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How do you justify that Q3 and Q4 are short-ciruited? Where in Q3 and Q4 did you measure?
Q3 emitter is shorted to Q4 base for sure. If you measure these two nodes, they have to be the same signal.
i think that kwkam is right , the upper side of r17 has to be connected to ground instead of +15 V.
Q1 - Q4 make together current booster and i dont see incorrect polarity of BJTs but what i see is poorly designed scheme or there is something hidden) :
- Why to boost current if Q1 Q4 limited by 10 kOm resistors ?
- Why the positive feedback is used (via U3A)
If nothing wrong with real polarity of transistos on the bread board , i think, when output of U3B
goes deeply negative so C18 is charged up to 30 V
then if due to positivie feedback U3B changes polarity to + 15 V , then B-C junstion will be under 30 + 30 - 0.6 V which lead to failure of BC junstion on Q4 and then Q3's emitter shorted to -15 and biased by 10 kOm could fail due to max Ic for Q3 .
i think that kwkam is right , the upper side of r17 has to be connected to ground instead of +15 V.
Q1 - Q4 make together current booster and i dont see incorrect polarity of BJTs but what i see is poorly designed scheme or there is something hidden) :
- Why to boost current if Q1 Q4 limited by 10 kOm resistors ?
- Why the positive feedback is used (via U3A)
If nothing wrong with real polarity of transistos on the bread board , i think, when output of U3B
goes deeply negative so C18 is charged up to 30 V
then if due to positivie feedback U3B changes polarity to + 15 V , then B-C junstion will be under 30 + 30 - 0.6 V which lead to failure of BC junstion on Q4 and then Q3's emitter shorted to -15 and biased by 10 kOm could fail due to max Ic for Q3 .
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