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Entry  Mon Jul 30 11:05:44 2018, gautam, Update, SUS, IFO SUS wonky IMG_7102.JPG
    Reply  Mon Jul 30 16:11:54 2018, gautam, Update, SUS, Trillium interface box is broken 
       Reply  Mon Jul 30 18:19:03 2018, Koji, Update, SUS, Trillium interface box was fixed and reinstalled P_20180730_173134.jpgP_20180730_180151.jpg
          Reply  Tue Jul 31 08:17:55 2018, Steve, Update, SUS, Trillium interface box was fixed,reinstalled & working all_OK.png
Message ID: 14118     Entry time: Mon Jul 30 18:19:03 2018     In reply to: 14117     Reply to this: 14119
Author: Koji 
Type: Update 
Category: SUS 
Subject: Trillium interface box was fixed and reinstalled 

The trillium interface box was removed from the rack.

The problem was the incorrect use of an under-spec TVS (Transient Voltage Suppression) diodes (~ semiconductor fuse) for the protection circuit.
The TVS diodes we had had the breakdown voltages lower than the supplied voltages of +/-20V. This over-voltage eventually caused the catastrophic breakdown of one of the diodes.

I don't find any particular reason to have these diodes during the laboratory use of the interface. Therefore, I've removed the TVS diodes and left them unreplaced. The circuit was tested on the bench and returned to the rack. All the cables are hooked up, and now the BRLMs look as usual.


Details

- The board version was found to be D1000749-v2

- There was an obvious sign of burning or thermal history around the components D17 and D14. The solder of the D17 was so brittle that just a finger touch was enough to remove the component.

- These D components are TVS diodes (Transient Voltage Suppression Diodes) manufactured by Littelfuse Inc. It is sort of a surge/overvoltage protector to protect rest of the circuit to be exposed to excess voltage. The specified component for D17/D14 was 5.0SMMDJ20A with reverse standoff voltage (~operating voltage) of 20V and the breakdown voltage of 22.20V(min)~24.50V(max). However, the spec sheet told that the marking of the proper component must be "5BEW" rather than "DEM," which is visible on the component. Some search revealed that the used component was SMDJ15A, which has the breakdown voltage of 16.70V~18.50V. This spec is way too low compared to the supplied voltage of +/-20V.

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