Safety Precaution - Technics SU-V75 Service Manual

OBRWN =
1.
SAFETY PRECAUTION
. Before servicing, unplug the power cord to prevent an electric shock.
. When replacing parts, use only manufacturer's recommended components for safety.
Check the condition of the power cord. Replace if wear or damage is evident.
. After servicing, be sure to restore the lead dress, insulation barriers, insulation papers, shields, etc.
Before returning the serviced equipment to the customer, be sure to make the following insulation resistance test to
prevent the customer from being exposed to a shock hazard.
NSULATION RESISTANCE TEST
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 jumpered AC plug and each exposed metal cabinet part, such as
screwheads antenna, control shafts, handle brackets, etc. Equipment with antenna terminals should read between 3MQQ
and 5.2MQ. to all exposed parts. (Fig. A) Equipment without antenna terminals should read approximately infinity to
all exposed parts. (Fig. B)
Note: Some exposed parts may be isolated from the chassis by design. These will read infinity.
Antenna
terminal
Exposed Exposed
metal metal
part part
Ohmmeter Ohmmeter
(Fig. A) (Fig. B)
Resistance = 3M2—5.2MQ Resistance = Approx oo
4. If 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.
PROTECTION CIRCUITRY
The protection circuitry may have operated if either of the If this occurs, follow the procedure outlines below:
following conditions is noticed: 1. Turn off the power.
@ No sound is heard when the power is turned on. 2. Determine the cause of the problem and correct it.
@ Sound stops during a performance. 3. Turn on the power once again after one minute.
The function of this circuitry is to prevent circuitry damage
wires are ''shorted'', or if speaker systems with an impedance
Note
When the protection circuitry functions, the unit will not
operate unless the power is first turned off and then on
again.
if, for example, the positive and negative speaker connection
less than the indicated rated impedance of this unit are used.
BEFORE REPAIR
Disconnect AC power, Discharge both Power Supply Capacitors C901 and C902 through a 1022, 5W resistor to ground.
DO NOT SHORT-CIRCUIT DIRECTLY (with a screwdriver blade, for instance), as this may distroy solid state devices.
After repairs are completed, restore power gradually using a variac, to avoid overcurrent.
Current consumption at 120V, 60Hz in NO SIGNAL mode should be 305 ~ 515mA.