Rohde & Schwarz FSEA 20/30 - Page 1
Forum section: electronics / repair

author: JonH88
author_rank: Newbie
timestamp: August 02, 2021, 12:41:17 pm
content: I will shortly be receiving a Rohde & Schwarz Spectrum Analyser, FSEA 20/30. It fails self test with an error message:STEST aborted: RF-Modul RF-Converter, state 18Any clues to what the source of the problem is likely to be?

author: kendor
author_rank: Newbie
timestamp: August 30, 2021, 08:27:20 pm
content: HiDid you do any progress?I have just received an FSEA as well. Mine fails with "RF-Modul, RF-Converter" faeiled as well (18/0 MUX 12.0: 0.038V, limits: 0.1...6.00V).So far I have opened the device and connected an RF generator at the input. I then measured the output of the input attenuator (at X3) using my other spectrum analyzer. I stepped manually through the RF attenuation and found that the steps are far off from 10dB (you hear the attenuator switching though). I also checked the reference signal (120MHz which is available at X2 coming from X146 from the frac gen during self-test) and this seems to be ok.When I bypass the input attenuator and feed the signal directly to the RF module (X137) the device seems to at least show a reasonable plot hinting towards a broken input attenuation stage.Might be the same thing with you?

author: JonH88
author_rank: Newbie
timestamp: September 01, 2021, 05:41:57 pm
content: Like you, I checked the function of the input attenuator and the 120MHz reference. Both were OK in my case. The tracking generator and attenuator was working along with the associated electronic attenuator. But the primary local oscillator could not lock. It was strange, I got a sweep a sweep but the sensitivity / range was out by c.55dBm, i.e. I had to insert -55dBm for the trace to read 0dBm. The sensitivity changed with frequency and below certain span (10MHz) the signal disappeared. Internal 714Mhz and 21.4MHz signals were present.See pictures of the error log and sweep with the noise floor averaged and sitting about 55dB above where it should be.My existing spectrum analysers won't measure above 3GHz and without other equipment I could not check the internal 3.5Ghz signals.Apart from the errors with the LO loops not locking etc, the LCD display was dark. I thought it was the cold cathode tubes and I looked at these, they were in fact very bright. I suspected that the actual internal liquid had gone dark due to age and that the unit was kept in a hot environment. I used an external monitor as the display, this worked well!After some time checking I decided to return it to the owner. The original fault had been reported to me as a damaged N-Type input connector but clearly the unit had many more problems. It may well be available on EBay for sale shortly for spares.

author: YetAnotherTechie
author_rank: Regular Contributor
timestamp: September 01, 2021, 06:58:32 pm
content: Have you returned it yet? Would you be able to copy some files from the system, i'm looking for the TG eeprom file backup.The display is normally dark due to the heavy EMI shield, but with age it gets quite dim because of old ccfl lamps. Also the polarizer might be bad, or the EMI screen in front, or both.If it's going to be sold for parts let me know please.