[time-nuts] HP10811 losing EFC
namichie at gmail.com
Sat Jan 16 04:07:09 UTC 2010
Hi, thanks for the constructive comments.
I took both units out of their cases and gave them a visual inspection.
I tested the varicap diode as a diode, and checked the values of
When I re-assembled them one of them now works OK. It will take some
time to see if it is stable.
I have an instrument that I can run them in which has an EFC lead
that I can easily lift,
so I am going to apply about 20V through 1megohm to the EFC terminal
and see how high the voltage measures,
that should give me the 6.8 volts regulated plus a diode drop. The
diode and the capacitor should stand 20V.
I dont like trying to run it while dissasembled, that can lead to
disasters, but this test should show if
the 6.8 volts is a problem. Failing that I will unsolder the varicap
and measure its capacitance on a bridge with changing bias voltage.
Thanks again for the suggestions,
On 16/01/2010, at 11:54 AM, Rick Karlquist wrote:
> 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
> Bob Camp wrote:
>> 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.
>> On Jan 15, 2010, at 7:08 PM, Neville Michie wrote:
>>> 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
>>> and would not shift with EFC but would adjust with the coarse
>>> I have bought in two Phillips varicap diodes, BBY40 and BB149A,
>>> but before I did some damage fault finding in the HP10811s I
>>> it wise to ask for any advice that was available.
>>> While I am playing with them I may try to readjust the temperature
>>> of the oven to get on top of the turnover. Can anyone point me to
>>> cheers, Neville Michie
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