blown emitter resistor - replace transistor too?

[Billy R aka DynaFreak]

For a solid state amp, would you normally replace an output transistor if its emitter resistor is blown, even if the transistor appears to test ok? In this case the outputs are SC3856/SA1492. This is a rental bass amp WT800C and I would normally go ahead and replace the outputs, but I wonder if I am being too cautious.

[jrfrond]

Usually, emitter resistors don't open for no reason. The transistor might check good with static testing, but does it give up under current load? Do you a bad driver? Open bias string? An open emitter resistor tells me that the affected side may have been driven driven to the rail. Check the surrounding semiconductors and resistors first. If there are no apparent faults, then replace the resistor and bring the amp up on a variac while monitoring current draw. Standard operating procedure. Can a resistor just open up for no reason? Heck yeah!

[Billy R aka DynaFreak]

thanks, yeah both drivers failed, and I have bad outputs on both sides. since I have the parts in hand I am going to replace them all, and of course check the other parts on the output board before powering up.