4
2.1.2.
Leakage Current Hot Check
1. Plug the AC cord directly into the AC outlet. Do not use an isolation transformer for this check.
2. Connect a 1.5k
, 10 watts resistor, in parallel with a 0.15
F capacitors, between each exposed metallic part on the set and a
good earth ground such as a water pipe, as shown in Figure 1-1.
3. Use an AC voltmeter, with 1000 ohms/volt or more sensitivity, to measure the potential across the resistor.
4. Check each exposed metallic part, and measure the voltage at each point.
5. Reverse the AC plug in the AC outlet and repeat each of the above measurements.
6. The potential at any point should not exceed 0.75 volts RMS. A leakage current tester (Simpson Model 229 or equivalent)
may be used to make the hot checks, leakage current must not exceed 1/2 milliamp. In case a measurement is outside of the
limits specified, there is a possibility of a shock hazard, and the equipment should be repaired and rechecked before it is
returned to the customer.
Figure 1-1
2.2.
Before Repair and Adjustment
Disconnect AC power to discharge AC Capacitors (C1003, C1004, C1005, C1007, C1008, C1009, C1010) through a 10
, 10 W
resistor to ground.
Caution:
DO NOT SHORT-CIRCUIT DIRECTLY (with a screwdriver blade, for instance), as this may destroy solid state devices.
After repairs are completed, restore power gradually using a variac to avoid overcurrent.
Current consumption at AC 220~240 V, 50/60 Hz in Power ON, FM Tuner at volume minimal mode should be ~ 750 mA.
2.3.
Protection Circuitry
The protection circuitry may have operated if either of the following conditions are noticed:
• No sound is heard when the power is turned on.
• Sound stops during a performance.
The function of this circuitry is to prevent circuitry damage if, for example, the positive and negative speaker connection wires are
“shorted”, or if speaker systems with an impedance less than the indicated rated impedance of the amplifier are used.
If this occurs, follow the procedure outlines below:
1. Turn off the power.
2. Determine the cause of the problem and correct it.
3. Turn on the power once again after one minute.
Note:
When the protection circuitry functions, the unit will not operate unless the power is first turned off and then on again.
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