Siglent SSA3021X input protection diode

[Zbych_]

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.

[thinkfat]

NXP PZU22B maybe.

[Zbych_]

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.

[thinkfat]

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...

[Ordinaryman1971]

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...

[thinkfat]

This might fit:
https://www.mouser.de/datasheet/2/80/CDSP400_G_RevB966584-2505193.pdf

Capacitance 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.pdf might be even better, 0.35pF in SOD-523 package.

[fzabkar]

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...

If it's a protection diode, then the unit should run without it. That should enable you to determine whether it is the problem.

[thinkfat]

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).

[Zbych_]

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 It is obsolete PIN diode, SCD-80 package.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.

[fzabkar]

You can still tell us which diodes are suitable substitutes. ;-|

[tautech]

Might it just be marking code S ?
https://www.nxp.com/docs/en/data-sheet/BAP64-02.pdf

[gamalot]

I guess they are Infineon BAR63-02V

https://www.infineon.com/dgdl/Infineon-BAR63SERIES_DS-DS-v01_01-EN.pdf?fileId=5546d4625e763904015ec363284f64d0

[tautech]

I guess they are Infineon BAR63-02V

https://www.infineon.com/dgdl/Infineon-BAR63SERIES_DS-DS-v01_01-EN.pdf?fileId=5546d4625e763904015ec363284f64d0

Perfect ! 
S is the date code. 

Many thanks for coming to the call for help. 

[oz2cpu]

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 ?

[tautech]

Further recent discussion starts here:
https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/msg4228897/#msg4228897

Leads to another thread that leads to a video with a RF input ~15dB down repair....all worth a study.

[Zbych_]

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.

[fzabkar]

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-analyzer

Chips need to be replaced:

PIN Diode D31, D33 ------- BAR63-02V（Infineon）
Voltage regulator diode D32, D34 ------- BZX84J-C30（NXP）
GaAs SPDT Switch U1 --------- MASWSS0181TR (M/A-COM）

If it is a Rigol DSA815 unit, chipset is HMC221B