Disassemble 8496A Step Attenuator - Page 1
Forum section: electronics / repair

author: Tony_G
author_rank: Super Contributor
timestamp: February 07, 2017, 08:25:18 pm
content: Hi All,I picked up a 8496A Step Attenuator and when I tested it the first 10dB section is out of tolerance (actually just over 14dB) so I'd like to see if I can repair it.Before I just start ripping it apart I thought I'd ask if anyone has taken one of these apart because it it's clear to me how they go together (the 355D is very clear - This seems to clip together but I don't want to break the case).Any insights?Thanks,TonyG

author: Berni
author_rank: Super Contributor
timestamp: February 07, 2017, 08:40:11 pm
content: The Signal Path Blog has taken a relay switched attenuator apart and i would assume the RF part is the same.I have taken apart a 13GHz switched attenuator in a Gigatronics synthesizer where one of the coils was getting stuck and managed to fix it by shimming it a bit. The actual RF part might be fixable if its just a bad contact issue by cleaning the contact surfaces. But if one of the actual attenuator blocks inside is blown then its pretty much impossible to fix.

author: Armadillo
author_rank: Super Contributor
timestamp: February 07, 2017, 08:44:07 pm
content: Quote from: Tony_G on February 07, 2017, 08:25:18 pmCan you elaborate what frequency you tested it on.? Can you tabulate the attenuation at 1g, 2g, 3g 4g, 5g etc... I trust you have accounted for other losses.

author: Tony_G
author_rank: Super Contributor
timestamp: February 07, 2017, 08:52:35 pm
content: Thanks everyone - The structure is very similar (if not identical) to what was on TSP - I'm confident that the testing was correct and that there is an issue with the attenuator (it failed from DC to 2 GHz, I didn't bother to test from 2-4Ghz).I'm going to see if I can give it a clean then reassemble and test - Who knows it might work.TonyG

author: Tony_G
author_rank: Super Contributor
timestamp: February 07, 2017, 11:06:31 pm
content: Gave it a clean with Deoxit, reassembled and tested again - Still shows a consistent issue with the 10dB section:Frequency Result0.03 GHz 14.40 dB0.05 GHz 14.41 dB0.10 GHz 14.41 dB0.20 GHz 14.40 dB0.40 GHz 14.41 dB0.60 GHz 14.43 dB0.80 GHz 14.46 dB1.00 GHz 14.41 dB1.20 GHz 14.33 dB1.40 GHz 14.33 dB1.60 GHz 14.29 dB1.80 GHz 14.30 dB2.00 GHz 14.31 dBThe 20db and both 40db sections work. Shame as it works well otherwise - You can't get these as replacement parts unfortunately.TonyG

author: Berni
author_rank: Super Contributor
timestamp: February 08, 2017, 08:19:51 am
content: Yeah then id guess the attenuator block inside is damaged, perhaps somebody put too much power trough it at some point.These manual attenuators can be had for reasonable money on ebay, or do you need the exact replacement because it is part of some test equipment?

author: Tony_G
author_rank: Super Contributor
timestamp: February 08, 2017, 03:35:18 pm
content: That's my thought as well - I have a bunch of step attenuators but all of my 110dB ones are out of spec to a lesser or greater degree - Don't need a specific one other than one that matches the performance of a 355D so I guess I'll keep looking.TonyG