Overheating surface mount resistors

Introduction

PEM section – Overheating PEM bleed resistors on the CIC-IO board causing discoloration and potential cold solder joints. Apparent cause appears to be incorrect components, since we see this condition in all 2.x PEMs to date.

Components affected are series mounted 23.7k ohm surface mount resistors that will see full battery voltage during excess energy bleed function. If full battery voltage is 410 VDC, then each resistor will dissipate about 0.44 watts.

Part 2

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Images

Corrective Action

Recommended fix includes replacing all resistors on the CIC-IO board with a 45K ohm version reducing the amount of heat generated.