A Technician reports that the Piper Service Manual instructions for testing emergency power supply units used in Piper PA-46 aircraft may be inadequate. This may have caused some of the power supplies to be put in service with less than specified power to drive their emergency instruments.

Narrative

Recently; I had occasion to use the Piper Aircraft; Inc. Maintenance Manual part number 767-005 dated July 2011 to perform a capacity test. [I] discovered that the instructions for testing the capacity of the emergency power supply; may be inadequate; causing some of these power supplies to be put in service with less than specified power to drive the emergency instruments.The test instructions 34-20-00; paragraph-C; Emergency Power Supply; specify that one side of load resistors be connected to certain pins of the power supply connector for the test; but do not specify where to connect the other terminal of those resistors. I contacted Piper Customer Service and spoke to a person who said that he opened their test box and verified which pins to connect the other end of the load resistors to. The resistors were connected [by me] as per those verbal instructions and tested as per the rest of the published instructions. We monitored the current flow through the resistors to verify that a load was actually applied to the power supply during the test.If anyone is using the procedure as printed in the [Piper] manual; there may be emergency power supplies installed in some aircraft that have not actually had loads applied to test their capacity. This could lead to power supplies that do not meet the proper capacity requirements being installed in some aircraft. I recommend that Piper revise the Maintenance Manual (M/M) to eliminate the word 'ground' from the instructions and to specify exactly which pins to make the proper connections needed for this test. I further recommend that operators; who may have these power supplies installed; retest them with a verified correct test to assure the power supplies are airworthy.