Mackie M1400 Power Amplifier temperature light stay on.

[mwenga]

Temperature light stay on even though the Heat sink is cold as ice.
I have a M1400 amplifier for some reason the temperature light stay on. I checked all my pre amp transistor and the output transistor all seem to measure fine. Also the temperature IC U1 (LM35DZ) it's okay. I have changed the LM339 IC as well . Still no changes. Any suggestions. just posted the Circuit Diagram

[mwenga]

[nevetslab]

What voltage do you have at IC U5 Pin 6? That's the output from the Temp Sensor IC to the input of the Temp Muting comparator. Is the amp in Mute with the TEMP LED on? Can you make the Temp vary by applying heat to the Temp IC U1? I see there are factory test points at that can be applied to the ouput line via resistors R158, R113 & R187. Any chance there's conductive debris in that vicinity? Also, I see there's a capacitor at the output of U1 via resistor R146...a 10uF electrolytic. Any chance that part is bad?

I couldn't read the jpg copy of the schematic you posted, so I've attached the schematics and PCB layouts so they can be downloaded to zoom in on the circuits for the rest of us to ponder it.

MACKIE M1400 SCH.pdf

[Mark Black]

It's getting to be a long time since I was inside one of those, but as I recall that problem always involved the small PCB - either component leads cracked or ribbon cable problems.

Possible clues here as well: SOLVED: I have a second hand Mackie m1400 power amplifier. - Fixya

[mwenga]

thanks Mark, the link you sent seem to have more solution, I will go tackle it looking on those suggestion.

[mwenga]

thank you for the schematic, it will help a lot, as I was not seeing the diagram very well