I agree with leaving well alone,
But I had a HP10811 which had no EFC control.
I agonised about why this would be and bought a few varicaps,
- I could not find suitable current sources and I had resistors.
When I opened it I found the junction of the varicap diode,
the oscillator capacitor and a resistor was dry. No solder at all!
When it was soldered all worked well. Another unit was inspected and
it had a lousy
joint in the same location. The serial numbers of the two units were
years apart.
Now I am more confident with them I am thinking of trying to reset
the oven temperature
to suit my ambient temperature, the aged crystal and the drift of the
thermistor and resistors.
I may even lag the HP10811 with some insulation to reduce the
internal temperature gradients
and reduce the oven power.
The method would be to use an external resistor which would be set to
several likely values
increasing the temperature past maximum frequency, then the same
values decreasing the temperature.
An hour or so at each temperature. Then a least squares regression to
a parabola which
should show the best value.
cheers, Neville Michie
On 30/03/2010, at 9:49 AM, Mike S wrote:
At 05:59 PM 3/29/2010, WarrenS wrote...
Bert wrote: >"would not feel comfortable tearing into the unit."
I tend to agree, First rule is "do no harm",
I've got this rule that says "If I don't know what the insides look
like when it's working, I won't know what to look for when it
breaks." :-)
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