Hello all!
I have a punch 800a2 which plays music but is slightly distorted.
With higher frequencies it gets more audible , on the scope there is crossover distortion. the same like turning the bias pot completely CCW.
The amp draws only 1 A and the current didnt get higher when turnin clockwise.
Usually if set correct, it will draw around 2-3 amps.
What can cause that no bias setting is possible?
Best regards!
I have a punch 800a2 which plays music but is slightly distorted.
With higher frequencies it gets more audible , on the scope there is crossover distortion. the same like turning the bias pot completely CCW.
The amp draws only 1 A and the current didnt get higher when turnin clockwise.
Usually if set correct, it will draw around 2-3 amps.
What can cause that no bias setting is possible?
Best regards!
What work has been done to the amp?
What's the DC voltage on the output of the two 15v regulators?
What's the DC voltage on the output of the two 15v regulators?
i really dont know, but it looks like that topaz diode has been changed and a trace fix.
I have measured the 51 ohm resistors from the outputs. One is around 48 ohm instead of 51 out of circuit. Should i replace it?
It's not causing the bias problem but it is out of tolerance so, technically, it should be replaced.
With a load on the speaker output, is the distortion only crossover distortion?
With a load on the speaker output, is the distortion only crossover distortion?
Hi!
Not all Voltages are present and as printed in the circuit ( 15 and 17V ) is 19,4V and 20,8V )
Here are the voltages is had, it seems that the left channel is correct, but right channel has no +15V, its -2,X V.
I measured voltage on C305 , there is just -2,2V. Its weird, in the schematics it should be 100uF 50V ,but there is a electrolytic SMD CAP 10uF 16V installed.
Looks like its original.
Do you have another revision of the diagram so i know what to put in there?
Thanks in advance !
Not all Voltages are present and as printed in the circuit ( 15 and 17V ) is 19,4V and 20,8V )
Here are the voltages is had, it seems that the left channel is correct, but right channel has no +15V, its -2,X V.
I measured voltage on C305 , there is just -2,2V. Its weird, in the schematics it should be 100uF 50V ,but there is a electrolytic SMD CAP 10uF 16V installed.
Looks like its original.
Do you have another revision of the diagram so i know what to put in there?
Thanks in advance !
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According to the values of the programming resistors for the regulators, ±20 is correct. If you use the RCA shield as the meter reference, you'll likely get those voltages.
I don't see R37. I've attached the diagram I'm using.
I don't see R37. I've attached the diagram I'm using.
R37 is on top of the power suppy diagram. But values are different on some resistors.
i installed a 10uF 16 V on C305 but it changed nothing.
I dont know why, but now there is DC on R- and ground, sometimes -32V and sometimes -53V.
With a speaker connected the cone moves a lot and then amp shuts down, supply voltage goes down because of too much current.
R383 has -53V and the other terminal has -27V
i installed a 10uF 16 V on C305 but it changed nothing.
I dont know why, but now there is DC on R- and ground, sometimes -32V and sometimes -53V.
With a speaker connected the cone moves a lot and then amp shuts down, supply voltage goes down because of too much current.
R383 has -53V and the other terminal has -27V
Do you still have significant DC voltage across the right channel if you connect a wire jumper across C5?
Hi!
When i jump C5 there is no change. I tried to jump C305 and then the DC on the outputs disappears.
When i jump C5 there is no change. I tried to jump C305 and then the DC on the outputs disappears.
Why C305?
If jumping C5 didn't eliminate the offset, you likely have a defective output transistor or driver (I'm assuming that you've checked all of the resistors in the output stage near the outputs).
If jumping C5 didn't eliminate the offset, you likely have a defective output transistor or driver (I'm assuming that you've checked all of the resistors in the output stage near the outputs).