Transmitters!  These days you can put 10kW of FM on the bench to repair.  Fun times. 


Nicom NT250.  In this case the NT stood for “not transmitting”.  


Nicom packs almost everything but the PA on a single board.  That means a lot of labeling, unwiring and disconnecting to remove it.   This time the negative supply voltage failed.  It’s derived from the positive regulator with a series of capacitors and diodes. The capacitors fail and the unit shuts down.  The PA output device had also failed, see below. 

Sometimes you have to dig to find the failed components.  Other times you don’t. 

The ceramic cover was blown right off the FET. 


Fortunately the final device is still available. Not cheap, but available. 

Idle bias current needs to be set. There is a small, flimsy trimpot to adjust it on the RF pallet. Those trimpots are peppered all over Nicom equipment and are trouble.    Also check every solder joint.  The factory apparently doesn’t.