AnsweredAssumed Answered

HP 8753C - Bogus error messages

Question asked by hubertus on May 5, 2014
Latest reply on Jun 12, 2014 by dhamilton
Hi all,
I just finished studying electrical engineering. I am doing ham radio stuff as a hobby, and recently, I bought a HP 8753C network analyser with the 85047A test set. The analyser has options 010 and 006, and I had the unique chance to buy it for a very good price. Self test passes, but there is sometimes a strange behaviour:

When the instrument is turned on, after the hp logo a text is displayed for a very short time. It is too short for me to read, however, I filmed it with my smartphone and the text says: "SELF TEST PASSED". But, interestingly, sometimes it is white, and sometimes it is red. When the red one appeared for the first time, I thought it was an error message :-) but it's not, it just "SELF TEST PASSED" in red. My question: is this behaviour normal? text sometimes red and sometimes white?

Since I was a little bit irritated, I decided to run the internal self tests. The PRESET test is PASSed, and the ALL INT test is also PASSed. As well as test #12 (digital control or something like that) is also PASSed. So one would think the instrument is okay, yes? However, I disconnected the test set completely (front panel connections as well as read panel cable) and then the message "CHECK R INPUT LEVEL" appears. I think this behaviour is also normal.

What I did next was to connect the test set. The test set connectors are left open, and the instrument is turned on again. Then it says "OVERLOAD AT R INPUT, POWER REDUCED" (or similar), which is very strange: there is absolutely no active device connected to the equipment and ports are open. Yesterday, when I first turned on the instrument, the message didn't appear, and I could measure a 1.6 GHz band pass filter without any problems. But today this message appears.

Are there any suggestions, what I can do to find the problem and - hopefully! - fix it? As soon as I saw the error, I disconnected everything and turned power off immediately, since I'm very afraid of damaging the instrument. Would that be possible, even if no active device like a mixer or an amplifier is connected to the analyser or the test set?

Hopefully one can give me some hints. As I already saw, Dr Joel being the designer of many 8753's things, knows a lot :-) and can probably give a hint?

Many many thanks in advance!