My guess is the burned choke is in series with the Tantalum capacitor.
This is a very common failure mode for these Tantalum capacitors.
There are a number of things that will cause this failure.
1). power supply ripple too high (Tantalum capacitors do not like ripple).
2). Moisture absorbed by the Tantalum capacitor.
3). Voltage rating of the Tantalum capacitor too close to the supply
voltage. ie a 6 Volt capacitor used on a 5 Volt supply.
The solution is to replace the choke and the Tantalum capacitor.
Replace the capacitor with a higher voltage capacitor.
A lot of high end test equipment is prone to Tantalum failure because
the design engineer used the same Voltage safety margin for the Tantalum
capacitor as would have been used for an aluminum electrolytic.
The Tantalum capacitor requires a higher safety margin because the
Tantalum capacitor will short (as you experienced) by a spike above the
allowed for safety margin. An aluminum electrolytic will absorb the
spike, the Tantalum might short.
You should be able to recover the PRS10.
73
Glenn
WB4UIV
On 6/13/2016 6:32 PM, Skip Withrow wrote:
Hello time-nuts,
Well, broke out a PRS10 that I had put away for a project some time ago and
upon power up found that it had issues. Status indicated low lamp output
and high lamp temperature. Duh! Upon removal of the lamp assembly it
became abundantly clear that the magic smoke had gotten out.
If I recall correctly, seems like there was another PRS10 with corrosion
issues in the same area. My guess is that the heat does not help this
situation. I suspect that I may have a full-on heater, which may have
caused the tantalum cap (and possibly other) failures.
Looks like this may be the weak spot in these oscillators. I'm very
hopeful that a rebuild will bring it back to life.
Thought you would enjoy the pictures though. Two are attached.
Regards,
Skip Withrow
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Amateur Callsign: WB4UIV wb4...@arrl.net AMSAT LM 2178
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of the Amateur that holds the license"
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