Before Repair And Adjustment; Protection Circuitry - Panasonic SA-AK66 Service Manual

1.1. Insulation Resistance Test
1. Unplug the power cord and short the two prongs of the plug with a jumper wire.
2. Turn on the power switch.
3. Measure the resistance value with ohmmeter between the jumper AC plug and each exposed metal cabinet part, such as
screwheads, antenna, control shafts, handle brackets, etc.
Equipment with antenna terminals should read between 3 MQ and 5.2 MQ to all exposed parts*.(Fig.1)
Equipment without antenna terminals should read approximately infinity to all exposed parts.(Fig.2)
*Note: Some exposed parts may be isolated from the chassis by design. These will read infinity.
4. lf the measurement is outside the specified limits, there is a possibility of a shock hazard. The equipment should be repaired
and rechecked before it is returned to the customer.
Antenna
terminal
metal metal
Ohmmeter ' Ohmmeter
Fig. 2
Resistance = Approx co
Resistance = 3MQ —5.2MQ
2 Before Repair and Adjustment
Disconnect AC power, discharge Power Supply Capacitors C571~C574, C579 through a 10Q, 5W resistor to ground.
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 120V, 60 Hz in NO SIGNAL mode should be ~600mA.
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.