Amp runs fine at B+ under 13.3v. When voltage is increased to about 13.3 volts it goes into protect.
TL494 pin one seems to track the increasing supply voltage. As you increase supply voltage pin 1 will rise to 5v and forces the 494 to shut down when B+ is at 13.3v. At the point of shutting down Pin 3 is at 2v. Pin2 stays at 5v regardless of B+.
Rectifiers are out during this.
TL494 pin one seems to track the increasing supply voltage. As you increase supply voltage pin 1 will rise to 5v and forces the 494 to shut down when B+ is at 13.3v. At the point of shutting down Pin 3 is at 2v. Pin2 stays at 5v regardless of B+.
Rectifiers are out during this.
Back on this. What I said in post #1 is inaccurate.
As the supply voltage increases, the protection led starts to come on when supply reaches about 12.4v.
Power source for the protection led seems to be 494 pin 3 whisch is at 2.5v. Signal passes thru a 1K resistor dropping voltage to 1.7v and led is on. 494 still switching.
At this point Pins 1 and 2 are both at 5v.
As the supply voltage increases, the protection led starts to come on when supply reaches about 12.4v.
Power source for the protection led seems to be 494 pin 3 whisch is at 2.5v. Signal passes thru a 1K resistor dropping voltage to 1.7v and led is on. 494 still switching.
At this point Pins 1 and 2 are both at 5v.
Does the amp work normally other than the protection LED?
At what input voltage does the 494 COMPLETELY stop producing drive pulses?
At what input voltage does the 494 COMPLETELY stop producing drive pulses?
It works normally.
It works all the way up to 14.5v. I do not want to go higher than that. Should I?
It works all the way up to 14.5v. I do not want to go higher than that. Should I?
Is pin 1 below pin 2 for the time up until pin 3 starts to rise?
And after it reaches the voltage on pin 2, it remains there as you continue to increase the 12v supply voltage?
And after it reaches the voltage on pin 2, it remains there as you continue to increase the 12v supply voltage?
Pin 2 is stable at 5v (tied to pin 14 and 16)
Is pin 1 below pin 2 for the time up until pin 3 starts to rise?
Yes
And after it reaches the voltage on pin 2, it remains there as you continue to increase the 12v supply voltage?
Yes, it seems to slowly approach 5v like a cap charging.
Is pin 1 below pin 2 for the time up until pin 3 starts to rise?
Yes
And after it reaches the voltage on pin 2, it remains there as you continue to increase the 12v supply voltage?
Yes, it seems to slowly approach 5v like a cap charging.
It appears that the amp has a regulated power supply and when the target rail voltage is reached, pin 3 starts to rise as the duty cycle is being reduced. All of this is normal for a regulated power supply. I don't know why a protect LED would be connected to terminal 3 if the circuit is as described above.
Are you sure that this isn't the power LED?
Are you sure that this isn't the power LED?
No - the power led is getting energized by the 7812 regulator.
Coming off pin 3 the trace goes to a 1K resistor which services the protection led and also pin 3 is attached to 2 10K resistors dividing voltage to a C3198 emitter and base.
Coming off pin 3 the trace goes to a 1K resistor which services the protection led and also pin 3 is attached to 2 10K resistors dividing voltage to a C3198 emitter and base.
The supply may not be regulated. Try heating or cooling the thermistor to see if that has any effect on the lighting of the LED vs the input voltage.
If the output stage is the same, remove Q42 (or the equivalent in your amp).
Does that change anything?
Does that change anything?