[Heathkit] SB 634 clock

[Donald Spoon]

The usually reliable clock on my SB 634 Station Console has suddenly 
become erratic this week.

I discovered a couple of days ago (Wednesday) that it had lost lock and 
couldn't be reset.  The numerals seemed to be cycling independently and 
randomly on the display.
I pulled the plug, powered up again, and found I could now reset the 
clock with the switches on the back, but it insisted on running "fast" 
and would gain several minutes each hour.
The next day things appeared to return to normal, and I reset it against 
WWV.   It kept good time for a day and a half, then this morning 
(Saturday) i discovered it was running fast again!

It sure acts like it is losing sync with the AC power line, but why?   
The sync circuit is just a half-wave rectifier off the 20 V AC winding 
of the power transformer, with light filtering to create sync pulses for 
pin 23 of the Mostek clock chip.  This is the area that I am 
concentrating upon, since it forms the sync pulses.   The circuit 
consists of a Silicon diode, two resistors and a capacitor.

I haven't had a chance to open it up and measure voltages or look at 
waveforms yet.  That is on the "to-do" list as soon as I return from a 
trip.  I am soliciting any other ideas or thoughts that I might have 
missed, and am curious if anyone has seen this behavior before.  
Thoughts / Ideas are welcome to help focus my repairs.

In the "Far Out" department:  The episodes of the clock going "ape' have 
roughly coincided with the occurrence of the solar flares this week!  I 
have recently been following the daily changes in the ionosphere, and 
have seen some strange occurrences this week in conjunction with the 
four, X-Class solar flares we have had since 14 May.  Today (Sat.) it 
was reported that Earth was "sideswiped" by a Coronal Mass Ejection, and 
I have noted the MUF going down all morning, when it should have been 
going up as the day goes on.... I saw the same pattern on the day the 
clock started acting "weird".   Any opinions on the possibility of a 
relationship between the two??

Cheers,
-Don Spoon-
K0APK