Revised Worksheet

 

FXO INC. Re-Analysis of a Dual Computer with Interface Unit FMEA

 

Item / Function

Potential Failure Mode

Potential Effect(s) of Failure

Severity Classification

Potential Cause(s) Mechanism(s) of Failure

C1 Power Supply Regulation

Open Ckt

Poor Regulation on the Vdd bus. Output of MUX_A signals subject to ringing and droop

IV: Minor

Internal failure, Broken lead, Broken solder joint

 

Short Ckt

No output from MUX_A.

II: Loss of Redundancy: Can't use IU bus A

Electromigration causing capacitor electrodes to short.

 

Change in Capacitance/ Drift

Poor Regulation on the Vdd bus

IV: Minor

Electromigration causes capacitance to change. Or component degrading.

C2 Power Supply Regulation

Open Ckt

Poor Regulation on the Vdd bus. Output of MUX_A signals subject to ringing and droop

IV: Minor

Internal failure, Broken lead, Broken solder joint

 

Short Ckt

No output from MUX_B.

II: Loss of Redundancy: Can't use IU bus B

Electromigration causing capacitor electrodes to short.

 

Change in Capacitance/ Drift

Poor Regulation on the Vdd bus

IV: Minor

Electromigration causes capacitance to change. Or component degrading.

R1 Buffering resistance to protect inputs

Open Ckt

CONTROL1 signal is opened to MUX A input

II: Loss of Redundancy: Can't use IU bus A

Internal failure, Broken lead, Broken solder joint

 

Short Ckt

No effect

IV: Minor

part failure

 

Change in Resistance

No effect for resistance within 25%

IV: Minor

part failure

R2 Buffering resistance to protect inputs

Open Ckt

CONTROL2 signal is opened to MUX A input

II: Loss of Redundancy: Can't use IU bus A

Internal failure, Broken lead, Broken solder joint

 

Short Ckt

No effect

IV: Minor

part failure

 

Change in Resistance

No effect for resistance within 25%

IV: Minor

part failure

R3 Buffering resistance to protect inputs

Open Ckt

CONTROL1 signal is opened to MUX B input

II: Loss of Redundancy: Can't use IU bus B

Internal failure, Broken lead, Broken solder joint

 

Short Ckt

No effect

IV: Minor

part failure

 

Change in Resistance

No effect for resistance within 25%

IV: Minor

part failure

R4 Buffering resistance to protect inputs

Open Ckt

CONTROL2 signal is opened to MUX B input

II: Loss of Redundancy: Can't use IU bus B

Internal failure, Broken lead, Broken solder joint

 

Short Ckt

No effect

IV: Minor

part failure

 

Change in Resistance

No effect for resistance within 25%

IV: Minor

part failure

MUX_A Computer control signal multiplexing

Short circuit between any two adjacent connections

Pin 1 and Pin 2: The buffered control signals from the redundant computers are shorted.

II: Loss of Redundancy: Output from Bus A is wrong, but Bus B is good

Bent pin, broken trace, foreign substance causing the short.

 

Short circuit between any two adjacent connections

Pin 2 and Pin 3: The control signal from buffered Computer 2 is shorted to the MUX_A output. Causes loss of redundancy

II: Loss of Redundancy: Can't use IU bus A

Bent pin, broken trace, foreign substance causing the short.

 

Open circuit on any pin

Pin 1, or 2 or 3: Loss of the Computer control logic on Side A

II: Loss of Redundancy: Can't use Bus A

Bent pin, broken trace, foreign substance causing the short.

 

Input or output stuck hi or low

Pin 1: Stuck input to MUX A input.

II: Loss of Redundancy: Can't use Bus A

Bent pin, broken trace, foreign substance causing the short.

 

Input or output stuck hi or low

Pin 2: Stuck input on MUX A input.

II: Loss of Redundancy: Can't use Bus A

Bent pin, broken trace, foreign substance causing the short.

 

Input or output stuck hi or low

Pin 3: Stuck output, causes loss of Bus A

II: Loss of Redundancy: Can't use Bus A

Bent pin, broken trace, foreign substance causing the short.

 

Simultaneous short on all connections

All the pins on the chip are shorted together

II: Loss of Redundancy: Can't use Bus A

Internal chip failure.

 

Output signal varies by >25%

Pin 3: output varies by >25%, may cause loss of Bus A

II: Loss of Redundancy: Can't use Bus A

Internal chip failure.

 

Parasitic oscillation of outputs

Pin 3: Output oscillates, causes loss of Bus A

II: Loss of Redundancy: Can't use Bus A

Internal chip failure.

MUX_B Computer control signal multiplexing

Short circuit between any two adjacent connections

Pin 1 and Pin 2: The buffered control signals from the redundant computers are shorted.

II: Loss of Redundancy: Output from Bus B is wrong, but Bus A is good

Bent pin, broken trace, foreign substance causing the short.

 

Short circuit between any two adjacent connections

Pin 2 and Pin 3: The control signal from buffered Computer 2 is shorted to the MUX_B output. Causes loss of redundancy

II: Loss of Redundancy: Can't use IU bus B

Bent pin, broken trace, foreign substance causing the short.

 

Open circuit on any pin

Pin 1, or 2 or 3: Loss of the Computer control logic on Side B

II: Loss of Redundancy: Can't use Bus B

Bent pin, broken trace, foreign substance causing the short.

 

Input or output stuck hi or low

Pin 1: Stuck input to MUX B input.

II: Loss of Redundancy: Can't use Bus B

Bent pin, broken trace, foreign substance causing the short.

 

Input or output stuck hi or low

Pin 2: Stuck input on MUX B input.

II: Loss of Redundancy: Can't use Bus B

Bent pin, broken trace, foreign substance causing the short.

 

Input or output stuck hi or low

Pin 3: Stuck output, causes loss of Bus B

II: Loss of Redundancy: Can't use Bus B

Bent pin, broken trace, foreign substance causing the short.

 

Simultaneous short on all connections

All the pins on the chip are shorted together

II: Loss of Redundancy: Can't use Bus B

Internal chip failure.

 

Output signal varies by >25%

Pin 3: output varies by >25%, may cause loss of Bus B

II: Loss of Redundancy: Can't use Bus B

Internal chip failure.

 

Parasitic oscillation of outputs

Pin 3: Output oscillates, causes loss of Bus B

II: Loss of Redundancy: Can't use Bus B

Internal chip failure.

 

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