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hp8753c loss of power output

Question asked by jack_0 on Feb 1, 2012
Latest reply on Feb 13, 2012 by Dr_joel
Hi
My precious hp8753c has suddenly failed. It comes up with message 'no IF found, check R input level'. It is connected correctly, rf out thru a 3dB split into the R input. Checking power levels on the rf out port shows there is nothing coming out.

Have put together an extension lead for the S3 source unit so it can be run outside the mainframe. The 3.8GHz cavity oscillator power out seems to be ok, ~10dBm. There is however some frequency instability here, approx 5MHz jumps going on, with about 60mV of instability on its supply rail. This in the form of ~1Hz step changes. The supply to this measures about 28.3v across the filtercons fitted to the oscillator barrel.

Measuring the YIG shows no power out. Have unscrewed the YIG from the S3 unit and measured the supply rails on the small pcb attached to the base of the YIG. This shows that the +/-15 and 5v supplies are ok, but the rail marked as -40v is now at +0.9v.

Could it be, perhaps optimistically, that the supplies back inside the S3 unit have failed in some way or rather depressingly, the YIG has failed and is corrupting the supplies. I suppose the YIG could be checked by running it outside the unit on external supplies, though not sure about driving the coil, etc.

Any advice would be greatly appreciated, especially if documentation for the 2x pcb's inside the s3 unit could be had.

best regards
jack  

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