len@syssoft.com (Len Galasso) (10/05/90)
My original posting was a power amplifier exibiting symptoms of asymmetrical output waveforms when attempting to drive output impedances lower than ~60 ohms. I suspected a problem with the balancing of the output transistors or some passive component whose value had become out of tolerance. I received some good feedback most of which was related to the fact the the symptoms were NOT related to any type of balancing or matching of the output transistors. The best suggestion was to check the emitter resitors which are usually a fraction of an ohm or so, high power, and fusible. Well, this was one of the first things I checked in my original troubleshooting; but my mistake was to test them IN THE CIRCUIT. In this case, they tested fine, but in reality, one of them was opened causing only one of the output transistors to conduct, the other half-cycle was being taken care of by the other half's *driver* transistor--one of much less current-capability--so things were find until I tried to really draw some current with a low im- pedance load, then things got wierd. I guess my DVOM was measuring some other resistance path in the circuit which led me to believe that the emitter resistors were ok. Thanks for your input and perhaps I can return the favor. Len Galasso +---------------------------------------+----------------------------------+ | Len Galasso | "No man is an island--but some | | Systems and Software Inc. | are surely peninsulas.." | | len@syssoft.com | ljg | | (714) 833-1700 | | +---------------------------------------+----------------------------------+