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Some inner views of the beast.
Now inner cover-less:
This is the unit in repair position on the auxiliary workbench:
After some work, I found that the main source of the frequency unstability was due to a faulty TUNING control. Once I saw it I guessed why: it was full of oil!
This is the unit on its place:
I took out the front panel to get access to it:
This is the control, once removed:
It is a double stacked BOURNS unit:
As it was so oily, cleaning from the outside with contact cleaner was not enough so, with some hesitation, I decided to dismantle it...
I carefully cleaned the helicoidal resistor track and every part. It was really messy with oil.
This is the rotary assembly which hold the cursor. Unfortunately, I broke one of them (it was the first time I opened this kind of unit and I was not aware of the construction; hope this helps other people to prevent that!)
This is the unit which is unbroken:
And this is the assembly back into the unit:
Once back into the unit, even if it is not yet perfect, stability is lots better.
As one cursor was broken, I have lost the FINE tuning control... I hope to find a replacement unit.
As unit is working reasonably well and I want to do some real work with it, which in turn will be useful to get used to this system and to find any other remaining glitch, and until I find a suitable FINE TUNING control replacement, I have placed the unit back to the main workbench (but this time as a test aid, not a patient :-))
This is a general view of my setup:
And these are the views of the different units.
This is the HP-8754A NETWORK ANALYZER on top of the HP-8748A S-PARAMETER TEST SET:
A more detailed view of the 8748A
HINT: this unit uses the fancy APC-7 connectors. If you don't have cabling and gear with them (mostly common situation), grab some APC-7 to N converters
And a very useful accessory, the HP-8750A STORAGE NORMALIZER
HINT: be sure to get the corresponding cable and interface board if you buy one of these!