Electronics > Beginners
Question about the function of a capacitor in a circuit
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xavier60:
Removing output transistors will open the feedback loop. Tack in a resistor from Base to Emitter of one of the missing transistor's pads to keep the loop closed. Use a 1K or else anything from 470Ω to 2.2K.
fedaalis84:

--- Quote from: xavier60 on March 07, 2019, 06:48:46 am ---Removing output transistors will open the feedback loop. Tack in a resistor from Base to Emitter of one of the missing transistor's pads to keep the loop closed. Use a 1K or else anything from 470Ω to 2.2K.

--- End quote ---

Victory! Or at least a partial one.

I don't have any spare resistors around, so I took a 2.2KOhm SMD resistor out of an old broken phone handset & jumpered it with some wires between the base and emitter of the PNP transistor on the right channel.

Boom, I'm getting 2V on the VOUT- pin on that channel. It should be a small negative voltage. But I'm assuming because the VOUT+ circuit is open on that side, it's leaning toward the positive.

In any case... I *THINK* I'm safe to put the transistors in! Wooo.

Will give that a try next.
xavier60:
Did you find a reason for the large voltage difference between the VOUTs on the right channel?
xavier60:
If there really was a large voltage difference between the VOUTs on the right channel, a reason needs to be found even if the problem has seemed to have fixed itself.
It is possibly the reason for the original failure of the output transistors.
fedaalis84:

--- Quote from: xavier60 on March 07, 2019, 02:12:00 pm ---If there really was a large voltage difference between the VOUTs on the right channel, a reason needs to be found even if the problem has seemed to have fixed itself.
It is possibly the reason for the original failure of the output transistors.

--- End quote ---

Nope. Not finding the reason. But there is definitely still a problem, I toasted another set of transistors ;)

I am missing R759 (should be 100ohm) - I put in a ~300 something ohm guy. So not sure of that is the reason.

Voltages were great - everything was great, no protect... Tried out some music on headphones - worked (but the music was scratchy and low volume).

Pulled out the headphones, went into protect. Fried right channel transistors.

Not sure what's up...
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