GaAs FET Troubleshooting: Assembly Not Working

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SUMMARY

The forum discussion centers on troubleshooting a malfunctioning assembly of two Gallium Arsenide Field Effect Transistors (GaAs FETs) in a high-frequency (HF) system. Despite correct voltage readings at the drains and sources, the assembly has ceased to function. Participants emphasize the importance of providing a schematic and part numbers for effective diagnosis, suggesting potential issues such as a shorted inductor, open capacitor, or faulty solder joints. The discussion highlights the need for detailed information to avoid guesswork in troubleshooting.

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Ravaner
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Hello. I use 2 GaAs fet in a HF system. This assembly worked properly for several weeks and now doesn't work anymore. Before replacing these 2 transistors I would like to know how it is possible that all voltages ( drains & sources) are still correct, while the complete assembly stopped to work ?
 
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Can you post a schematic? Are they in the output that drives a 50 Ohm load? How much power were you pushing out to the load? Was the load ever disconnected?
 
Last transistor drives 680R and power "extracted" from this stage is probably les than µW. My question is why voltages are still the same as when this assembly was Ok.
 
I think we really need at least a partial schematic and part numbers to help you. Otherwise we would just be guessing.
 
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Well, a shorted inductor or open capacitor come to mind; and of course a faulty solder joint, cable or cable connector.
Just the usual suspects.
 

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