Mackie HR824 Service Manual page 19

POWER TESTS
Disable the compressor circuit by shorting together pins 1 and 2 of J12.
Set all of the switches to NORMAL and measure the output power of both amplifiers into
their respective load resistors.
Quickly verify that the output power is as least as follows:
High Frequency amplifier
75 Watts @ 3 kHz into 8 ohms (=24.5 Vrms)
Low Frequency amplifier
110 Watts @ 400 Hz into 4 ohms (=21 Vrms)
Quickly verify that both amplifiers clip symmetrically.
Verify that the OL (overload) LED turns on.
Remove the short from J12 when finished.
WOOFER AND TWEETER TESTS
• Carefully inspect the woofer and tweeter cones for any signs of damage. The
speakers do not have front grills, so any cosmetic damage should be easily
indentifiable.
• Measure the dc resistance of each driver and verify nothing is shorted. The resistance
should be around 6 ohms.
• Carefully and gently check by hand that the woofer moves in and out without any
rubbing or scraping of the voice coil.
• Connect the woofer and tweeter to the HR824 amplifier.
• Conduct a listening test and play some low frequency (30 to1kHz) test tones to verify
the performance of the woofer driver.
• Sweep from 15 Hz to 110 Hz and listen carefully for any air leaks at front and back.
Listen at any screw holes, at the power switch and the leds.
• Tighten any screws, or replace gaskets if required.
• Play some high frequency (2kHz to 20 kHz) tones to check the tweeter.
Listen for crystal clear highs, deep bass from two stories down, and the effervescent,
detail-revealing openness so beloved by Hi-Fi gurus.
Servere ear/hearing damage can be caused by continous exposure to high level sounds.
Take every precaution to preserve your hearing.
J12
19