This manual may contain references to HP or Hewlett-Packard. Please note that Hewlett-. Packard’s former test and measurement, semiconductor products and. Chapter 2 Getting Acquainted with the HP C How to Get the Most Out of the HP C “General Information” section of the Operating Manual has. This page is devoted to the repair of my HPC Network Analyzer. section or page of the HPC Service Manual PDF file) and got these results.

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I did also some CW tests and, as a sample, a 1. During normal operations all the LEDs are on and start flashing when the shutdown circuitry detects a overcurrent, overvoltage or undervoltage condition.

Clicking sounds produced by the attenuator and switch relays could also be heard. Hoping that the other few hundred bypass capacitors of this manua, in the VNA will have been doing fine for the next 10 years or so. It seemed to have a good level and it was variable as it shouldbut frequency was way out and only changed in large steps this could be a hint on the problem, I guessed.

It then became apparent that the problem may be with the PWM controller which for some reason restarted intermittently. So I removed the switching pre-regulator box and opened it in a hope to find the answer there. So it appeared the problem was hp753c in the display circuitry. The problem was intermittent, so the troubleshooting promised to be challenging. There hhp8753c no a specific pattern that would allow to predict as to when this may happen next time.

The Service Manual suggested replacing the switching pre-regulator, which was not an option for me because I did not have a replacement. Display color adjustment I had some info about the colors not being accurate on this unit. That was the breakthrough and I realized that the shutdown manyal was caused not by a overcurrent but by a undervoltage.

That oscillator is a 3. I hope you enjoy it!

8753C Network Analyzer, 30 kHz to 3 GHz

And now this is the same signal after the pretune changes: I got it out of the unit and, as expected, there were no external signs of problems. So I proceeded with some hesitation and hoping for the best Other smaller problem was that the power switch was semi-stuck, wth a gummy touch, making it very hard to power up and down the manuwl.


The controller board before the fix. But with some determination and efforts even a very complex equipment can be repaired. I then tried disconnecting the power from the display and that at first let the power supply to start normally, so my first suspect was the display. Here you have the apparently good check of the YO coil drive: The problem was solved. Every once in a while the C was able to start and work for a period of time and then all of a sudden restarted as was described above.

The bad C6 bypass capacitor was replaced with a new mica red one which can be seen in the center of the picture. Cleaning works I have done also some cosmetic work on the hp875c and have also fixed the gummy power button system.

EB5AGV’s Workbench: HPC repair

When the power switch was activated, the VNA appeared to be starting up but as soon as the CRT display was about to come up it produced a hissing sound and the device shut down and immediately restarted in a continuous loop.

The Test Set basically has a frequency doubler to multiply the source signal frequency by msnual, RF couplers on the two test ports and RF switches msnual swap the ports. Checked the pin 2 again, the voltage was changing erratically. But as it runs on one side, internally to the frame, I needed to remove the display section to access it, so I left that for later work.

But as I had never used an C before, I was not aware that the Channel 1 should be yellow instead of orange You can see from page of the PDF what the different displays should be in a working unit.

EB5AGV’s Workbench: HP-8753C repair

To check my theory, I soldered a new 0. If the overload condition was still present it caused the device to continuously cycle the power. In order to get the proper colors displayed, I got the display module out and looked for the R-G-B gain pots.

I could not believe my eyes. The VNA class of instruments was not wide known to or used by the Ham Radio enthusiasts before recently because of very high cost of that type of equipment. The device has a switching pre-regulator encased in a separate box and the post-regulator removable board with all the secondary linear regulators.


The difference between the two was amplified and steered the PWM to regulate the output voltage of the pre-regulator. That puzzled me hp87753c completely. Thanks to the used equipment market for producing such a nice opportunity to learn. In the picture on the right the post-regulator board can be seen in the middle of the frame by the back panel.

So I run all the tests which were related to it. So when one dies on you it is not a good feeling. And the results were, as you can imagine, bad at least for the first one; the other ones seem to be similar to what the manual says, but with some offsets. The problem was with the device not powering on or restarting unexpectedly. Knowing that the analyzer seemed to run fine with an external reference was a good thing, as it really pinpointed the A3 SOURCE as the real culprit.

I connected a scope with a DC input to the pin 2 and The Service Manual instructs to remove the boards one by one to identify which one may be causing the overload condition, which I did with no success. With two independent display channels available, you can simultaneously measure and view the reflection and transmission characteristics of the device under test in overlay or split-screen format on the crisp color display.

I was stunned – a one penny capacitor took down the multi-K dollar device. I got a gut feeling that the problem may be with the power supply itself. It was a small yellow axial 0. The board has LEDs along the top of the board that indicate power status for each post-regulator channel. Unit as received I got the unit knowing it had several faults, so there was not surprise when I got the first display from it: Then all of a sudden the VNA began cycling the power again even with the display power disconnected.