HK HK Audio Repair Instruction

Service and

Repair Instruction

for the

HK Audio

Power Amplifier

Projector

Bass

1

1) Terms and Definitions:

- IN: Test Signal Input

- MP: Measuring Points for signal measurements

- R: Resistor to adjust quiescent current

Important: The unit must have an operational fan during testing.

2

2) Basic Measurement Set-up:

Oscilloscope

Function Generator

Input

Ch I

Ch II Trig.Ext.

Amplifier

Probe

Input

Through

Input Impedance at the scope: 10 MO

Trig. Outp.

50O Outp.

Voltmeter

In

NOTE. Turn the input gain controls fully clockwise (viewed from the rear panel)

3

3) Over voltage Protecting Diode:

RRM

Four additional diodes must be mounted seperately on amplifier board to protect the darlington transistors MJ11015 and MJ11016 against over voltage (induced voltage from speaker). Type of diode: BY 500 – 400 or similar

See the following pictures for fitting details.

Protecting Diode BY 500 - 400

Nominal Current: 5 A Repetitive peak

reverse voltage V

: 400 V

T2 (MJ11015) T24

T3 (MJ11016) T25

mounted with soldering lug

4

4) Quiescent Current adjustment:

After replacement of any components, it is vital the output stage quiescent current is adjusted.

A range from 15 to 20 mA is tolerable. To adjust the quiescent current, measure the voltage over the both 0,22O / 5W

resistors for the relevant channel. A voltage of 6,6 mV to 8,8 mV corresponds to the correct current range.

Step 1 Measure the voltage over resistors R4 and R14. Adjust the voltage with trim pot TR1.

Step 2 Measure the voltage over resistors R44 and R45. Adjust the voltage with trim pot TR2.

5

5) Results at the Measurement:

Pre-amplifier Functional Check:

Apply the signal to Input 3; Pins 1 and 2 shorted together Scope to MP1

Note. In step 2, the input amplitude is increased to ensure that the input stage does not clip. In step 3, the input is changed from a sinusoid to a square wave to check the input filters are working correctly.

MP 1: Input Signal: sin; 80 Hz; 1 V

Scope: 5 ms /div; 500 mV= /div

Input Signal: sin; 80 Hz; 5V

Scope: 5 ms /div; 2V= /div

RMS

Input Signal: ; 80 Hz; 0,7 V

RMS

Scope: 5 ms /div; 500 mV= /div

6

Pre-amplifier Functional Check:

Apply the signal to Input 2; Pins 1 and 3 shorted together

Scope to MP1

Note.

In step 2, the input amplitude is increased to ensure that the input stage

does not clip. In step 3, the input is changed from a sinusoid to a square

wave to check the input filters are working correctly.

MP 1: Input Signal: sin; 80 Hz; 1 V

Scope: 5 ms /div; 500 mV= /div

Input Signal: sin; 80 Hz; 5V

Scope: 5 ms /div; 2V= /div

RMS

Input Signal: ; 80 Hz; 0,7 V

RMS

Scope: 5 ms /div; 500 mV= /div

7

Poweramp Limiter Driver:

MP2:

Look at MP3 (Page 9) and MP 6 (Page 12)

8

Power-amplifier Limiter Check:

Apply the signal to the junction of R72 and C31, Scope to MP2, MP3, see the attached diagram.

Note. The GAIN must be turned fully clockwise, and should be reset each time a measurement is taken

MP 2, 3: Signal Input: sin; 1 kHz; 1,13 V

Scope: 500 µs /div; 1V= /div

Explanation to the following picture:

In picture 2 the input sinusoid is shown on channel 2, whilst the output signal is on channel 1. The pulses must occur only at the most negative point on the output waveform.

RMS

9

Power-amplifier Check: Dummy load: 8O + to Plug1; - to Ground

Apply input signal directly to the power amplifier, between R72 and C31, see the attached diagram. Note. In step 2, the input amplitude is increased to ensure that the input stage does not clip. In step 3, the input is changed from a sinusoid to a square wave to check the frequency response of the amplifier.

