Harman kardon hk 1680 service manual

Page 2

l hk1680

PRECAUTIONS -' .~ a. V , ,. ,"

1.

Always disconnect the chassis from power line when soldering. Turning the power switch OFF Is not enough.

Power line leakage passing through the heating element may destroy the transistors.

2. Never attempt to do any work on the transistor amplifiers without first disconnecting the AC line cord and
. waiting until 'the power supply filter capacitors have discharged. ' ., - .
3. Replacement for output and driver transistors, if necessary, must be made from the same beta group as the
_ original type

4. If one output transistor burns out (open or short) always remove all the output transistors in that channel and
check the bias adjustment, the control and other parts in the network with an ohmmeter before inserting a new
transistor. All transistors in one channel will be destroyed if the base biasing circuit is open on the emitter end.

5. When mounting a replacement power transistor, be sure that the bottom of the flange. the mica insulators and
the surface of the heat sink are free of foreign matter, for they may cause transistor failure.

6. Silicon grease must be applied between the transistor and the mica insulator, and between the mica insulator and
the heat sink for better heat conduction.

7. Fuses must be replaced with size and type indicated. Use of other types can expose components to destructive

current levels.

ALIGNMENT PROCEDURES

AM ALIGNMENT

Instruments: '1. AM Signal Generator modulated with 4OOHz at 30%. L V , t
2. Oscilloscope "
3. AC V.T.V.M,
4. DC Voltmeter -
Notes: 1 . Set function selector switch to AM position
2. Connect signal source to a loop placed to radiate signals into AM antenna loop stick (L251)
3. Set odd/even selector switch to EVEN position.

Step I Signal Source Connect Output Meter To 3:32; D'Splay Adjust Adjust For
Maximum output on
VTVM and oscilloscope to T251, VTVM and at the same
450kHZ TP1 and ground 1610kHz T252 time clean wave form on
oscilloscope
VTVM and oscilloscope to
450kHz TP2 and ground 1610kHz T253 Same as above
7 Dc met ° 3 3"" 530kHz L252 1.62v on DC voltmeter
ground
- Same as above 1610kHz TC252 22.5V on DC voltmeter
5 600kHz VTVM to Tape 1 Out jack 600kHz L251 \fficmum 9 °
6 1400kHz Same as above 1400kHz TC251 Same as above
Repeat steps 5 and 6 for optimum sensitivity.
1000kHz Oscilloscope to Tape 1 Out Clean wave form on
8 40dB/m(100p V/m) jack 1000 VR251 oscilloscope