HP 8563E repair

[EE4all]

I am working on a 8563e that shows error 334 LO AMPL. The YTO is fine, and I can show signals on the trace, but they appear low, especially in the low band. Checking the LO distribution amplifier calibration,  I can't even adjust the voltage into the specified negative range. Likely a bad amp, or the drive control for it.

[EE4all]

Ok, CLIPs and service manual in hand. I will follow the diagnostic procedures and report back.

[EE4all]

Just to close this off, the YTO was working, but output was far too low for the amp to work properly without throwing errors. I replaced the YTO with a strong one, and the LO error went away.

[Tony_G]

Just out of interest, did you get a YTO from another 8563E (or one that was a spare part) or did you use a different YTO and work it to fit?

I have an 8563E that works fine but just interested in what you did to repair.

TonyG

[EE4all]

I got the YTO from another 8563E that I got for parts. The original YTO was completely dead, and I ordered a replacement refurbished one off of ebay. That is why in my first post I assumed the YTO was ok, as all the errors except the LO AMPL one went away after making the adjustments for the new YTO. I would later figure out that although it worked, the output being under 0 dBm was far too low. A few days later another very old and broken 8563E that I bought showed up, and it had a strong YTO! I was able to use it to fix the first 8563E. The refurbished YTO is going back to California.

[EE4all]

Here is how I was measuring the YTO output power level, as I didn't have an analyzer that would cover such a high frequency. I didn't bother dialing in the offset to the power meter (for the attenuators). There are 40 dB worth there, as that sensor has a maximum input of -20. Setting span to 0, and then measuring it, the highest point was here, with -4 dB.