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8594E service questions - help me please!

Question asked by jeffx on Nov 10, 2012
Latest reply on Feb 7, 2013 by stu_mm
I am servicing my 8594E /010  analyzer.  It failed at power-up. Was working fine, then suddenly failed.

Have LO UNLVL and FREQ UNCAL warning all the time.  Ran diagnostics.  All PASS except FM COIL DRIVE (page 243).  Ramp does not show - just flat line.  Value changes above 10 MHz SPAN.  Here is what I understand so far:

a) this is a 1st LO failure, which is a YTO.
b) A7 card should generate a tuning ramp - does not work.
c) Page 243 of service manual suggests running unlocked by disconnecting A25 counterlock assy.  Did not correct so A25 is good.

So, I guess A7 card could be bad, or YTO could be bad.  Or LODA could be bad, and A7 is getting no signal to discriminate?

Would appreciate advice on how to sleuth-out problem. I do have another 8594E I can borrow to look at signals - maybe even swap-out A7 card which is pretty easy.  Removing RF section seems hard.