Marantz PM8005 - Protection Mode

2. PROTECTION MODE
Explanation of microprocessor
(U1001)
[PROT_1 (pin6) and PROT_2 (pin7)].
[A] The PROT_1(pin6) is the port to detect the following abnormalities of the Power AMP
1. Detection of an abnormality in the DC offset voltage from the Speaker Output terminal.
If the voltage from the Speaker Output terminal exceeds approximately 1.2V (DC),
Q9507
or
Q9508
will turn on and
the signal from the PROT_1 terminal will change to
"Lo"
from
"Hi"
.
2. Detection of an abnormal current from the power transistors (
Q7011
,
Q7013
,
Q7012
,
Q7014
).
If an electric current of over 7A ows in
Q7011
or
Q7013
,
Q9503
,
Q9505
and
Q9509
turn on, and the signal from the
PROT_1 terminal will change to
"Lo"
from
"Hi"
.
If an electric current of over 7A ows in
Q7012
or
Q7014
,
Q9504
,
Q9506
and
Q9509
turn on, and the signal from the
PROT_1 terminal will change to
"Lo"
from
"Hi"
.
3. Detection of an abnormal temperature of the Heat Sink.
If the temperature of the Heat Sink exceeds approximately +110 degrees C, the posistor (
Z9501
or
Z9502
) will turn on
Q9501
or
Q9502
and the signal from the PROT_1 terminal will change to
"Lo"
from
"Hi"
.
If any of the above three abnormalities is detected, the signal from the PROT_1 terminal will change to
"Lo"
from
"Hi"
,
and the protection circuit will be activated, the signal from the SPK_OUT (pin10) changing to
"Lo"
from
"Hi"
and the
speaker relays
S7501
,
S7502
and
S7503
immediately turned off.
What this protection operation results in after this depends on how long the signal from the PROT_1 has to remain
"Lo"
.
• If the PROT_1 (pin6) recovers to
"Hi"
within as short a period of time as one second or less.
The MUTE indicator starts ickering, thereby indicates that the protection circuit has come into operation and
automatically turns down the volume. The protection circuit is deactivated after approximately 15 seconds, so that
readjusting the volume will allow normal use of the unit again. This protection operation is intended for the situation
wherein the user has misused the unit temporarily and automatically resets the unit while the amp circuit is functioning
properly.
• If the PROT_1 (pin6) remains
"Lo"
for more than one second.
The amp will be powered off by the P_ON (pin15) changing to
"Hi"
from
"Lo"
and and Power relay
S8501
turned off
Then, the STANDBY indicator ickers, thereby indicating that an error has occurred. This protection operation
is intended for a failure in the amp circuit and immediately turns the power off to avoid the risk of any damage.
Depending on how the user is handling the unit, this operation may be performed no matter if the amp is functioning
properly.
To check if the amp is in order, switch off the unit and switch it on again one minute later. This action will deactivate
the protection operation. If the PROT_1 (pin6) remains
"Lo"
, which constitutes an abnormality, the unit shuts down
approximately 3 seconds later and the STANDBY indicator starts ickering.
If the protection operation will not be deactivated after the power is turned on again, the amp circuit may be broken.
16