Blew a channel on my mixer (M-520)

[lo.fi.love]

Oops.

I didn't realize that I had been overloading the preamp on a channel for TWENTY MINUTES.

My overhead lamp dimmed and my power conditioner clicked into "sag" mode. I checked the "OL" LED on the channel and it was glaring at me with its beady red eye. My mix did some weird things, and then the line went out. My overhead lamp went from brown back to yellow, and everything went back to normal, save the dead tape input on channel 2.

Lesson learned: Don't get so focused on your mix that you forget to check on your equipment. Ha ha ha.

OK, so my hunch is that I should be able to fix this. Pull the channel card and look for any visibly burnt / damaged components, right? Use the multimeter to check for continuity in several points of the preamp / tape in circuit. Compare against the schematic, and order replacement components.

Does anyone have experience with this sort of thing? I figure I'll have to do some hunting, but I think it's possible to fix this on my own. Thoughts?

 

[sweetbeats]

Am I correct in my assumption that maybe you were hoping I'd post?

M-519...heheh...HAHA! Technoplayer cracks me up!

Glad you can laugh at that too, Jeff.

Listen, I think this is totally something you'll be able to repair. The trick is that in order to easily trace out the problem area you'll need to be able to have the card under power to "tone out" the circuit and see where you lose the tone.

First, as you said of course, pull the card and see if something looks fried, but if it is a cap or an opamp then more often (in my experience) it looks just fine...get out your schematics and follow the path from the TAPE jack and look at each component along the way. If you don't see anything then its time to put some tone into the thing and find the culprit.

I'll do the best I can to help.

The OTHER thing I would do is pull connections from that card (so it is out of the path) and test out everything on the board to make sure the trouble is isolated to that card.

Post back when you have more info.

 

[sweetbeats]

If you don't see any burned up stuff, you can check for continuity across C13 and C48. My prime suspect is U2. That's a 4556 opamp which is a pretty hearty chip so it would take a bit of overloading to cook it...that you'll need to have the card powered to test. Any of the resistors R23, R26 or R100 you'll have to remove one leg and test them with your meter.

Remember there may and likely will be multiple components either cook or at least damaged and worthy of replacement.

That gives you some stuff to go on if you don't see anything cooked.

When you say "overloaded", do you have some idea of the signal strength that was sent to the TAPE IN jack? C48 is only 16V and if you were pumping hefty signal then that could have taken the hit, but the way you describe your lights dimming tells me:

• A, something may be messed with your household power, and
• B, something went straight to ground when it failed which WOULDN'T be the case with C48...this is why I'm suggesting you check out the rest of the mixer. Odd for there to be a failure that draws enough current to dim lights but doesn't blow fuses or throw breakers...

 

[jjones1700]

This saddens me.

Take a perfectly good board and blow it the hell up.

Just giving you a hard time LoFi. I'll gladly take it off your hands if you feel it is too big of a repair for you.