[time-nuts] Repair of PRS10 Lamp Assembly
lists at rtty.us
Sun Mar 17 20:34:26 EDT 2013
I'd bet that something is keeping the oscillator from putting out enough RF. The circuit is simple enough that the issue is one of a very small number of parts. I'd bet on the FET…..
On Mar 17, 2013, at 8:24 PM, Brucekareen at aol.com wrote:
> 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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