Mackie SWA1501 - PS/AMP Board Troubleshoot or Replace?

[GreggA]

Hi Group - I'm a new member. I'm a BSEE but haven't used my skills for many years. These days I'm a sound engineer.

I've read through this forum and WOW - Tons of troubleshooting info on the SWA1501 -I'm wondering if it's worth my time to component level troubleshoot this thing. I've pulled it apart and the fuses and connections are good and there are no burned components or traces. Speaker reads 12ohms. PreAmp has power and reacts to signal (Signal LED bumps and Limit lights when I turn the input WAY up). The speaker does produce a tiny bit of sound, but it's barely audible.

Has anyone tried to get a replacement PS/AMP board from Mackie? I know this that a lot of the fun/challenge out of things, but since I have no replacement components, is it worth it to check all of the silicon?

Any advice is appreciated.

-Gregg

[Enzo]

Hi, welcome.


We have a loooong thread on that model, various folks have entered and left that discussion. But really, how many posts on that compared to the many more on something like loose resistors in the Fender Hot Rod DeVille?

I am a Mackie repair center, so I fix the things. I once had one so badly burned I could not reliably repair if, so I replaced the powr amp board. Not cheap. BUt all the others, I repaired. Mackie won;t sell YOU a board, I don;t think (you could ask them), but you could probably order one through any MAckie dealer. Assuming they have stock.

But why give up before you start? You got schematics? Isolate the problem. Pull the ribbon between preamp and power amp. Find the pin that carries signal and touch the pin on the power amp. Hum come out the speaker? If so, the problem is in the preamp. If not the problem probably lives in the power amp. You'd feel silly replacing a $400 set of boards for a bad 40 cent op amp in the preamp.

FOllow the circuit analysis in the other thread. There is a pair of high voltage rails for the powr amp, then an extra high voltage rail that flys around with the signal. That fails and you lose a lot. There are a couple sets of +/-15v, and without looking, if I recall, the preamp has its own 15v regulation from some +/-25v sources. I think. In any case, those zenres can fail and kill amplification.

I know I suggested a general check procedure over there somewhere - meter on diode test, and go around the
"hole" in the center and check every transistor hanging into it. The zeners are over in the corner by the ribbon, and also nestled up by the large caps. SO they all have 15v across themselves?