Mackie profx-12

[DWBUZZ]

I just opened up a mackie profx 12. It had a drink spilled on it by the meters and quit working although it would power up. This is way beyond my meager level of electronic competence. Is there anything I could do with a mulitmeter or have I just purchased some spare parts?

[Enzo]

Leave it open. Is it TOTALLY dry now? And does it still "not work"?



And the big question, what does "quit working" mean? If it powers up, then at least part of it works, and you are now down to certain functions don't happen.

[DWBUZZ]

Its dry now. There is no output on the mains, but there is output on monitor or FX send. input xlr's work and all 1/4 in jacks work except 11/12. Meters show a couple lights constantly no other movement. FX works but selection indicator blinks all selections except #6 it stays steady. No EQ. I looked thru a magnifying glass and there appears to to burnt legs # 11,12,13 on U1 also appears burnt at connection of small board that holds U1-U4 onto main board.

[Enzo]

So a lot of it works, we just have specific problems.

COntact Mackie and ask for the schematic. Have your serial number handy. They will probably ask that you not post it online, but you will have it at least.

Often when op amps dies, they wind up with DC on an output pin. I would start by looking at output pins of my op amp ICs. Be aware sometimes an op amop is used to drive an LED, and DC would be expected. But you can often tell when an IC is in the signal path rather than some other function.

[DWBUZZ]

OK, I'll contact Mackie. Thank you.

[DWBUZZ]

I removed the small pcb that holds the effects U1-4 and that made some difference. Now there is output at the mains and the meters work but no effects and no EQ. I believe the problem is in the effect module but it looks like the traces where the socket, that holds the effects, connects to the main board appear burnt so I don't know if its salvageable and probably not worth the cost to replace it. Maybe I'll just have a mixer with no effects or EQ. Also has sticking EQ bypass, main/mon and break switches. Got the schematics, their almost as small as the micro electronics in the board, not an easy read for me. Confusion is compounded by the fact that different models share portions of the same schematics.

[km6xz]

Can you take a close up of the effects module where the traces/legs are burned and post it here? If a sugary drink spilled in it and it dried without being washed out, it is quietly sitting there corroding more. You can wash it thoroughly with Isopropyl Alcohol that will remove some of the residue and also absorb the water that is likely still liquid in tight places such as under surface mount chips long after the exposed areas are dry.

[DWBUZZ]

I tried to post a picture but was rejected as the file size is too large. (4.87). I did as you said and wiped it all down with Isopropyl Alcohol and it looks alot better. I think now there may only be 1 trace that is damaged and also I see that U49 next to the connector appears burnt. Thanks for the help.