Siglent SSA3021X input protection diode - Page 1
Forum section: electronics / repair

author: Zbych_
author_rank: Newbie
timestamp: September 19, 2021, 08:26:37 am
content: Can someone tell me what diode is used to protect input of SSA3021X spectrum analyzer? I guess due to frequency range it is something with low capacitance.

author: thinkfat
author_rank: Unknown
timestamp: September 19, 2021, 09:03:47 am
content: NXP PZU22B maybe.

author: Zbych_
author_rank: Newbie
timestamp: September 19, 2021, 11:09:22 am
content: Hi thinkfat,I think zener diode has to much capacitance to be directly connected to RF input.Maybe U5 is zener diode, but I would bet GS is switching one (forward voltage is ~0.8V)Package seems to be SOD-723, it is about 1mm long.

author: thinkfat
author_rank: Unknown
timestamp: September 19, 2021, 06:54:19 pm
content: I went by the top mark "GS" and the package. It could be SOD-323F just as well.Edit: well, no. SOD-323 is a bit bigger than what you have there...

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: September 21, 2021, 04:21:32 am
content: My SSA3021X is about 7.4db low..., would it be a problem with one of those diodes being blown... I never really thought to fix it, just got used to error.... but I would be interested in fixing it if it's as easy as to replace the protection diode...

author: thinkfat
author_rank: Unknown
timestamp: September 21, 2021, 06:03:06 am
content: This might fit:https://www.mouser.de/datasheet/2/80/CDSP400_G_RevB966584-2505193.pdfCapacitance is about 3pF when reverse biased with 500mV.It's not the original type, but you might get away with that.EDIT:https://www.mouser.de/datasheet/2/408/BAS516_datasheet_en_20161020-1139675.pdfmight be even better, 0.35pF in SOD-523 package.

author: fzabkar
author_rank: Super Contributor
timestamp: September 21, 2021, 06:39:59 am
content: Quote from: Ordinaryman1971 on September 21, 2021, 04:21:32 amIf it's a protection diode, then the unit should run without it. That should enable you to determine whether it is the problem.

author: thinkfat
author_rank: Unknown
timestamp: September 21, 2021, 09:33:12 am
content: The datasheet capacity might actually not be that relevant, since diodes have smaller capacity when reverse biased. But in any case, I think you can just use any fast silicon switching diode, just search by footprint and select for smallest recovery time ( < 2ns seems to be good).

author: Zbych_
author_rank: Newbie
timestamp: September 22, 2021, 07:40:06 pm
content: I received response from Siglent with diode part number. It is obsolete PIN diode, SCD-80 package.Unfortunately they asked me to not share the number on forum.

author: fzabkar
author_rank: Super Contributor
timestamp: September 23, 2021, 12:54:04 am
content: You can still tell us which diodes are suitable substitutes. ;-|

author: tautech
author_rank: Super Contributor
timestamp: September 23, 2021, 04:06:22 am
content: Might it just be marking code S ?https://www.nxp.com/docs/en/data-sheet/BAP64-02.pdf

author: gamalot
author_rank: Super Contributor
timestamp: September 23, 2021, 12:37:38 pm
content: I guess they are Infineon BAR63-02Vhttps://www.infineon.com/dgdl/Infineon-BAR63SERIES_DS-DS-v01_01-EN.pdf?fileId=5546d4625e763904015ec363284f64d0

author: tautech
author_rank: Super Contributor
timestamp: September 23, 2021, 07:42:29 pm
content: Quote from: gamalot on September 23, 2021, 12:37:38 pmPerfect !S is the date code.Many thanks for coming to the call for help.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: June 10, 2022, 09:28:20 pm
content: F me !! now my SSA3021X is DEAD.. no RF input,I know exactly what happened, an RF unit I was testing with BNC adapter lost its gnd, and the unit was not correctly earthed !!i normally alway have a DC block or attenuator on my analyze, but today i forgot it..waranty is not going to fix it ...anyone tried to fix this ?is it just this diode ?can i measure it ? from the outside ?before i open ?any other parts might be broken ?

author: tautech
author_rank: Super Contributor
timestamp: June 10, 2022, 09:45:13 pm
content: Further recent discussion starts here:https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/msg4228897/#msg4228897Leads to another thread that leads to a video with a RF input ~15dB down repair....all worth a study.

author: Zbych_
author_rank: Newbie
timestamp: July 17, 2022, 11:29:34 am
content: BTW, I've found a video showing front-end repair. Input diodes types are in the video description.It's a pity that Dr Min Zhang didn't put SSA model name in the title, it would be much easier to find.

author: fzabkar
author_rank: Super Contributor
timestamp: July 18, 2022, 07:06:21 pm
content: Fixing and protecting the RF Input of a Spectrum Analyzer (Siglent SSA 3021X):http://emccompliance.co.uk/fixing-and-protecting-the-rf-input-of-a-spectrum-analyzerQuote