Repair of Mackie SWA 1501 Sub Amplifier
Fault - Dead
The Mackie SWA 1501 Sub Amplifier is a quite complex circuit involving a switching PSU a class H Bi Polar output stage combined with a FET output stage,( the Americans refer to class H as class G - see literature on this amplifier) it is overly complex in my opinion, these type of amplifiers are not necessarily the most reliable, or the best sound quality, but they are a cheap route to making a high power amplifier, using conventional circuit architecture would be a lot more expensive to produce, after all what fun it is making something more complex than it actually needs to be, the highly paid Mackie design department have to justify their wages !
The Customer dropped off just the amplifier chassis.
See the relatively small PCBs and mains transformer
You can see below a bunch of blown components, this was the tip of the iceberg as it turned out.
Removing the heatsink clamps reveals 2 bridge rectifiers, 2 Bi polar power transistors, drivers HEXFET transistors and solid state heat sensors
The main PCB removed from the chassis
You can see below after testing numerous components we found loads of things blown, this is to be expected on a design like this, catastrophic failure of multiple devices throughout the board, these were removed and the PCB was given a good clean to get the carbon debris off.
Replacement of all the semiconductors just waiting for some resistors that we did not have in stock to arrive
The main PCB ready to be re -fitted onto the chassis and all the blown components replaced
All back together and powered up you can just make out the low level supply LEDs illuminated
Front view showing power on
This unit took quite a bit of work to bring back from the dead, however it all tested up fine
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