RELIABILITY DESIGN REVIEW OF MIXER-FILTER MX-7.
PHILCO CORP PALO ALTO CALIF
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The design of the MX-7 Mixer-Filter Unit is reviewed. The MX-7 differs from the MX-5 version which it replaces only by the addition of noise gate circuitry. The noise gate introduces an additional 15 component parts in a total of 252 parts required for the complete unit. The MTTF of the MX-7 is predicted to be 6300 hours based on component part failure-rate data available in applicable literature. Electrical stress level measurements and a specified ambient operating temperature of 55C are taken into account in selecting the failure rate figures. Necessary circuit complexity prohibits the attainment of the MTTF design goal of 20,000 hours. In the previous design review of the MX-5, it was recommended that the 50,000 ohms Bourns Trim Pot be replaced with one of less than 20,000 ohms resistance because of the fragility of the fine wire required for the higher resistance. A similar design weakness exists in the MX-7 Mixer-Filter. All component parts were found to be operating well below the maximum rated stress-level specified by the various manufacturers. However, a statement on the acceptability of the MixerFilter Unit by the Reliability Assurance Staff cannot be made until all questionable component parts have been qualified. Author