Got an amp in with shorted outputs, removed outputs and replaced resistors as needed near the outputs (47ohm, 470ohm, 75ohm, 240ohm only resistors on Q504 side due to failure).
Checked drive signal and Q506 and Q507 checked OK, Q504 and Q505 were dead. Checked signal at 4427 chip and had good signal to pins 2 and 4.
Replaced low-side driver- good drive signal on Q505, Q506, Q507. Q504 starts out with a normal looking square wave but is only dropping to approximately 3 volts when off. After approximately 10 seconds the wave form turns to a flat line with noise at approximately 5 volts.
I'm in the process of tracking down the signal feeding Q516 and Q517.
Any ideas on what would cause the drive signal for Q504 to not come down to near 0 volts. Q501 and Q503 have been replaced.
Checked drive signal and Q506 and Q507 checked OK, Q504 and Q505 were dead. Checked signal at 4427 chip and had good signal to pins 2 and 4.
Replaced low-side driver- good drive signal on Q505, Q506, Q507. Q504 starts out with a normal looking square wave but is only dropping to approximately 3 volts when off. After approximately 10 seconds the wave form turns to a flat line with noise at approximately 5 volts.
I'm in the process of tracking down the signal feeding Q516 and Q517.
Any ideas on what would cause the drive signal for Q504 to not come down to near 0 volts. Q501 and Q503 have been replaced.
For the most part, unless the owner complains about a switch or a pot, I don't even check them. Most don't know how to set them or where they were set before. For the switches, it is more likely to cause problems than anything else. This is for local repairs. When I took repairs in that were not local, I checked switches and often found intermittent switches. I did my best to clean them.
The transistor you found may work. It's a good, high frequency transistor. I was going to recommend the KSA1220A but I could not remember actually using one. I rarely have to replace anything other than the PNP drivers, resistors and the low-side driver IC and those are rare. In virtually every 500 I get, the power supply components and 2 outputs an 2 output transistors are all that I have to replace (I replace all 4 outputs but only 2 generally fail).
The transistor you found may work. It's a good, high frequency transistor. I was going to recommend the KSA1220A but I could not remember actually using one. I rarely have to replace anything other than the PNP drivers, resistors and the low-side driver IC and those are rare. In virtually every 500 I get, the power supply components and 2 outputs an 2 output transistors are all that I have to replace (I replace all 4 outputs but only 2 generally fail).
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