EB5AGV's Workbench: HP-8754A repair

An affordable 4MHz-2.6GHz VNA

HP-8754A

This page is devoted to the repair of my HP-8754A Network Analyzer.

I got it some years ago, from eBay, in unworking condition. But until recently I had no the time nor space to work on it.

I hope you enjoy this page!


Unit as received

Some inner views of the beast.

Top view:

HP-8754A

Bottom view:

HP-8754A

Now inner cover-less:

HP-8754A

This is the unit in repair position on the auxiliary workbench:

HP-8754A

UNDER CONSTRUCTION


Preliminary checks

UNDER CONSTRUCTION


Troubleshooting Z-AXIS

UNDER CONSTRUCTION


Working on TUNING control

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:

HP-8754A

I took out the front panel to get access to it:

HP-8754A

HP-8754A

This is the control, once removed:

HP-8754A

It is a double stacked BOURNS unit:

HP-8754A

As it was so oily, cleaning from the outside with contact cleaner was not enough so, with some hesitation, I decided to dismantle it...

HP-8754A

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:

HP-8754A

And this is the assembly back into the unit:

HP-8754A

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.


Real-world testing

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:

HP-8754A

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:

HP-8754A

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

HP-8754A

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!

HP-8754A


More to come soon... keep tuned!

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