3. Protection operation
Explanation of UCOM (U1001) [PROT_1 : pin1, PROT_2 : pin2, PROT_4 : FATAL, pin31, PROT_5 : READY,
pin40, PROT_6 : M_B_DOWN, pin75]
[A] The PROT_1(pin1) is the port to detect the following abnormalities of
the amplifiers circuit
(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 1.5V (DC),[
Q6701, Q6702,
Q6703 or Q6704] will turn on, then the signal from the "PROT_1" will change to "Hi → Lo".
(2) Detects abnormal voltage in the DC offset voltage of the headphone amplifier circuit output.
When the headphone amplifier circuit output exceeds around 1.7V, [
Q9816 or Q9817] turn on and
"
PROT_1" changes from "Hi → Lo".
When "
PROT_1" changes from "Hi → Lo" due to abnormality detected in either (1) or (2), the protection
circuit engages, "
POW_1 : pin72" and "POW_2 : pin73" changes from "Hi → Lo", the power supply relay
[
S8801-S8802] immediately turns off and shuts the unit down.
The STANDBY indicator flickers to inform that an error has occurred.
This protection operation is intended for when a failure occurs in the amplifiers circuit and immediately
turns the power off to avoid the risk of any damage.
To check whether the amplifier is broken, turn off the unit, then wait for about 1 minute and turn it on
again.
This action will deactivate the protection operation.
If the "
PROT_1" remains in the "Lo" abnormal state, which constitutes an abnormality, the unit shuts
down approximately 8 seconds later and the STANDBY indicator starts flickering.
If the protection operation is not deactivated even after the power is turned on again, the amplifiers
circuit may be broken.
[B] The PROT_2 (pin2) is the port to detect abnormalities of the power
supply circuit
(1) Detection of an abnormality in the pre-amplifier power supply circuit.
This port monitors the midpoint voltage b15V and -15V. If the voltage at the connection
point of [
R8151, R8152] exceeds DC ± 1.2V, [Q8151 or Q8152] will turn on to change the signal
from the "
PROT_2" to "Hi → Lo".
(2) Detects abnormalities in the power supply circuit of the TONE circuit.
Monitors TONE circuit power supply midpoint voltage b7V and -7V, and if the [
R2555,
R2556] or [R8151, R8152] connection point voltage exceeds around ± 0.9V (DC), the [Q2553 or
Q2555] turns on and "PROT_2" changes from "Hi → Lo".
(3) Detects abnormalities in the power supply circuit within the POWER PCB.
① Detects over-voltage (+9V or more) in +3.3VD of the DIGITAL circuit power supply, then [
Q8551]
turns on and "
PROT_2" changes from "Hi → Lo".
② Monitors DIGITAL circuit power supply midpoint voltage b12V and -12V, and if the
[
R8551, R8552] connection point voltage exceeds 0.9V, [Q8552 or Q8553] turns on and "PROT_2"
changes from "
Hi → Lo".
③ Detects short circuits in +24V or +8V of the relay power supply, then [
Q8554] turns on and
"
PROT_2" changes from "Hi → Lo".
(4) Detects abnormalities in the OLED power supply circuit
① Detects short circuits in +17V of the OLED power supply, then [
Q1024] turns on and "PROT_2"
changes from "
Hi → Lo".
② Detects over-voltage in +17V of the OLED power supply, then [
Q1026] turns on and "PROT_2"
changes from "
Hi → Lo".
When the abnormality mentioned in (1) or (4) is detected, "
POW_1 : pin72" and "POW_2 : pin73"
change from "
Hi → Lo" and power relay [S8801, S8802] immediately turns off and shuts down.
The STANDBY indicator flickers to inform that an error has occurred.
This protection operation is intended for when a breakdown of the power supply circuit occurs and im-
mediately shuts off the power in order to avoid the risk of damage.
To check whether the power supply circuit is broken, turn off the unit, then wait for about 1 minute and
turn it on again.
This action will deactivate the protection operation.
If the "
PROT_2" remains in the "Lo" abnormal state, which constitutes an abnormality, the unit shuts
down approximately 5 seconds later and the STANDBY indicator starts flickering.
If the protection operation is not deactivated even after the power is turned on again, the power supply
circuit may be broken.
Before Servicing
This Unit
Electrical
Mechanical
Repair Information
Updating
51
