Hi guys I picked up an early punch 40 dsm
landmine style amp today, one channel plays
low with considerably less output than the other?
When adjusting the gain pot for the low channel there is only a slight gain when turned to fill power.
Another thing to note is the volume on the low channel adjusts when the gain pot on the working channel is adjusted?
landmine style amp today, one channel plays
low with considerably less output than the other?
When adjusting the gain pot for the low channel there is only a slight gain when turned to fill power.
Another thing to note is the volume on the low channel adjusts when the gain pot on the working channel is adjusted?
Look on the audio driver board right behind the RCA jacks and see if any of the aluminum 10uf 16v caps are leaking. If you see corrosion or dark fluid on the board that is your problem.
Remove the board and remove all the caps, clean the board thouroughly and check for damage to any traces from the fluid in the caps.
If there is no trace damage, replace the caps and re-install the board. Test it for audio. LMK the result.
Remove the board and remove all the caps, clean the board thouroughly and check for damage to any traces from the fluid in the caps.
If there is no trace damage, replace the caps and re-install the board. Test it for audio. LMK the result.
The caps are the silver metal cans. They are notorious for causing problems but they look clean on the preamp board. You can see it better so you'll have to determine if there is any corrosion.
The same caps can cause problems throughout the amp and to make the amp reliable, long term, you may have to replace all of them if any have begun to leak.
The resistor is part of the feedback circuit. Is the one on the other side (R133) similarly discolored?
If you touch the fluid on the board with your soldering iron and it smells like anti-freeze (or some say it smells like fish), it's electrolyte and the cap near it will need to be replaced. You'll need to clean the residue with solvent (acetone works best but alcohol will also work).
Dive a 100Hz signal into the amp and measure the AC voltage on pins 8, 12, 17 and 18 of the preamp board. Post the voltages. Have the gains set the same for both channels. Set the input level from the signal source so that you read at least 0.1v AC on pins 8 and 12. Place the black probe on the RCA shield when taking the readings.
The same caps can cause problems throughout the amp and to make the amp reliable, long term, you may have to replace all of them if any have begun to leak.
The resistor is part of the feedback circuit. Is the one on the other side (R133) similarly discolored?
If you touch the fluid on the board with your soldering iron and it smells like anti-freeze (or some say it smells like fish), it's electrolyte and the cap near it will need to be replaced. You'll need to clean the residue with solvent (acetone works best but alcohol will also work).
Dive a 100Hz signal into the amp and measure the AC voltage on pins 8, 12, 17 and 18 of the preamp board. Post the voltages. Have the gains set the same for both channels. Set the input level from the signal source so that you read at least 0.1v AC on pins 8 and 12. Place the black probe on the RCA shield when taking the readings.
They are generally all 10uf@16v. You can use standard caps but there's no point. The hardest part is getting the old SMD caps off of the board without damaging the pads. Replacing them is very easy (on the main board, it's more difficult on the preamp board because they're so close together). If there is no corrosion on the preamp board, I'd leave them alone for now.
Post the voltages.
Post the voltages.
Well those were your power supply fets. You might have shorted outputs.
You need to replace the 2 power supply fets, the power supply fet gate resistors, and the power supply drivers.
Test the output fets and make sure they are not shorted.
Your first priority now is to get the supply up and running, you can do no further testing until the amp will power up.
You need to replace the 2 power supply fets, the power supply fet gate resistors, and the power supply drivers.
Test the output fets and make sure they are not shorted.
Your first priority now is to get the supply up and running, you can do no further testing until the amp will power up.
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