Guru
Joined: 11/02/2018
Location: AustraliaPosts: 3313
| Posted: 07:16am 16 Jan 2023 |
After reading the description of Q3 & Q4 I see they act directly on Q1 & Q2 not via Q7.
Q1 running at full current suggests Q2 could be short circuit. With power off measure its C-E resistance.
With F1 removed the amp is unbalanced and most voltages will be wrong as R20 feeds the error back to Q7 and around the whole amp. Remove F2 as well.
Power up and measure the voltage at R16, terminals 9 & 10. If the rest of the amp is working (input grounded) it should be close to 0V and voltages around Q7, 8 & 9 should be similar to the good amp.
If Q1 is ok and the voltages around Q8 are wrong check it's C-E resistance, compare with other amp Q8.
Edit.
With no speaker connected Q1 can only get hot if Q2 is shorted as then the only current path for Q1 is through Q2.
Edited 2023-01-17 08:07 by phil99