Mackie HR824 THX Auto Off Issue

[saxmonster]

Hello All,

One of my HR824's has a slight issue with the auto on switch.  When you have the switch set to auto, the speaker when first turned on from the front stays off until a signal goes into it and turns it on.  When the signal stops and nothing is running through the speaker it will shut off automatically.  Well this one comes on right away when the main power switch on the front is turned on and it will not turn off at all unless I turn the main front switch off.  So it seems that the auto on and off are not working.  Something is keeping the threshold open.  I have unplugg the xlr running the signal into it but no luck.  I have emailed mackie and they said that it could be the switch or more than likely oxidation has formed and is causing the floor noise to be louder thus triggering the speaker to come on.  Mackie wants me to take it to a authorized shop but if it is something simple I would rather do it.

Does anyone know of any guides or videos to check out prior to opening this beast?  What should I look for beside cold solder joints or oxidation.  What is best used to remove oxidation?  Is there a way I can check for the floor level and what the threshold should be for the auto off?  I have built many kits I just don't have the know how of the science,hahahaha.  Thanks in advance.  I did get a copy of the schematic.

-Scott

 

[saxmonster]

So in reading the service manual it says

"In the Auto ON position, the amplifiers turn on and off depending on the presence or absence of an input signal.  An input signal level or -45dbu (minimum) activates the auto-on function.  A silent period greater than five minutes activates the auto-off function.  The red PWR LED on the front panel reflects the state of the amplifiers."

My speaker never turns off so some noise above the level is keeping it on.  Where can I look for noise at?  I had it opened and saw no bad caps or oxidation at all.  I even left the speaker on with out the input wires connected and it still stayed on.  Something internal is causing noise with in the system that I don't hear coming out of the speakers.  Could the switch be bad?  Everything looks great inside.  What is a good switch contact cleaner to use?  I have worked the switch back and forth to try to clean it but nothing helps.

Here is a link to the manual but no mention where to check for noise, I only have a fluke digital multi meter will I be able to fine the noise with that or do I need a scope?

http://bmamps.com/Schematics/Mackie/Mackie_HR824_Service_Manual.pdf

Thanks
-Scott

 

[PRR]

> a link to the manual

Missing the fold-out schematic.

> some noise above the level is keeping it on

_OR_ some DC leakage in the audio detector.

Personally, I would not tear my hair or pry-open those boxes just for a auto-on failure. Use the On/Off switch. If you need "remote" turn-on, leave the speakers on and plug them into a power-strip near your chair.

 

[saxmonster]

Thanks PRR,

I was thinking the same thing but sometimes I get up and leave the room because something needs my attention in the house.  I just noticed it again yesterday when I left and came back into my project studio and saw that the one speaker was still on.  Just annoying but I will probably just leave it alone and not mess with it like you said.

Thanks
-Scott

PS.  Gonna see if I can find that fold out schematic online somewhere.