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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It can be seen in gp8753c above picture along the edge of the right half of the box. The right half was the line input and the controller circuit, which became the subject of my further investigation. 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 I proceeded with some hesitation and hoping for the best The Service Manual suggested replacing the switching pre-regulator, which was not an option for me because I did not have a replacement. But as I had never used an C before, I was not aware that the Channel 1 should be yellow manuzl of orange This was what I experienced one day when my VNA became erratic.

EB5AGV’s Workbench: HP-8753C repair

The controller board before the fix. The problem was solved. I put the assembly over the analyzer, in vertical position so the control cable could be plugged while adjusting it by means of a long plastic trimming tool: 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.

Good example of something being at the wrong place at the wrong time!

The Service Manual instructs to remove the boards one by one to identify which one may manua causing the overload condition, which I did with no success. More to come soon 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. But I stopped early, as it manyal 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.


8753C Network Analyzer, 30 kHz to 3 GHz

After spending time with a pen, paper and a continuity meter to understand the schematics, and search on the Internet for the datasheets of the parts used in the pre-regulator, I got what I wanted which was understanding the power supply PWM controller circuit. 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.

So I removed the switching pre-regulator box and opened it in a hope to find the answer there. In the picture on the right the post-regulator board can be seen in the middle of the frame by the back panel. The construction of the switching power supply is interesting and deserves a larger photo. 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.

So that was a good starting point! The VNA Service Manual did not go to the level of details about the power supply that were needed to repair it.

So, yes, mznual seemed like the VNA was working fine!!! It was a small yellow axial 0. 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.

Also, it was unusual that this type of component, a small axial bypass capacitor, would develop resistance and caused that much of a problem, rendering the whole system unusable.

EB5AGV’s Workbench: HPC repair

The problem was intermittent, so the troubleshooting promised to be challenging. Here you have the previous apparently good check of the YO coil drive, which showed some offset: So I went bed at about 3AM local time Here you have the pots: To do that, I have got out the display assembly, have carefully cleaned it, and then have cleaned and greased the power button mechanism: The device has a switching pre-regulator encased in a separate box and the post-regulator removable board with all the secondary linear regulators.

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I got it out of the unit and, as expected, there were no external signs of problems. Source adjustments As I said before, I was afraid of trying any test which would write on the configuration EEPROM, as I had no way to restore the previous configuration if things got worse The cost of this type of equipment is still high these days and is in the range of several thousand dollars.

This time removing one or two boards in no particular order allowed the power supply to start.

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: There was no other circuits connected to the pin 2 other than the bypass capacitor which I marked on the schematic as C6. This was a manusl challenging but interesting project and a good exercise for the brain. That was the breakthrough and I realized that the shutdown condition was caused not by a overcurrent but hp8573c a undervoltage.

Here you have what I got: I hope you enjoy it! Hoping that the other few hundred bypass capacitors of this type in the VNA will have been manuql fine for the next 10 years or so. I looked at the mechanism and there was lot of old grease on it.

The following part of the schematic shows the critical elements of the PWM controller. The two halves mqnual the box have connections with each other via disconnectable wire cables. I got a gut feeling that the problem may be with the power supply itself. It then became apparent that the problem may be with the PWM controller which for some reason restarted intermittently.

So when one dies on you it is hp8753f a good feeling.