Power Supply Failures

Gideon Analytical Laboratories performed failure analysis on several Bias BPS2-07001 failed power supplies. Several good units were submitted for comparison. These Bias BPS2-07001 are linear and switching power supplies 2W 14V, 5V DUAL 85-265V Std Temp and are ROHS compliant. They provide up to one-half, one, or two watts of output power (BPS0.5, BPS1, and BPS2) at 8 or 14 VDC (Vo) and an optional 3.3 or 5 VDC (Vr) output to power standby functions such as clocks, microprocessors, remote control sensors, and more.

The Bias power supply unit is shown in the picture above left. The plastic housing and silicone encapsulation were removed to expose the circuitry. One capacitor was removed and disassembled. The canister did not vent through the score marks and the sleeve was not severed from internal pressure. The picture at the top right is of the rubber seal. The normal seal material is an IIR (isobutyl and isoprene rubber). This seal had a pitting edema, caused by solvent absorption, which indicates the rubber may be an ethylene propylene diene monomer (EPDM). EPDM is not acceptable for use on electrolytic capacitors.

The element was removed from the aluminum canister. The element was extremely dry and the polyethylene tape was partially melted. The Kraft paper was a manila color the same as a new would be. This indicates the element heating occurred in a short period of time or heating was from an external source (process, assembly) as opposed to the application. Heat from an external source will not discolor the Kraft paper but will evaporate the solvent. If the heat were generated from the application, the Kraft paper would turn dark brown. The final conclusion was that the capacitor was failing due to excessive heat.

Gideon Analytical Laboratories can provide electronics companies invaluable information by performing failure analysis. Failure analysis can determine whether a device is failing because of a problem with production or assembly or if the failure has its origins in field application. This information can be extremely useful to a variety of companies in the electronics industry and can help save them enormous amounts of time and money especially if field rollover might be incurred due to the problem.

PCB with power supply unit

PCB with power supply unit

Electrolytic Capacitor Seal

Electrolytic Capacitor Seal