![20180728_120409[1].jpg](/community/data/attachments/629/629715-91cbe4ae1d09a45d12c1d16ddbe2e822.jpg?hash=kcvkrh0JpF)
Decide where the fault lies. Is it oscillating?
Is there +7v and 0v on each output or +3.5 and -3.5 on the outputs etc.
If only one side is not 0v then that is the faulty side.
You are looking for a null on the input of 4080, pin 7. Check C20 for leaking electrically.
Is there +7v and 0v on each output or +3.5 and -3.5 on the outputs etc.
If only one side is not 0v then that is the faulty side.
You are looking for a null on the input of 4080, pin 7. Check C20 for leaking electrically.
the amp is oscillating and it also works.
it is a mono amp so i read the 7V at the speaker terminal.
when i turn on the amp,i only read ~ 4V,it is increasing up to 7V after a few minutes.
in some cases the attached diagram is not really unanimously with my amp.
in the output filter section,i only have 4 caps.the 3 blue ones 106K(C20C,C21C C22C) and one directly at the speaker terminal 22u250V (C210C)
in the diagram is a C19C connected to ground but idont have it on my board.
on the other photo you can see a trace which became hot because of too much current but i dont know what caused that
on pin 7 of the 4080 i read 4,5V DC not 0V.
it is a mono amp so i read the 7V at the speaker terminal.
when i turn on the amp,i only read ~ 4V,it is increasing up to 7V after a few minutes.
in some cases the attached diagram is not really unanimously with my amp.
in the output filter section,i only have 4 caps.the 3 blue ones 106K(C20C,C21C C22C) and one directly at the speaker terminal 22u250V (C210C)
in the diagram is a C19C connected to ground but idont have it on my board.
on the other photo you can see a trace which became hot because of too much current but i dont know what caused that
on pin 7 of the 4080 i read 4,5V DC not 0V.
Attachments
Pin 7 should be 0v. follow the schematic back through IC4 to find the imbalance. It is a differential amplifier and the inputs will explain your odd voltage on pin 7 of the 4080.
Is there 12v ish on the emitter of Q100, does it stay stable.
Both pins 12 and 18 of the 4080 should be an average of 0v but if pin 7 is not the output of 4080 will do odd things.
Is there 12v ish on the emitter of Q100, does it stay stable.
Both pins 12 and 18 of the 4080 should be an average of 0v but if pin 7 is not the output of 4080 will do odd things.
Q100= 12V stable
4080:
pin 6= 4,75V
pin 7= 4,42V
pin 12= 5,05V
pin 18= 5,4V
I have a second one of these amplifiers.it works as it should.
here the pins 6 and 7 of the 4080 are exactely equal,in fact 4,4V
4080:
pin 6= 4,75V
pin 7= 4,42V
pin 12= 5,05V
pin 18= 5,4V
I have a second one of these amplifiers.it works as it should.
here the pins 6 and 7 of the 4080 are exactely equal,in fact 4,4V
So, why are pins 6 & 7 slightly high?
Pin 7 is the DC feedback for the 4080 and if pin 6 is equal to 7 then the outputs will be equal.
Pin 12 & pin 18 are almost equal meaning the DC offset is the difference, which is 0.35volts. Not enough to cause an issue but not zero. The DC offset is measured between the output poles of the speaker, not to ground and a DVM will have trouble reading accurately, as it is chopped DC.
Think of it as a differential amplifier.
What does it read on an oscilloscope? Should average out at zero.
Comparing pin for pin between the good amp and the odd amp will quickly show you where the issue is.
Pin 7 is the DC feedback for the 4080 and if pin 6 is equal to 7 then the outputs will be equal.
Pin 12 & pin 18 are almost equal meaning the DC offset is the difference, which is 0.35volts. Not enough to cause an issue but not zero. The DC offset is measured between the output poles of the speaker, not to ground and a DVM will have trouble reading accurately, as it is chopped DC.
Think of it as a differential amplifier.
What does it read on an oscilloscope? Should average out at zero.
Comparing pin for pin between the good amp and the odd amp will quickly show you where the issue is.
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