Mackie 406M Service Manual - page 15
15
Power Consumption
With no signal and no load, the power consumption from the AC mains should be:
Variac Power consumption
Up to 40vac
Up to 60vac
Up to 120vac
DC supplies
Set the Variac up to 120vac (US models)
Measure the DC supplies: (see page 204-4 for the pcb layout)
+69 to +71vdc Q5 Pin 2
–69 to –71vdc Q50 Pin 2
+59 to +61vdc Q10 Pin 2
–59 to –61vdc Q47 Pin 2
+14 to +15.5vdc U1 Pin 3
–14 to –15.5vdc U2 Pin 3
+4.75 to +5.25vdc Across U5 Pins 2 & 3
Bias Adjustment
The bias adjustment is best done when the amplifier has been warmed up. Run it with a music
program into a dummy load until the heatsink is warm to the touch.
The actual adjustment is done with no signal and no load:
Channel 1
Measure the DC voltage between the two pins of J7
Adjust R2 for 19 to 21mvdc,
Seal the pot with a drop of nail paint
Channel 2
Measure the DC voltage between the two pins of J6
Adjust R1 for 19 to 21mvdc
Seal the pot with a drop of nail paint
Power Tests
Continuous Sine Wave Average Output Power, both channels driven (rated power):
180 watts per channel into 4
Ω
from 40Hz to 20kHz, with no more than 0.15% THD
110 watts per channel into 8
Ω
from 40Hz to 20kHz, with no more than 0.10% THD
Check for symmetrical clipping.
Amplifier tests for the 406M/408M/408S
Q1
Q2
Q3
Ch.2 Bias
Pot R1
Q7 Q8
+15VDC
Regulators
+ 5VDC
regulator
-15VDC
U1 U2
Q9
Channel 1 NPN
Channel 1 PNP
Channel 2 NPN
Channel 2 PNP
60 Volt Rect.
Q10
Q4
Q5
Q6
Q44
Q49
Q48
Q45
U5 TH1
D66
J10
J1
Q46 Q47
e c b
e c b
e c b
e c b
b c e
b c e
b c e
b c e
Q50
Q51
Ch.2
Bias test points
J6
Ch.1
Bias test points
J7
Ch.1 Bias
Pot R2
This is the 204 amplifier circuit board, see chapter 204 for more details