Oscillator Failure Over Temperature

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dolgaleb

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I inherited an old oscillator design that fails the output power requirement at hot temperature. The system consists of the oscillator stage followed by an AM modulator and last a power amplifier.

The design is comprised of discrete components, no ICs. We have been able to find the zone most sensitive to hot temperatures. But now we need to pinpoint it to the component(s) that are causing the failures.

We already verified the DC power is stable. We applied heat using a heat gun in various areas of the system and found that the circuitry around the oscillator is very sensitive to hot temperatures.

We also, checked datasheets of these components but couldn’t find anything that would justify the problem.

Can you provide a method for finding the actual component causing the failure?
 

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was this EVER stable over temperature? Do you suspect that a component has changed its temperature coefficient?
 

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Seems to me that you would like to know the lineup power amplitudes at each stage, for this. Could be one bad, could be many "just a bit weak" all stacked up. Pout could be depressed by any. How's your small signal RF probing?

Might also look at the problem along calendar lines, like does "yield cliff" appear just after some BOM change or some "non critical" vendor / part (mfr, grade, etc) change trailing by your inventory clearing
cycle.

A hot air desoldering tool or just a soldering iron tip, might give you more localized sensitivity info. But keep the possibility of gang related activity in mind.
 

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But now we need to pinpoint it to the component(s) that are causing the failures.
(...)
We applied heat using a heat gun in various areas of the system and found that the circuitry around the oscillator is very sensitive to hot temperatures.
Click to expand...

How about reporting the failure mode? Silent output? Noisy output? Loss of tuning at the receiver stage?
 

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