Hi Bruce,
Thanks for your reply.
I'm aware that the tantalum capacitor is on of the weak points of the RF
amplifer that excites the lamp. After testing the unit and using the
monitoring software available I found that the problem relies on that
specific part of the circuit. In fact the RF unit was burned like the
tantalum capacitor you are refering. Last year I rebuild that circuit
section interely with high quality components with good temperature
reliability replacing the RF transistor, porcelain capacitors and metal film
resistors. The lamp was heated up as well. The unit worked for about 6
months. Now I found again that the signal strenght received by the photocell
has droped below the acceptable value so there is no more I could do except
to send it back to SRS for lamp replacement...
Regards,
Vasco Soares
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Wednesday, August 13, 2014 3:21 PM
Subject: [time-nuts] PRS10 Lamp Module Needed
Vasco,
As Brooke said it is unlikely there are spare PRS10 lamp modules found
outside the manufacturer. The probable reason is that when the PRS10
units are assembled certain adjustments to the firmware are necessary such
as the starting level and final bias of the FET oscillator transistor. As
far as I know, SRS has not revealed how to access to these factory
settings.
It might be possible to repair your lamp assembly. One point of failure
is the Tantalum capacitor found in the lamp assembly. Another possibility
is that the heater resistor may have changed value or opened. Although it
looks daunting, it is possible to replace the FET power transistor;
however, after replacing the transistor in one unit, I found the
transistor's characteristics were a little different than the original and
the operating parameters were not right. I considered adding some
external resistors to shift the biasing, but finally decided to try
another transistor with somewhat different characteristics. But in this
second try I damaged the board.
If the rubidium bulb assembly is suffering from old age, it might be
possible to improve it with a heat gun as discussed on this listt several
times in the past. The bulb is cemented in place, but it might be
possible to remove and replace it.
Bruce, KG6OJI
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