"... I found it by fluke really, I thought I would just test every playfield switch to see, if they all worked and by pure luck there was still a ball in the slot machine so that switch was on.
As I got to the "lite slot machine switch", I noticed that the right slingshot fired as I pressed the switch? After a quick look underneath at the 3 switches I noticed that the slot machine switch was wired wrong.
I swapped the wire to the correct side of the diode and that cured the slingshot fault and when I started a game and got clock chaos it was fixed

Thanks again for all your help ..."

I must not mention, that finding this fault, took many many weeks and hours of time.

Conclusion: If such a disgusting fault occurs with your clock in clock chaos, check ALL your switches in your machine for miswiring and/or a faulty or reverse connected diode on the switch.

I thought, this is a very important information to share with all of you for same future problems.

Tribute goes to GREAT BRITAIN, thanks my friend!!!!!

PS.:
Here is a photo of the switch (in the photo, it is now wired the correct way)

slot machine switch correct (resized).jpg