Hi all, I have a Punch 40 DSM on the bench
Which powered up but no audio, there was evidence
of cap leakage around the 10uf 16v smd caps.
So I replaced the lot including the ones on the upright board.
The amp plays nice and clean on the right channel but low on the left channel. It also plays audio via the left channel when only the right channel input is connected?
I've gone through all the new caps and checked for bad connections and they're all good.
There's no signs of overheating or excessive current draw, any ideas on troubleshooting this one appreciated thanks
Which powered up but no audio, there was evidence
of cap leakage around the 10uf 16v smd caps.
So I replaced the lot including the ones on the upright board.
The amp plays nice and clean on the right channel but low on the left channel. It also plays audio via the left channel when only the right channel input is connected?
I've gone through all the new caps and checked for bad connections and they're all good.
There's no signs of overheating or excessive current draw, any ideas on troubleshooting this one appreciated thanks
Do you see the same symptoms on the output pins of the input board and on the input pins of the driver board as you're seeing on the output terminals of the amp?
You'll have to compare levels for the 2 channels to see where the signal is being lost. See attached.
As you know the board is difficult to get to, I've just removed it and checked all the traces they're all good, can I test the signals any way with the board removed?
Why is the board difficult to get to?
If the RCA jacks are in the way, remove them and reconnect with jumper wires.
If the RCA jacks are in the way, remove them and reconnect with jumper wires.
I tested the board on its own and pins 5,6 and 7 had low distorted output compared to 13, 14 and 15
I powered up the board as per the schematic with an audio signal input and tested the output pins for audio via a small spare amp and speaker.
Out of the board, there is no feedback for the gain op-amp. What did the signal look like on U3A pin 1 and U4A pin 1?
U3A
Pin 1 no audio
Pin 3 clear audio
U4A
Pin1 clear audio
Pin 3 clear audio
Note Pin 3 audio on U3A is louder than pins 1 and 3 of U3A
Pin 1 no audio
Pin 3 clear audio
U4A
Pin1 clear audio
Pin 3 clear audio
Note Pin 3 audio on U3A is louder than pins 1 and 3 of U3A
So I re installed the input board and have clean audio on pins 5,6,7, 16 and 17.
Pin 18 is distorted
Audio Signal on legs of left gain pot is also distorted
Pin 18 is distorted
Audio Signal on legs of left gain pot is also distorted
I think U4A is defective, when I heat it up with a hot air iron the sound increases albeit with distortion.