whatelse will blow along with output transistors

[dayking79]

Hi,

whatelse will normally go when the output transistors of an amp blow?

Might seem like a silly question as there are bound to be lots of possibilities but i was thinking that through your experience there is a likelyhood of other components that either made the transistor blow or will have blown along with the transistor.

I have come across a few amps recently that have all got shorted output transistors on one channel and when replaced they still wont work, only the one original unblown channel works.

Suppose what i'm looking for here is a - "when the output transistor(s) blow, always check/replace ..." sort of answer.

Please help!

[jaycee]

Usually driver transistors get it as well as the outputs. Output relays can weld if theres one and a protector circuit tried to activate. Resistors or capacitors in the path of the fault can be damaged.

Really it's impossible to say "just replace these" when an output stage blows. Some amp designs can blow the lot right back to the input stage.

The only way to really be sure is to get a schematic, pull the drivers, test. If they're damaged test the components around them, go to the next stage (VAS for example), pull devices, test. When you start getting to the stages where there's no damage, you get the picture.

[Conrad Hoffman]

What jaycee says. Many/most modern ss amps are direct coupled most of the way through. When something goes, often everything goes. There's no predicting it. Worse, if you just replace the obvious, chances are the amp will self destruct again on power-up. You have to work your way back from output to input, checking *every* device before powering up. Even if the amp doesn't self destruct, the nature of the circuits makes localizing a problem difficult using only in-circuit voltage measurements, so you save time by checking parts before hand, in or out of circuit.

[Mr Evil]

If you have a schematic, it can be helpful to put it into a simulator, simulate the cause of the fault (shorted output or whatever), and view the current through each device under those conditions. This will usually give you some idea of how far back the damage goes.