[Part identification] Siemens PLC output board repair

[Rutherberg]

Hi,

I'm on a Siemens PLC output board (board ref 812 2298 01-, PLC model Simatic S5-100U), the "fault" led of that board is on when using the PLC. It is not a slot problem, other board worked fine in the same slot.

I identified the faulty part, it is a SMD in parallel with the input cap on the power supply rail, and it is in short circuit.
The package seems to be a SOD-80, marked "2222" all around the part. Probably a surge protection part, but I can't find any informations about it.

Here are some pictures : https://www.dropbox.com/sh/fn01nqzu8qwz9v4/AACLUskmBHj4l6z6YH_wRcdTa?dl=0

Furthermore, the 10A fuse is blown, is there a way to determine if it is a fast acting or a slow blo ?

Thanks !

[goaty]

I guess its a spark gap / overvoltage protection.
Reverse polarity protection is unlikely.

[fzabkar]

The adjacent 22uF capacitor is rated for 50V, so that might provide a clue (a voltage measurement would be better). I'm guessing that the arrestor could be replaced with a transient voltage suppressor, eg a TVS diode, transil, etc. However, I would think that gas arrestors would tend to be more robust and more likely to recover from an overvoltage.

https://au.mouser.com/datasheet/2/315/ABA0000C1151-947454.pdf

[Rutherberg]

The power supply module for this PLC is 24Vdc.
So a TVS of about 35V should do the trick, right ? Or should I narrow it to near 24V ? It's an output module so there is no ultra sensitive parts on that board...

Thanks !

[Brutte]

I'd use something that passes around 1mA at rated voltage.

[fzabkar]

A 24V unidirectional TVS diode will do the job. That's it's standoff voltage. It's breakdown voltage would be considerably higher.

I would consider an SMCJ24A or SMBJ24A or SMAJ24A, depending on the physical dimensions.

https://m.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_smcj_datasheet.pdf.pdf