Radio Broadcast Technical Consulting and Sales
 10032 Island Drive, Brainerd, MN  56401

Those who work on Harris MW-1 or MW-1A AM Transmitters will recognize these 14-inch long power amplifier modules.  It takes twelve of these to equip a transmitter to run at 1000 watts.  Each module has two RF transistors and five audio transistors.  Depending on conditions, it is expected that there will be one module failure on average per year in these transmitters.

We repair these modules by first checking each of the transistors for gain and leakage when each device one has been removed from the circuit.  Just checking for a short in the transistors is not enough as some of them go open, and will not show a short.  Then, we check for any shorts across the insulators under each transistor.  Careful attention is paid to putting just the right amount of silicone-based heat transfer compound on both sides of the insulators.  We also check the diodes and fuse.  Any replacement components are checked before installation.     

When we repair modules for clients, the charge is about an hour of shop time plus parts.  Module repairs typically cost the client $100 plus shipping.  We have a better than 98% success rate in the repair when they are not actually tested in an MW-1 transmitter before they ship.  We charge an additional $85 to test a module or modules in a working transmitter because it involves driving to a transmitter to do the test.  That makes a lot of sense if we are repairing more than one module at a time.

When reinstalling one of these modules in a transmitter, we recommend making sure it is fully pushed down into the edge-connector socket.  Then, both top mounting screws need to be snug, but not over tightened.  Too tight and the screw will break or strip the threads.  These screws are the RF connection to the transmitter chassis.  Failure to tighten these two screws will result in burned contacts on the bottom edge-connector and socket.  Repairs are definitely more expensive then.     

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   Ham WØMH