Re: Mackie SRM450: 120hz hum with no signal from audio input...

I mean, of course you can test a cap with the ohm setting to see if it's open, but can you test for it's value?

Re: Mackie SRM450: 120hz hum with no signal from audio input...

I get mixed readings with the old rectifiers, and the capacitance function on my multimeter simply doesn't work :-\

So while I work on getting a new meter and the parts are only a few bucks anyway, I'll just shoot for replacing them.

Re: Mackie SRM450: 120hz hum with no signal from audio input...

Referencing page 6 of the schematic I posted, I get these results:

45v- is: -46.3v actual
45v+ is: +46.3v actual

80v- is: -93.6v actual
80v+ is: +93.5v actual

15v+ is: +14.2v actual
15v- is: -14.2v actual

I've got the 2 main rectifiers, "D55" and "D56" in the mail, as well as the 4 filtering caps near the 15v + and - (C157, C158, C156, C165).

Hopefully that'll solve this problem. I'll keep you posted on...

Re: Mackie SRM450: 120hz hum with no signal from audio input...

Awesome! Thanks for the responses everybody. I'll do all of the above and report what I find out.

I'm working on a 2-way 15" powered speaker: Mackie SRM450.

At a show, it slowly lost volume until it stopped working. Opened it up: blown fuse. Threw in another fuse, turned it on and immediately blew it as well.

Tested both rails (one for high pass and one for low pass) and pretty much the entire low pass rail had shorted rectifiers and transistors.

Swapped the entire blown rail along with the 1/4 watt resistors on the low and high pass sides (probably overkill) as well as all of the larger resistors connected to the rail. Also swapped the (4)...

Re: New Members - please post your introductions here

Hey everybody! I am a full time musician that provides live sound/lighting and also DJs weekly in various clubs. I repair all of my own gear, and hope to "gain" some knowledge from friends on here. See what I did there?