Adcom GFA-555MS - Manual (Page 15)

damaging the fuse holder. DO NOT FORCE THE FUSE-HOLDER CAP INTO THE
THREADS. Seating of the cap in the fuse-holder body should be easily accomplished
without excessive force.
AC ON/OFF SWITCH
The AC ON/OFF switch controls power to the power transformer and circuits of the
GFA-555ms. Whenever the GFA-555ms is energized, the red POWER LED will glow. Push
the top of the rocker switch to energize the GFA-555ms. Push the bottom of the rocker
switch to turn the unit off.
POWER LED
This LED will glow whenever the AC ON/OFF switch is turned on and the GFA-555ms is
energized. If the AC LINE FUSE blows, the POWER LED will cease to glow.
The POWER LED indicates that there is AC voltage being fed to the amplifier, but it does not
signify that all the amplifier's circuits are in operation. If, for example, you have blown one or
more of the DC RAIL FUSES., the amplifier will not operate - that is, the amplifier will not
produce any audio signal - even though the POWER LED glows. Similarly, if the THERMAL
PROTECTION LED glows, the amplifier will not produce sound even though the POWER
LED may still glow.
Additionally, the internal power transformer is provided with a thermostat which will interrupt
power into the transformer if its temperature exceeds 125°C. This high a temperature will
seldom, if ever, be encountered unless the amplifier is subjected to abnormal conditions,
such as operation into loads of less than 1 ohm at very high listening levels, etc. If the
POWER LED does not glow, the THERMAL PROTECTION LED is out and both the DC
RAIL FUSES and AC LINE FUSE are intact, the indication would be that the thermostat
within the transformer has opened.
Once the temperature within the transformer decreases to a normal level, the thermostat will
reset itself and normal operation will resume. If you are to avoid tripping continually the
thermostat in the transformer, you must reduce the sound level demands into such low
impedances, install auxiliary fan cooling on the amplifier, or both.
For a more detailed description of the operation of the THERMAL PROTECTION LED circuit
and the DC RAIL FUSES, please refer to their respective sections.