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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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.

EB5AGV’s Workbench: HP-8753C repair

To do that, I have got out the display assembly, have carefully cleaned it, and then have cleaned and greased the power button mechanism: Thanks to the used equipment market for producing such a nice opportunity to learn. The Test Set basically has a frequency doubler to multiply the source signal frequency by 2, RF couplers on the two test ports and RF switches to swap the ports.

When combined with a test set, it provides a complete solution for characterizing linear behaviour of either active or passive networks, devices, or components from kHz to 6 GHz. But before doing them, I thought that a good way to know if the rest of the system was OK, was to check the unit with an external reference. The controller board before the fix. 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.

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. So when one dies on you it is not a good feeling.

Doing some extra checkings This kind of microprocessor controlled systems, even being 20 years old inhave usually a large quantity of self checks which save a lot of time measuring here and there.


I got a gut feeling that the problem may be with the power supply itself. The following part of the schematic shows the critical elements of the PWM controller. It was complete inside I had no way to know before getting the unit, so that was a very welcomed thing and some parts were obviously working, as power supply, fan, CPU, keyboard, display and so on. The bad C6 capacitor is the yellow one in the middle of the picture to the left of the controller IC pin 2.

Hoping that the other few hundred bypass capacitors of this type in the VNA will have been doing fine for the next 10 years or so. As you can see, I was right about the offset being an anomaly. It can be seen from the schematic that this voltage is supposed to be stable and present on the pin 2 all of the time as long as the VNA power switch is turned on. This was a very challenging but interesting project and a good exercise for the brain. 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 unit.

That was the breakthrough and I realized that the shutdown condition was caused not by a overcurrent but by a undervoltage. I did also some CW tests and, as a sample, a 1. Basically, the unit was mechanically sound, except for the missing display buttons cover an spare is already on its way: There was no a specific pattern that would allow to predict as to when this may happen next time.

It can be seen in the above picture along the edge of the right half of the box.

In the picture on the right the post-regulator board can be seen in the middle of the frame by the back panel. I had no choice other than manul download the Service Manual and deal with the problem.

EB5AGV’s Workbench: HPC repair

You can see from page of the PDF what the different displays should be in a working unit. Good example of something being at the wrong place at the wrong time! But I stopped early, as it suggested to do a recalibration and I was afraid that would only make things worse; I checked the RF OUT in CW mode with an spectrum analyzer and an oscilloscope, at different frequencies.


That puzzled me off completely. The display looks really nice, which is manula plus for a 20 year old instrument Locating the faulty assembly I got the CPU board out of the unit, trying to locate a jumper which is named in the Service Manualbut no joy.

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.

But with some determination and efforts manial a very complex equipment can be repaired. The problem was with the device not powering on or restarting unexpectedly. So I went bed at about 3AM local time The difference between the two was amplified and steered the PWM to regulate the output voltage of the pre-regulator.

I got it out of the unit and, as expected, there were no hp8753 signs of problems. I connected a scope with hp875c DC input to the pin 2 and To check my theory, I soldered a new 0. The problem was intermittent, so the troubleshooting promised to be challenging.

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.

Unit as kanual I got the unit knowing it had several faults, so there was not surprise when I got the first display from it: The Hewlett-Packard C Vector Network Analyzer is a massive literally instrument for measuring complex reflection and transmission parameters of the device under test DUT circuits. Next step is to add an external storage unit to the VNA.

Here you have the apparently good check of the YO coil drive: