Reparing HP8566B YTO unlock in 2-22 mode only

[tkamiya]

I am working on an HP8566B with an weird YTO unlock issue.  It works fine with no sign of problem if it is set to 0 - 2.5GHz mode.  Problem only happens when it is set to 2 - 22GHz mode.  There are no obvious blown tantalums.  Tried setting to center frequency 12GHz and bandwidth 2GHz down to 100KHz to see if scanning width was the issue.  YTO unlock continues.

Have anyone experienced something like this?  Because it is working 0 - 2.5GHz mode, I have not done detailed voltage test.  Logically thinking, it should not be necessary but I can.

Any opinions, ideas, and solutions are very welcome.

[Runco990]

Have you had a look at this?   I have repaired BOTH my SA's with this problem.

[tkamiya]

Yes, I did.  As far as I can tell, my case is unrelated to Kerry's problem.  In fact, I kind of follow his blog and knew of his experiences.  My back hurts for lifting those heavy units.  I have several here, so actually, I swapped all of those cards with a known working one and saw the problem reproduce. 

Thanks.