Marantz PM8005 Service Manual page 17

[B] The PROT_2 (pin7) is the port to detect abnormalities of the power supply circuit.
1. Detection of an abnormality in the power amp power supply circuit.
This port monitors the midpoint voltage of the power amp power supply between +49V and -49V. If the voltage at the
connection point of R8001 and R8002 exceeds DC ±1.2V, Q9003 or Q9004 will turn on to change the signal from the
PROT_2 (pin7) to "Lo" from "Hi".
2. Detection of an abnormality in the preamp power supply circuit.
Q9001 and Q9002 monitors the midpoint voltage between +28V and -28V. If the voltage at the connection point of
R8109 and R8110 exceeds DC ±0.9V, Q9001 or Q9002 will turn on to change the signal from the PROT_2 (pin7) to
"Lo" from "Hi".
3. Detection of an abnormality in the function relay power supply circuit.
If the +24VL of the relay power supply receives an electric current of over 80mA, Q8302 and Q8303 will turn on to
change the signal from the PROT_2 (pin7) to "Lo" from "Hi".
If any of the above three abnormalities is detected, the signal from the P_ON (pin15) terminal will be changed to "Lo" from
"Hi", the power relay S8051 will be turned off and the unit will be shut down. Then, the STANDBY indicator flickers and
indicates that an abnormality has occurred.
This protection operation is intended for a breakdown of the AMP circuit or the power supply circuit and immediately shuts
off the power in order to avoid the risk of damage.
To check if the amp circuit or the power supply circuit is broken, switch off the power and then switch it on again one
minute later. This action will deactivate the protection operation.
If the RPOT_2 (pin7) remains "Lo" after the power is switched on again, the unit will be shut down again three seconds
later with the STANDBY indicator flickering.
If the unit is powered on again and yet cannot get the protection operation deactivated, the amp circuit or the power supply
circuit may be broken.
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