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Retrofitting Failing Harris SX Transmitter Displays

Michael Patton & Associates sees an opportunity and seizes it

New Michael Patton & Associates Retrofit Display

Original Harris SX Display

Michael Patton and his contract engineering company, Michael Patton & Associates, has made a good living at contract engineering and he’s expanded operations by offering equipment repair. He’s even built upon that by offering some aftermarket products, especially for the popular Harris SX transmitter family.

The latest is a retrofit for the display unit. Patton explains the idea behind this product: “There has been one issue in particular which has dogged every SX series transmitter ever made: the premature failure of the digital alphanumeric displays in the built-in diagnostic display.”

Due to the telemetry systems’ design it displayed a “key” number and a value number. The key number needed to be looked up to be understood. There was also a series of overload codes that could not be understood without a reference guide. When whole digits failed or individual segments went dark erroneous interpretations were inevitable.

Patton explains that the SX had no simple “idiot lights” to announce failures but rather relied upon the display to relate information to the user. Once the display began to fail it became difficult to troubleshoot transmitter troubles. “The only alternative to a functional diagnostic display is for the engineer working on the transmitter to defeat the interlocks and attempt to make direct measurements of internal voltages and waveforms, while the transmitter is actually running. This is an extremely dangerous practice under any circumstances, but especially so since most engineers work alone these days.”

Patton feels that “the failure of this display is the biggest impediment to keeping one of these transmitters running.”

The problem originates with the use of the now obsolete Texas Instruments TIL308 LED display chip. Not completely reliable to begin with, the chip is no longer supported by TI, hence the need for others to step in with usable solutions.

Patton and company have extensive experience with the SX line and plenty of parts. They studied the information collection and display system, figured out the telemetry operation and built a modern interface to handle it. Using an Arduino microcontroller, the result was a new display regime that carries the same required information along with additional source identification info and performance comments based on the transmitter model.

The MP&A LCD-based displays are an improvement over the older, simpler monochromatic red digital segments, with much better resolution and several colors. They should also be more reliable.

Patton says, “Troubleshooting calls and routine logging of parameters are both now much easier with our display. You get a clear indication of what is happening inside the transmitter, while not compromising safety at all.”

He adds that installation of the new workings is simple with the subassembly fitting into the old footprint and the cable interface connection matches the SX’s ribbon cable connector. The original numeric keypads can be used or new ones installed at the same time.