The adjustment of the scoop is not very good, you get a series of superimposed images.But clairly the positieve and negative side has a greet difference of amplitude.With two identical windings that's alarming.I'm afraid there is someting wrong with the transformer.
It seems that Elvee is on vacation because he didn't react to this threat, that's sad (not for him), he is more expert on SMPS then me.
Mona
It seems that Elvee is on vacation because he didn't react to this threat, that's sad (not for him), he is more expert on SMPS then me.
Mona
Apologies for the poor quality scope images. It's an old scope...but better than no scope! I too worry about the different amplitude coming from indentical windings.
And I'm currently not able to provide an external +/- 32v to do that test, much as I would like to. I only have a one DC supply capable of up to 25v. I'm away for 3 weeks from Thursday so I'll have to resume then. I'll give some thought to whether I can cobble together something I can lay my hands on that might give me better capability to run a +/- 32v test. The resulting test would be intriguing. I'm already thinking ahead that if the transformer is damaged then I'll devise another DC power source for the mixer - it's too good to throw out. But must exhaust other testing first.
Thanks for your time and input.
Steve
And I'm currently not able to provide an external +/- 32v to do that test, much as I would like to. I only have a one DC supply capable of up to 25v. I'm away for 3 weeks from Thursday so I'll have to resume then. I'll give some thought to whether I can cobble together something I can lay my hands on that might give me better capability to run a +/- 32v test. The resulting test would be intriguing. I'm already thinking ahead that if the transformer is damaged then I'll devise another DC power source for the mixer - it's too good to throw out. But must exhaust other testing first.
Thanks for your time and input.
Steve
Hello - I'm back and although I've been on vacation this mixer project has been on my mind throughout! Well I came back with some clear thinking and a plan and I kept in mind your advice JonSnell: "Take each part of the circuit separately and keep an open mind."
It was bugging me that something not in the SMPS was possibly affecting those rails so I purchased and attached matching dummy loads across the -32v, 0v, +32v lines each drawing about 230mA. Both rails settled sweetly at +/-32v (only .1 v apart!). Both secondaries looked good and equal in waveform on the scope. Time to look further elsewhere for what was pulling down the -32v line and causing the imbalance. Plugged the power amp board back in and came back up partly on the VARIAC and it didn't take too long to determine that the left channel power amp module was s/c to the neg rail. Bought a replacement today and after installing it both rails looked good on half and then full mains power. Soak tested for a couple of hours now and tested all functions and everything looks and sounds very good.
Extremely pleased and I learnt a lot. I've never had to get totally into an SMPS before and I'm fascinated by the clever design concepts used. And surely against the odds what are the chances of finding an o/c resistor?! There's a lot of shiny new caps in here going back to the owner! I think I've given a new lease of life to the entire SMPS.
Very much appreciate your time and input when I asked. That was good not feeling totally alone when I hit a corner.
Until the next one...
Steve
It was bugging me that something not in the SMPS was possibly affecting those rails so I purchased and attached matching dummy loads across the -32v, 0v, +32v lines each drawing about 230mA. Both rails settled sweetly at +/-32v (only .1 v apart!). Both secondaries looked good and equal in waveform on the scope. Time to look further elsewhere for what was pulling down the -32v line and causing the imbalance. Plugged the power amp board back in and came back up partly on the VARIAC and it didn't take too long to determine that the left channel power amp module was s/c to the neg rail. Bought a replacement today and after installing it both rails looked good on half and then full mains power. Soak tested for a couple of hours now and tested all functions and everything looks and sounds very good.
Extremely pleased and I learnt a lot. I've never had to get totally into an SMPS before and I'm fascinated by the clever design concepts used. And surely against the odds what are the chances of finding an o/c resistor?! There's a lot of shiny new caps in here going back to the owner! I think I've given a new lease of life to the entire SMPS.
Very much appreciate your time and input when I asked. That was good not feeling totally alone when I hit a corner.
Until the next one...
Steve
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