Have a Vintage sanyo receiver with no audio/channel hum on left front channel. Traced goo audio from the preamp board to the amp board. Amp board schematic attached. Pin Voltages on the main Amp IC are (with right channel included as a comparison):
Pin L R
1 GND GND
2 45.8 22.9 Pin to 1000uf coupling cap
3 46.3 46.3
4 45.8 35.1
5 N/A
6 N/A
7 10.1 23
8 45.8 23
9 18.9 22.9
10 44.5 44.5
Good audio and voltage (12V) at the TR5 emitter output. But on the other side of C503 at input pin 8 of IC501 (STK STK0231), it jumps to 45.8v, when it should be 24v. Also with pins 2 & 4 also at 45.8V, it makes me think that IC501 is fried. Thoughts? I want to be 100% sure not missing anything since that's a $25 part replacement. I've checked all the resistors and caps and they all seem good and in spec. Also weird is the Pin 9/7 combo. Should be 24v on both pins but on Pin 9 is 18.9, then on the other side of R 513 it's 17.9, then on the other side of C511 it drops to 10.1v. R513 checks out ok and I even swapped C511 to be sure (no difference).
Pin L R
1 GND GND
2 45.8 22.9 Pin to 1000uf coupling cap
3 46.3 46.3
4 45.8 35.1
5 N/A
6 N/A
7 10.1 23
8 45.8 23
9 18.9 22.9
10 44.5 44.5
Good audio and voltage (12V) at the TR5 emitter output. But on the other side of C503 at input pin 8 of IC501 (STK STK0231), it jumps to 45.8v, when it should be 24v. Also with pins 2 & 4 also at 45.8V, it makes me think that IC501 is fried. Thoughts? I want to be 100% sure not missing anything since that's a $25 part replacement. I've checked all the resistors and caps and they all seem good and in spec. Also weird is the Pin 9/7 combo. Should be 24v on both pins but on Pin 9 is 18.9, then on the other side of R 513 it's 17.9, then on the other side of C511 it drops to 10.1v. R513 checks out ok and I even swapped C511 to be sure (no difference).
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