Mackie M 1200

[Bruce Koe]

Hello Tech Guys,
We have a Mackie M1200 Power Amplifier for PA and Music at our Neighbors Link Stamford (CT) (immigrants community center). At our last engagement we had a four piece band and about 45 minutes into the performance our left channel (speaker) stops functioning. The M1200 (AF17316) was quite hot and I felt that one channel had overheated. About 5 minutes later it started working again...but I didn't feel any air coming out of the side vents or front of the unit.
So yesterday I took off the cover and powered it up and found that the fan in the center of the unity was not working. Does the M1200 have to come up to temperature for the fan to come on? If not, I am hoping that replacing the fan (7043B) will be the remedy to get us going again. And how do you get to the screws to take the fan off...they look like they are inside the air duct.
Thanks for you knowledge and comments please.
Bruce Koe Bruce@thekoes.com

[flyingdutchman]

The M1200/1400 has its fan controlled by a temperature sensor on the heat sink. Anyway, it should run at low speed even if the unit is cold. When the unit gets warm the fan switches to full speed. When the heatsink gets over 80°C, the amp's output relays are switched off which results in a muted amp - and a warning light on the amp's front panel IIRC.

There's a few points in your report that are in conflict with how the amp should behave:
1) When the amp "thermals out", it should mute BOTH channels, not one channel only
2) If the fan does not run, it will take a lot longer than 5 minutes for the amp to cool down enough so that it returns to normal operation.

As far as point 2) goes, it may be that the fan is worn such that it will not run at low speed but will start moving when commanded to run full speed. I've seen a few fans behaving this way, last one was in a computer power supply with a variable speed fan.

[Bruce Koe]

Thanks FlyingDutchman

the m1200/1400 has its fan controlled by a temperature sensor on the heat sink. Anyway, it should run at low speed even if the unit is cold. When the unit gets warm the fan switches to full speed. When the heatsink gets over 80°c, the amp's output relays are switched off which results in a muted amp - and a warning light on the amp's front panel iirc.

There's a few points in your report that are in conflict with how the amp should behave:
1) when the amp "thermals out", it should mute both channels, not one channel only
2) if the fan does not run, it will take a lot longer than 5 minutes for the amp to cool down enough so that it returns to normal operation.

As far as point 2) goes, it may be that the fan is worn such that it will not run at low speed but will start moving when commanded to run full speed. I've seen a few fans behaving this way, last one was in a computer power supply with a variable speed fan.

thanks flyingdutchman. I really appreciate the info. Is the fan run with 120vac. I can test to see if it works at either of the two speeds you indicate by disconnecting and hot wiring.
To replace the fan there are four screws i can see holding it into the central heat sink but the heads of the screws are internal to the airway. Is there some trick to getting the fan out for replacement?
Will i have to go to mackie for the replacement part to get the right direction of rotation, capacity, dual speed features?
Thanks again for your valuable help. Bruce

[flyingdutchman]

Is the fan run with 120vac. I can test to see if it works at either of the two speeds you indicate by disconnecting and hot wiring.

No, the fan is run with a DC voltage coming from the small circuit board attached to the heatsink just to the left of the fan (looking at the amp with front panel facing you). At low speed, the fan voltage would be 14V, at high speed, 28V. Don't put 120Vac on it, the result won't be pretty
If you're handy with a multimeter/tester you can check if the fan gets power by probing the leads at the connector to the circuit board. If it doesn't get power, the fan might be OK and the problem might be with the circuit.

Is there some trick to getting the fan out for replacement?

The fan is not directly bolted to the heatsink, there's a little sheet aluminum "box" in between. It has screws on the sides. Remove the screws and you can pull out the box and the fan, then unscrew the fan from the box.
Note the orientation of the fan (which side is back/front), usually on one side of the fan frame is a pair of arrows indication the direction of rotation and the direction of airflow.
Check if the fan turns freely. Such may be impeded by dust and dirt deposits, if so, try cleaning the fan - take dust cake off with a brush, and wipe with a cloth and some alcohol.

Will i have to go to mackie for the replacement part

First make sure the problem is with the fan and not the circuit that powers it.
It's nice if you can get the Mackie replacement part, but similar fans are available from companies such as Mouser and RS. You need a 24Vdc, 80mm fan. A generic fan of this type should have sufficient air flow. You probably have to cut the connector off the old fan and fit it to the new one.