Marantz SR-12N1G, Service Manual

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1. Check if B voltage is switched to High.
If maximum power can be output, it is OK. IF wave form is clipped and maximum power is not output, it is NG.
2. Check if B voltage is switched to Low.
After adjustment of idling current, if power consumption is within 60W 10W under power on, no signal condition. If it is over
90W, it is NG. It is very possible that B voltage stays High.
Note: Once B voltage is switched to High, it is kept High for 1 minutes. So, power consumption can be over 90W with no signal
condition for 1 minute if B voltage has been switched to High.
B voltage is Low upon turning on the power (initial status) if there is no signal input.
Cooling Fan Check
There is three speeds for the cooling fan, stop, Low Speed and High Speed, depending on the temperature of the heat sink.
Heat sink temperature is monitored with RN62, RN86, thermo sensors for cooling fan. If heat sink temperature becomes higher,
resistance of the sensors also becomes higher. To check the cooling fan, connect test resisters to JN62, JN86 where the thermo
sensors are connected. There are two ways of checking. Remove either sensor and connect the testresister
Fan Speed Test Resister Value Temperature
Stop 1 0 – 220 (0 ) Under 60 ˚C
2 Low Speed 560 – 2.2 k (1.0 k ) 60 – 80 ˚C
3 High Speed 4.7k - (10 k ) Over 80 ˚C
Overheat Protection Check
If monitored temperature of the heat sink goes overheat, microcomputer shuts down the unit to stand-by mode. Heat sink
temperature is monitored with RN47, RN49, thermo sensors for overheat. To check the overheat protection function, connect
test resisters to JN47, JN49 where the thermo sensors are connected.
Function Test Resister Value Temperature
1 Normal 0 – 220 (0 ) Under 110 ˚C
2
Heat Protection
(Stand-by)
4.7k - (10 k ) Over 110 ˚C
If overheat is detected, 2nd pin of J501 is led to GND by a transistor. Normally, it is high impedance (open-collector).
Ω
Ω
Ω
Ω
Ω Ω
Ω Ω
Ω Ω