SEE SOLUTION AT THE END....
You may recall my little project of bringing an in-pieces HP 8902A with rear input back from the brink of death. It had been mid stream in being retrofitted from rear to front, then left disassembled. The kit got lost (I wasn't working here at the time).
I managed to scrounge various components, including buying some semi-rigid coax to substitute for the 'plumbing' going to the front connector, fabricating a washer from a piece of hose (for the Audio out connector on the front), etc.. I also bought a new main attenuator (had a known bad one).
I just finished what I hoped were the last repairs and put in a simple 0 dBm 50 MHz CW (no mod) signal in from an 8657B generator. Frequency read fine, RF power reads fine. I had done the RF power and AM/FM self cals and they looked fine. But when I went to tuned RF, I get an ERROR 07. This appears to be a display overdriven error. I went to AM and FM and get errors. When I reduced the power to -10 dBm or so, I get a normal reading.
Any ideas or thoughts?
SOLUTION: This was just a test (that's right, a test).... Remembering this was a mostly torn apart unit, I presumed possible faulty re-installation of things. Another troubleshooting point (before I give away the solution) is that when I lowered RF level to ~-40 dBm, in tuned RF, it strangely let me to the 0 dBm cal. And it thought it was seeing 0 dBm (at actual 0 dBm in, RF power was fine, but tuned RF was off by about 40 dB). This led me to think there was something hokey about how the 40 dB amp stages were kicking in, or their associated logic.
So I started a cable inspection against our working unit - verified correct cabling and properly tightened. I came to a control ribbon cable and noticed the color code position was different between the two units. Voila, a ribbon cable was on backwards. DUH!!
I'm just glad nothing got burned up by the backward cable. I've been running it through it's various modes and looking for reasonable and stable looking readings. Then I'll compare to the good one before sending it out for accredited cal.
That was a Troubleshooting 101 problem if anything was. The good news is that I now have two working systems. Just that much lower possibility of having to buy a new system any time soon.
It's funny you mention this..I just finished calibrating our PATEC 8902A yesterday..just love doing the Opt 50 calibration..great way to kill an afternoon.
Glad you got your problem solved,
Have a great one
Mike