[time-nuts] HP10811 losing EFC

[Rick Karlquist]

No one has mentioned the fact that the cathode of the varactor
is connected to an internal 6.8V Zener diode voltage reference.
This is another source of trouble.

Rick Karlquist
N6RK


Bob Camp wrote:
> Hi
>
> I sure would do some quick continuity checks on the EFC line before I
> started swapping varicaps out. A bum solder joint opening up is a lot more
> likely than the varicap going nuts in a fashion that still lets the
> oscillator run.
>
> Bob
>
>
> On Jan 15, 2010, at 7:08 PM, Neville Michie wrote:
>
>> Hi,
>>
>> I have two HP10811 oscillators that do not respond to EFC voltage.
>> The latest to fail had been quite accurately set against a TBOLT,
>> one morning (after being on standby in a HP5328A) it was off frequency
>> and would not shift with EFC but would adjust with the coarse adjust.
>> I have bought in two Phillips varicap diodes, BBY40 and BB149A,
>> but before I did some damage fault finding in the HP10811s  I thought
>> it wise to ask for any advice that was available.
>> While I am playing with them I may try to readjust the temperature
>> setting
>> of the oven to get on top of the turnover. Can anyone point me to that
>> article?
>>
>> cheers, Neville Michie
>>
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>
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