I received an Agilent N9340B 3Ghz Handheld Spectrum Analyzer with a note that it passes all self-tests but does not respond to input signals. I took the gamble that it’s the RF input connector got disconnected somehow.
I opened up the case and noticed that the 40Mhz cable was unplugged, so I was half-correct. I connected it and got a signal at the precise frequency, but the amplitude doesn’t look quite right. It’s around -20dB off. When I scanned it across the full 3GHz band, I noticed the amplitude roll-off when I scan below 800Mhz, and I got very little signal left when I get to somewhere near 10Mhz.
I tried running a user calibration with a 50Mhz CW source but it failed amplitude calibration. Apparently the unit is not fully working. No self-test errors though.
So I opened up the unit and the RF section. The front side of the board doesn’t have any visible signs or unusual smells, so I suspected the improper gains is caused by the input attenuator HMC307:
I was about to order the chip, but because of the lead time, I decided to just take a picture of everything and analyze it off-line:
After removing the screws holding the N-type terminal so I can get to the back side of the board for taking pictures, I noticed the RF in connector just fell off the board with the pad:
That means the RF in is not touching the board! I resoldered the connection after I put the board and the connectors back to the RF module slab. Once I put unit back together, I turned it on again and everything works perfectly! The power level is flat and within 1dB of what my 8648C pumps out. I did the user amplitude calibration again, it passed, and everything was spot on!
I am extremely impressed that you were actually able to diagnose/ repair it / but, most importantly—>>. You were able get it put back together! I would still have a “extra parts” cup remaining after attempting such a repair. LOL I have the n9340A model and need to replace the dc power in coaxial jack and just didn’t have the guts to proceed once I had the rear case removed. I am also experiencing a problem with the internal battery. i purchased the unit from an eBay seller who had stated the battery was bad and needed replacement. I replaced… Read more »
I had a similar but slightly different problem with a N9344C bought directly from Keysight on eBay: the battery won’t charge within the unit. They gave me a free new power supply and new battery for testing (not included in the purchase) and I confirmed those are not the reasons. They ended replacing the digital logic board (nothing to do with the analog side) and returned it to me calibrated at no cost (calibration was also not included in the purchase) because they have to cal after repair. Seems like there’s a weak spot in their power management (charging, switching… Read more »
Hi, friend. I can see that you have done an excellent job on your N9340. I also have a N9340B, which is out of calibration. All measurements give me readings of about 6 db, below the actual value. I was never able to execute running a user calibration. You can see that you have made it. Could you explain to me how to execute the calibration routine of the N9340?Report
Thanks! Regard!! Beto.Report
You can’t cal this away. There’s a amplitude self-cal under the system menu, where you use a 50Mhz source, but it’ll fail.
I recently had something similar developing and fixed it myself after a lot of research. It’s very difficult board level troubleshooting. I’ll have to charge a repair fee to work on it.Report