Mackie SRM150

[lowell]

Hey there Enzo, and anyone else who is a Mackie service center. This thing came in pulsating, and no sound came out to the speaker. I ruled out the speaker. I then began to narrow down where the issue is - PS, PA, preamp etc... When I disconnected the PA and preamp from the PS the thing began moaning high-pitched. It then went up in smoke. Whoops! I can now see that R11 in the PS is burnt.

SO, I'm curious if you know why this happened. I wouldn't predict that disconnecting the load on the PS would cause the PS to burn up.

Of note is the "MODE" connections. The datasheet for the TDA8920 says it dictates whether the IC is in stby, mute, or ON. I wouldn't think this'd have anything to do with the supply frying.

[lowell]

From Enzo (PM)

"No, I would not expect pulling off the load would hurt the SMPS. Nor do I see much of any reason for R11 to burn up. If C8 or IC1 was a dead short, maybe,,,"

[lowell]

Oke doke. I was removing the PS board to replace R11 and diode D6 fell off the board. Since secondary side components are usually culprits of a "ticking" SMPS I resoldered this, replaced R11 and hoped that it'd be fixed. Well, the thing powers on great now. No clicking. Voltage rails seem good too. Just no sound, at all... DEAD. So I'm gonna take the PA board out and have a looksy. Possibly end up replacing the output IC.

[Enzo]

Power supplies often fail for reasons, so if your SMPS was damaged, the PA is a good first suspect.