I have E4435B signal gen from ESG series that loses output in certain parts of its output range 250..350MHz, 500..700MHz, etc.
The problem seems to be in the VCO or its PLL loop.?
Its output is supposed to be 500..1000MHz before further multiplication/division but lower part of the range is unstable. As you go down in frequency from 1000MHz to 500MHz, somewhere around 690MHz it becomes noisy and at 680MHz it loses signal altogether.
These siggens sometimes have prescaler U313 1GC1-4210 failure, but here it does not seem the case as it is further down the signal path - after YIG multiplier that converts 0.5-1GHz VCO output into 4-8GHz signal.
This instrument is a patchwork of modules and also has some calibration file integrity issues so I am trying to understand whether this is hardware or configuration problem. At the moment I am looking at low level operation of the PLL loop filter and its phase detector.? I only have block diagram to go with http://www.leobodnar.com/HP35650/E4435B%20A24%20block%20diagram.png
I have noticed that the synthesizer board A24 from ESG signal gen series is very similar to synthesizer board A19 from E4406A spectrum analyser.? Their VCO/PLL loops are almost identical.
A24 from E4435B: http://www.leobodnar.com/HP35650/E4435B%20A24%20SYNTHESIZER%20ASSEMBLY%20top.jpeg
A19 from E4406A: http://www.leobodnar.com/HP35650/E4406A%20A19%20SYNTHESIZER%20ASSEMBLY%20top.jpeg
Assuming that Agilent has been reusing their synthesizer design across many E4xxx class instruments, is there a detailed schematic or CLIP for the synthesizer module in other instruments of the same era?
Thanks
Leo
