Depot solves tactical satellite terminal power supply problem

Army Communicator, Fall, 2004 by Anthony J. Ricchiazzi

TOBYHANNA ARMY DEPOT, Pa.--Two employees here have developed a modification to a high-voltage switching module that dramatically increases the number of high-dollar-value transistors that can be used in that module, improves the performance of the power supply in which it is used and reduces component failure in tactical satellite terminals.

The alternative also will save the U.S. Army more than $2.5 million in its first year of implementation. The terminals, the AN/TSC-94A(V)1 and (V)2, and the AN/TSC-100A(V)I and (V)2, are used throughout the U.S. military.

"Tom Ondrey and Mark Williams identified a problem with the transistors being overhauled here for those terminals," said Sharon Smith, chief of the depot's Research and Analysis Division, Productivity Improvement and Innovation Directorate. "Each transistor would operate OK by itself, but when installed in a power supply's high-voltage switching module, small differences in the transistor switching speed would make the switching module prone to errors."

Williams is an electronics mechanic in the Jam Resistant Secure Communications Division, Satellite Communications Directorate. Ondrey is an electronics engineer in the Production Engineering Directorate's Communications Support Division.

Depot personnel were expending time to test and find transistors that met the stringent performance requirements of the switching modules, driving up the cost of module repair by thousands of dollars.

Williams and Ondrey began searching for a solution in January 2003 by first working with the transistor supplier to begin eliminating possible causes of the problem.

From there, they moved to testing numerous combinations of components at Tobyhanna to find the right one that would allow the transistors to work together properly in the high-voltage switching module.

"We were trying modifications to the circuit card that would allow the transistors to work properly, but not adversely affect the power supply," Ondrey said. "It required a great deal of test data that was very time-consuming to collect and correlate."

"There was a lot of trial and error on the bench," Williams added. "We wanted to find the right combination of components that would work in the high-voltage switching module, but not be detrimental to the power supply."

After testing more than a hundred combinations and analysis that took nearly a year, Williams and Ondrey found the solution--a modification to the switching module circuit card that allows nearly 100 percent of the vendor-supplied transistors to function properly.

"The modification involves replacing a number of resistors with similar resistors that have twice the resistance, but the same size and power ratings as the originals," Ondrey said.

Tests at Tobyhanna revealed that not only did the modification allow the transistors to perform properly in the high-voltage switching module, it also reduced electric current draw and power supply ripple (or noise), thereby improving performance.

"To get test data from the field, we outfitted a power supply with four modified switching modules and took it to an Air National Guard unit at Fort Indiantown Gap," Ondrey said. "With their help, we installed the power supply in a TSC-100A terminal and ran it continuously for more than 230 hours. It ran flawlessly."

"They wrote an Engineering Change Proposal to document the modification and forwarded to CECOM (U.S. Army Communications-Electronics Command) for review and approval," Smith said. "Their proposal was approved and implemented in May and has earned them a significant Value Engineering award."

Mr. Ricchiazzo is with Tobyhanna

Amy Depot Public Affairs Office, Tobyhanna, Pa.