[Test-Equipment] Help needed with a 5350B

[Pete M]

Tried for same help on HP Site and got no replies...is this that rare of a counter that no one knows about it?.

I recently acquired 2 pieces of 5350B's. Both pass self test and pass Diag's, but the dia for IF frequency  in automatic mode shows 0 Mhz (typical of no input?).  A6 Board has yellow light (not Green- if ok) and A5 has flickering (no lock) red LED....(again indication of A12 (U1 sampler) ? ).  But both appear to have the high range (.5-20Ghz) blown or at least the same problems. Low range on both (10Hz-525Mhz) work fine. 

Is there a common failure part?  Is it Repairable and part obtainable? Where should I start to look for the problem (I am trying to save time and not reinvent the wheel)? Is it the sampler in fact the U1 sampler on A12?  I also obtained a 5343a with the same problem.  I have all manuals on CD for both units.

Thanks,
Pete