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Repair of HP8594E Low Band Mixer?

Question asked by Pete4 on Aug 8, 2011
Latest reply on Aug 9, 2011 by MikeM
Hello,
I got a HP8594E having a defective LowBand mixer (5086-7748).

As I measured the RF input using a Ohm meter I got about 4.2Ohms only so I guess
one of the 3 parts bonded to the RF input jack has a short.

Located very near to the SMA jack there are bonded 2 parts to ground looking like 2 anti-parallel
diodes. Looking farer along the signal path there is another part bonded to ground which looks
defective.

As the mixer outputs a IF Signal which is about 12dB too small (but it mixes) I had nothing
to loose and disconnected all 3 parts. After disconnecting the 3. (single) part the short had gone.

Can somebody tell me what kind of part this shortening part was? Is it the bias resistor
of the two mixer diodes located on the backside of the substrate? If so how many
ohms had it?

For the 2 input parts: Are these protecting diodes? If so which diodes could be
taken for replacement?

Thank you for your answers
regards
Peter  

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