After replacing the diode, the YIG still was not functioning. The problem has to be on the inside of the YIG where all that VooDoo RF stuff is taking place.
I bought a new YIG. I put in a ridiculously low "make an offer" on the auction site and to my surprise, the seller agreed. I was not about to pay the crazy prices they are asking for a new YIG. I would have parted out the analyzer first.
Anyway, after installing the newly acquired YIG, that part of the RF section is now working. YAY!
Unfortunately, I'm still not seeing my input signal being displayed. **SIGH**
After more troubleshooting, I determined that I am not getting output from the A13 second converter. There are only two RF inputs to A13. One is from the YIG, which is now working. The other input is a 600Mhz, -5dbm signal. Now, the problem is that the 600Mhz signal going into A13 is way low. Instead of -5dbm, I'm getting about -25.
I tracked the problem down to a faulty RF amp in the 600Mhz section. However, the part is obsolete and not readily available from the usual sources. It's a MSA-0505, HP# 1826-2421. I found some NOS parts on the auction site but they are coming from Israel. Now I'm just waiting for these parts to arrive. Should take no longer than two weeks.
Now I know why I got this dirt cheap from the auction site. This unit is filled with bad boards. LOL I did not mention that when I first received it, it would not power up. I had to fix the power supply first. I am now repairing the third failure. It went from the power supply, to the YIG and now the RF amp. It's fun though.