[time-nuts] Repair of PRS10 Lamp Assembly
Brucekareen at aol.com
Brucekareen at aol.com
Mon Mar 18 00:24:37 UTC 2013
I am afraid the PRS-10 lamp starting algorithm is a little involved. I
believe that once the lamp temperature is in the starting range, the
microprocessor ramps up the drain and possibly gate voltage of the heating
oscillator FET until the bulb strikes as evidenced by a DC signal at the detector.
If the lamp overheats (as measured by thermistors imbedded in the back of
the lamp block), at some point the microprocessor will reduce the drain
voltage to a safe steady-state value.
The starting constants for each individual PRS-10 are factory-set in the
unit's programmed software, and as far as I know, access to change these
settings has not been made available yet to end users. This makes it
difficult to swap lamps between units.
I have a PRS-10 with a lamp that is just on the edge of starting properly.
Since I cannot change the factory-programmed values, I have tried adding
a shunt resistor to increase the lamp current to the point where it would
reliably start. But, unfortunately, other problems seem to be keeping the
unit from working properly.
The only luck I have had in repairing a non-working PRS-10 with certainty,
was one in a Symmetricom 2500 Time Source that turned out to have a failed
Mini-Circuits VCO on the synthesizer board. Replacing the VCO module
restored proper operation.
Perhaps someday the factory will provide end users with access to what are
now "factory-only" settings.
Bruce, KG6OJI
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