[Heathkit] SB 634 clock - Follow-up

[Donald Spoon]

To all those that responded to my original post (repeated below)... 
Thank You!

Just to follow-up.... I returned from my vacation and applied power to 
my Ham Shack and VOILA!  The SB-634 had apparently "cured" itself  
without any intervention on my part!  I have been running the clock 
since mid-June and it hasn't been off by more than a second or two 
since!!  Go figure...

Since it is now asymptomatic, I am quite reluctant to "fix" it... I 
still don't know what went wrong originally, but I think some 
watchful-waiting is in order.  Be assured, I have all of your 
suggestions queued up and ready to go!

Cheers,
-Don Spoon-
K0APK


On 5/18/2013 12:54 PM, Donald Spoon wrote:
> 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
>