The only thing that affects the 339 output is over/under voltage and the thermal circuit. I don't see any way for the over-current to drive the 339. Is there something that I'm missing?
Lift pin 1 of the LM339. Does the amp still shut down?
Note that this will disable part of the protection circuit and eliminate the mute delay.
Lift pin 1 of the LM339. Does the amp still shut down?
Note that this will disable part of the protection circuit and eliminate the mute delay.
Lifting pin 1 the amplifier continues to play.
Pin 7 is still dropping low. Pin 1 measures .230V and drops to zero as pin 7 goes below pin 6. The pad measures a constant 16V no matter what happens on pin 7. I don't see any significant changes on any of the other pins.
Shouldn't there be about 5V on pin 1 when pin 7 is above pin 6?
Pin 7 is still dropping low. Pin 1 measures .230V and drops to zero as pin 7 goes below pin 6. The pad measures a constant 16V no matter what happens on pin 7. I don't see any significant changes on any of the other pins.
Shouldn't there be about 5V on pin 1 when pin 7 is above pin 6?
The 339 has open collector outputs. They can only drive to ground. To go high, they require a pull-up resistor. With the leg disconnected from the board, there is nothing to pull it up.
So the amp operates absolutely perfectly on both channels with leg 1 lifted?
So the amp operates absolutely perfectly on both channels with leg 1 lifted?
Aside from whatever is making pin 7 go low, the amp seems to work correctly. I'm not finding anything else wrong. I have clean and equal signal all through the 072's on to the output terminals and I'm not finding anything significantly different between the two channels.
No, with D4 lifted pin 7 remains above 9V. Pin 2, 13, & 14 dip as low as 3.9V. Looks like it's because Pin 8 also dips as low as 3.9V
So that's enough to take pin 7 below pin 6 when D4 is in the circuit.
Should reconnect D4 and pin 1 of the 339 and lift pin 14 of the 339 to confirm?
So that's enough to take pin 7 below pin 6 when D4 is in the circuit.
Should reconnect D4 and pin 1 of the 339 and lift pin 14 of the 339 to confirm?
Lift 2, 13 and 14, one at a time (you can leave them disconnected as you lift the others). After lifting each one, do whatever you have been doing to cause the amp to shut down. Can you determine which pin is causing the problem?
Reconnecting D4 and pin 1 will make it easier to see the drop due to the cap that has to recharge.
Reconnecting D4 and pin 1 will make it easier to see the drop due to the cap that has to recharge.
I have lifted each pin individually, with each of the others connected and it is pin 14 causing the problem.
If you leave pin 14 up and reconnect all other components that were removed for troubleshooting, does the amp work as it should?
R21 may be defective or have a bad solder connection.
R21 may be defective or have a bad solder connection.
Amp works as it should with just pin 14 disconnected.
R21, R20, R19, C8, & C10 all have good connection and measure within tolerance.
R21, R20, R19, C8, & C10 all have good connection and measure within tolerance.
If pin 14 is intermittently going to ground and the voltage feeding its inputs isn't the problem, I'd suspect the 339.
Swapping the 339 for another made no difference.
In order for pin 14 to go toward ground, pin 8 must be higher than pin 9?
In order for pin 14 to go toward ground, pin 8 must be higher than pin 9?
Yes but either input could change to make the output toggle.
If you have the tutorial, the puncholderamprepairnotes.htm page has an interactive demo of this type of circuit.
If you have the tutorial, the puncholderamprepairnotes.htm page has an interactive demo of this type of circuit.
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