Jan: UTC clock mysteries solved

By Alan Wooller ZL1AUW

This clock update isn’t about the pendulum clock but rather the bright blue 7-segment LEDs, which live above the ICOM IC-7700 HF rig. Up to 9 May 2018 these showed NZ time, standard or daylight-saving depending. But on that date it was decided (not by me) to have it showing UTC.

This had no effect on the performance of the clock but it changed my attitude to it. Because it was to be used for logging rather than just deciding when to put the kettle on I felt it had to be taken more seriously.

The mysterious UTC clock is rack-mounted above the antenna rotator contol box. The wall clock marks local time.
The digital UTC clock is rack-mounted above the antenna rotator contol box. The wall clock (slaved to the master pendulum clock) marks local time.

The performance was poor. It lost about a second a day. Worse I did not know how to make fine adjustments to the setting. All I could do was to advance it one whole minute.

It has four buttons surrounding the display, unmarked. There is no instruction book.

I figured out what three of the buttons did. The fourth button was a mystery. When pushed it changed the display from four digits to three digits and the right-hand digit advanced once a second. I thought maybe it was some sort of alarm setting. ZL1TOF nutted it out. It displayed minutes (but not TENS of minutes) and seconds instead of hours and minutes.

I made some adhesive labels to put next to the buttons showing these functions.

I looked hard at the performance and decided to do something. I took my time. It was Boxing Day before I got around to looking at the back of this clock. It was all open and there was a trimmer. I started adjusting this trimmer. Ye Gods! A minimum smidgeon of an anticlockwise turn changed it from losing a second a day to gaining a second a day. I backed it off half a minimum smidgeon and now it is gaining at 0.47 sec/day. I daren’t touch it again.

I also had a look at the button functions. Now that I knew what the fourth button did I looked at what it did if I
first held down the first button. This is the “hold-down” button to make the second and third buttons do their jobs, namely to do fast forward and slow forward. I found that the combination “hold 1 while pressing and holding 4” caused buttons 2 and 3 to acquire new alternative functions. Zero seconds and freeze the clock (but only while the button is pressed). Now I have labelled these. So the clock can now be adjusted fairly precisely just like the others.

The ICOM IC-7700 has a clock which gains about 0.41 sec/day. So it is nice to have 2 clocks running at about the same speed at the HF operating position. And they can be kept reasonably in step with each other and not cause confusion.