MP 4: Input Signal: sin; 1 kHz; 0,5V

RMS

Scope: 500 µs /div; 10V= /div

Input Signal: sin; 1 kHz; 0,95V

RMS

Scope: 500 µs /div; 20V= /div

Input Signal: ; 1 kHz; 0,01V

RMS

Scope: 500 µs /div; 500 mV= /div

Attention: Do not run the amplifier for more than 5 seconds whilst making these

tests.

10

Power-amplifier Check: Dummy load: 8O + to Plug3; - to Ground

Apply input signal directly to the power amplifier, between R72 and C31, see the attached diagram. Note. In step 2, the input amplitude is increased to ensure that the input stage does not clip. In step 3, the input is changed from a sinusoid to a square wave to check the frequency response of the amplifier.

MP 5: Input Signal: sin; 1 kHz; 0,5V

RMS

Scope: 500 µs /div; 10V= /div

Input Signal: sin; 1 kHz; 0,95V

RMS

Scope: 500 µs /div; 20V= /div

Input Signal: ; 1 kHz; 0,01V

RMS

Scope: 500 µs /div; 500 mV= /div

Attention: Do not run the amplifier for more than 5 seconds whilst making these

tests.

11

Power-amplifier Limiter Check:

Apply the signal to the junction of R72 and C31, Scope to MP2, MP6, see the attached diagram.

Note. The GAIN must be turned fully clockwise, and should be reset each time a measurement is taken

MP 2, 6: Signal Input: sin; 1 kHz; 1,13 V

Scope: 500 µs /div; 1V= /div

Explanation to the following picture:

In picture 2 the input sinusoid is shown on channel 2, whilst the output signal is on channel 1. The pulses must occur only at the most negative point on the output waveform.

RMS

12

Power-amplifier Check: Dummy load: 8O + to Plug1; - to Ground

Apply input signal directly to the power amplifier, between R72 and C31, see the attached diagram. Note. In step 2, the input amplitude is increased to ensure that the input stage does not clip. In step 3, the input is changed from a sinusoid to a square wave to check the frequency response of the amplifier.

MP 7: Input Signal: sin; 1 kHz; 0,5V

Scope: 500 µs /div; 10V= /div

Input Signal: sin; 1 kHz; 1V

RMS

Scope: 500 µs /div; 20V= /div

RMS

Input Signal: ; 1 kHz; 0,01V

RMS

Scope: 500 µs /div; 500 mV= /div

Attention: Do not run the amplifier for more than 5 seconds whilst making these

tests.

13

Power-amplifier Check: Dummy load: 8O + to Plug3; - to Ground

Apply input signal directly to the power amplifier, between R72 and C31, see the attached diagram. Note. In step 2, the input amplitude is increased to ensure that the input stage does not clip. In step 3, the input is changed from a sinusoid to a square wave to check the frequency response of the amplifier.

MP 8: Input Signal: sin; 1 kHz; 0,5V

Scope: 500 µs /div; 10V= /div

Input Signal: sin; 1 kHz; 1V

RMS

Scope: 500 µs /div; 20V= /div

RMS

Input Signal: ; 1 kHz; 0,01V

RMS

Scope: 500 µs /div; 500 mV= /div

Attention: Do not run the amplifier for more than 5 seconds whilst making these

tests.

14

IN

+15 Vdc

-15 Vdc

MP2

MP1

24 Vdc

-26 Vdc

47 Vdc

-47 Vdc

IN

6,8 Vdc

-1,1 Vdc

-27 Vdc

6,8 Vdc

-1,1 Vdc

1,1 Vdc

R4

R14

R44

R45

MP3

MP5

MP4

1,1 Vdc

35 Vac

-26 Vdc

15 Vdc

-15 Vdc

-27 Vdc

IN+