[Heathkit] SB 634 clock

[Paul Kraemer]

Check the connections in the counter decoder chips
Pull the chips that plug in and clean socket and pins with de-oxit and re 
seat the chips
Replace the electrolytic caps
Paul K0UYA
----- Original Message ----- 
From: "Donald Spoon" <drspoon at sbcglobal.net>
To: "Heathkit" <heathkit at mailman.qth.net>
Sent: Saturday, May 18, 2013 12:54 PM
Subject: [Heathkit] SB 634 clock


> 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
>
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