[Heathkit] SB 634 clock

[Donald Spoon]

-Good thoughts on the ICs... I will check them as soon as I can open it 
up.   Tnx!
-Don't worry about the manual... I have a digital copy here plus some 
"updates" I have collected.  Nothing in either addresses this particular 
behavior.
-I am leaving on a 2-week driving trip tomorrow morning, and all my 
attention is focused on getting packed, etc.  I plan on getting into the 
SB 634 when I get back.
-I was just "stirring the pot" a bit with the bit about Solar Flares.... 
I doubt seriously it would have caused this.  Other things should have 
shown some effects too, and they didn't.

Cheers.
-Don Spoon-
K0APK



On 5/18/2013 5:22 PM, Chuck Penson wrote:
> Funny you should mention the SB-634. Just picked one up at Dayton. Dead, but appears to be fixable.
>
> While solar flares are a distinct possibility, I would try pulling and reseating the main clock chip. Over time the pins/sockets can oxidize and become flaky.
>
> Do you have the book? If not I can check my copy for possible solutions. Am currently at Dayton but will be home on the 28th.
>
> Good luck!
>
> Chuck / WA7ZZE
>
>
>
> On May 18, 2013, at 1:54 PM, Donald Spoon <drspoon at sbcglobal.net> 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
>>
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