I have one of these lovelies that is driving me to shear frustration. Presented with blown fuse, shorted output MOSFETS and I found one of the 4800uf PS caps O/C. Simple fix me thinks.
Replaced caps, checked V+/- OK, however noted that the +15V was low sitting at around 10V. -15 sitting at 14.7x. Checked the shunt regulator and associated components and even checked current draw on each supply. 37ma on the - and 41ma on the +. Tried disconnecting various stages on the +15 and nothing really made a significant difference, just progress reduction in load and gradual increase in supply. Even tried a separate +15 supply and it appears to stay at the rail voltage. Double checked for high resistance connections but none found. Ended up installing FETS given V+/- and 15V switched voltages OK. Installed and instant blowing of fuse and FETS. Read about need to change the half bridge driver chip IR2111 as well. New set of Outputs and the driver and fingers crossed, power on and instant failure. No shorts on output, all DC checks according to manual OK.
Suspect it has to be associated with the low +15 rail, but tearing my hair out as to what is the root cause especially when the original failure appears to have been the O/C PS cap.
Note this is the first Class D audio amp I have worked on and while I have repaired a lot of SMPS's and understand the principals involved and can see that the output waveforms from the Half Bridge appear incorrect on the floating side, I am a bit stumped and keep coming back to the +15 rail as being the problem, just can't see the cause.
Any thoughts, words of wisdom appreciated.
Replaced caps, checked V+/- OK, however noted that the +15V was low sitting at around 10V. -15 sitting at 14.7x. Checked the shunt regulator and associated components and even checked current draw on each supply. 37ma on the - and 41ma on the +. Tried disconnecting various stages on the +15 and nothing really made a significant difference, just progress reduction in load and gradual increase in supply. Even tried a separate +15 supply and it appears to stay at the rail voltage. Double checked for high resistance connections but none found. Ended up installing FETS given V+/- and 15V switched voltages OK. Installed and instant blowing of fuse and FETS. Read about need to change the half bridge driver chip IR2111 as well. New set of Outputs and the driver and fingers crossed, power on and instant failure. No shorts on output, all DC checks according to manual OK.
Suspect it has to be associated with the low +15 rail, but tearing my hair out as to what is the root cause especially when the original failure appears to have been the O/C PS cap.
Note this is the first Class D audio amp I have worked on and while I have repaired a lot of SMPS's and understand the principals involved and can see that the output waveforms from the Half Bridge appear incorrect on the floating side, I am a bit stumped and keep coming back to the +15 rail as being the problem, just can't see the cause.
Any thoughts, words of wisdom appreciated.