Job Number

0010-08

Equipment type

Audio stereo receiver Amplifier

Maker + Model #

YAMAHA  R-300

Made in

Japan

Comments

1)      Was bought second hand, very old judging from the rusty back panel, nice tuning mechanism.

2)      The cost of the broken IC was very expensive for the owner and decided not to fix the equipment.

BAD

1

No Sound Output

2

No Relay ‘click’ after start up.

GOOD

1

Tuner back display and tuning pointer lights up

2

No part of the circuit produces excessive heat

Repair summary

BROKEN AF POWER AMP IC STK2030 II

Full repair description and observations

1

First suspicion fell on the power supply. The 2 reservoir capacitors (connected in series) did supply the +41V and –41V to the amplification circuit.

2

The amplification system mainly consisted of two large ICs :

1)       STK3042 a Voltage amplifier and

2)       STK2030II an Audio Power Amplifier.

These were symmetrical ICs, and the pins from the centre to the left were identical to the pins from the centre to the right.

3

The voltage at the pins of the two ICs were taken and compared. The voltages of the two sides (channels) of each IC were not equal, as shown below. The pinouts given below are theoretical assumption from the datasheets found on the internet. (The ICs are Sanyo).

STK 3042 (Voltage Amplifier)

STK 2030 (AF Power Amplifier)

Pin

Function

Voltages

Pin

Function

Voltages

(a)

(b)

(c)

(a)

(b)

(c)

1

Input

-43mV

-50mV

0

1

L:      Input (+)   

- 9.2 V

42 V

0

2

Input

-43mV

-50mV

0

2

+ Vcc

41 V

42 V

42 V

3

Output ?

40 V

41 V

0

3

Output (+)

-40mV

-50mV

0

4

Output ?

40 V

41 V

0

4

/

/

/

/

5

Output ?

- 11.2V

- 42 V

0

5

Output (-)

-40mV

-50mV

0

6

Output ?

- 9.2V

42 V

0

6

- Vcc

- 42 V

- 42 V

- 42 V

7

Vcc -

- 41 V

- 42 V

- 42V

7

Input (-)

- 11.2V

- 42 V

0

8

GND

0

0

0

8

/

/

/

/

9

Vcc +

+41 V

42 V

42 V

9

/

/

/

/

10

Output ?

7.5V

42 V

0

10

R:     Input (+)   

5.1 V

- 42 V

0

11

Output ?

5.1V

- 42 V

0

11

+ Vcc

- 42 V

- 43 V

- 42 V

12

Output ?

41 V

41 V

0

12

Output (+)

16 V

- 50mV

0

13

Output ?

40 V

41 V

0

13

/

/

/

/

14

Input

16 V

-50 mV

0

14

Output (-)

16 V

-50mV

0

15

Input

7 V

-50 mV

0

15

- Vcc

41.5 V

42V

42 V

16

Input (-)

7 V

42V

0

(a) Both ICs in place

(b) STK2030 removed

(c) Both ICs removed

4

It was noted that on pin 1 and 2 of the STK3042 there was no voltage (0.1V), while on the equivalent pins of the other channel (pins 14 and 15) there was 15V and 7V. These voltages were routed to/from pins 3 and 5 (also 14 and 12) of the STK 2030.

5

Test points on the PCB were labelled 15V and –15V, of which the –15V were found, while the +15V were not found. It is assumed that these are the voltages to be found under operating conditions.

6

The source of the +15 and –15V was not determined, and hence could not solve the problem. It is not excluded that these voltages come directly from any of the STK ICs and hence the lack of these voltages indicates that any of the ICs is broken.

7

On desoldering the STK2030 Power amp, the relay did click, and not bot voltages at the input became 0.1V. This is an indication that the STK2030 is broken, but not prove is found to confirm this, especially when checking all pins with the diode test, the results were symmetrical but some were not as theoretically demonstrated on the data sheet equivalent circuit. The significant results (those which gave a reading) are shown below while the full results are shown in Table 1 (under ‘other measurements’)

Pin – Pin Diode Test

Fow (L)

Fow (R)

Rev (L)

Rev (R)

Pin – Pin Diode Test

Fow (L)

Fow (R)

Rev (L)

Rev (R)

Pin 1 – 2

0.6

0.6

/

/

Pin 3 – 4

/

/

/

/

3

1.0

1.0

/

/

5

/

/

/

/

4

/

/

/

/

6

/

/

1.1

1.1

5

/

/

/

/

7

/

/

/

/

6

/

/

1.7

1.7

7

1.2

1.1

1.4

1.4

Pin 4 – 5

/

/

/

/

6

/

/

/

/

7

/

/

/

/

Pin 2 – 3

/

/

/

/

4

/

/

/

/

Pin 5 - 6

/

/

/

/

5

/

/

/

/

 7

/

/

/

/

6

/

/

1.1

1.1

7

/

/

1.7

1.7

Pin 6 – 7

0.6

0.6

/

/

8

The Voltage amp (STK2030) was also desoldered and the Diode test was performed between its pins to note any differences.  Pin 7 and the complementary pin 9 showed some differences to some pins, but this might be due the fact that pin 7 takes a positive VCC while pin 9 takes a negative VCC voltage, and hence the internal circuit is different between pin 7 and 9.

Pin – Pin Diode Test

Result (Forw)

Pin – Pin Diode Test

Result (Forw

Pin – Pin Diode Test

Result (Forw

Pin – Pin Diode Test

Result (Forw

Pin 1 – 3

1.3

Pin 15 – 13

1.3

Pin 9 – 12

0.6

Pin 9  - 3

0.6

Pin  1 – 4

0.7

Pin 15 – 12

0.7

Pin 9 – 13

0.6

Pin 9 – 4

0.6

Pin 2 – 3

0.7

Pin 14 – 13

0.7

Pin 10 – 12

1.3

Pin  6 – 4

1.4

Pin 6 – 9

1.1

Pin 10 – 9

1.1

Pin 10 –13

1.3

Pin 6 – 3

1.4

Pin 6 – 12

1.5

Pin 10 – 4

1.5

Pin 12 – 13

0.6

Pin 4 – 3

0.6

Pin 6 – 13

1.5

Pin 10 – 3

1.5

Note the symmetry of results between column 2 – 4 and 6 – 8.

9

At this point it was obvious that one of the IC was broken, and to confirm things out, many of the components around the IC were checked and found to be OK. These included many resistors, 3 transistors and about 4 capacitors.

10

The STK3042 was mounted back in place, and one channel of the STK2030 AF Amp was also mounted. The channel mounted was the ‘good’ one, were the 15V were found. On powering up, the relay did not clicked, indicating that there is a fault!

11

Still puzzled, this channel was desoldered again, while the channel which it was suspected to be faulty (were there was no 15V found) was soldered back. The set was powered up, and with a surprise, not only that the relay click was  obtained, but the sound output was given out (via the headphone jack). Thus the faulty channel is that were the 15V are present while the good channel were there was -0.1V.

12

The voltages of the STK3042 (fully connected to PCB) and those of the STK2030 (with the faulty channel not connected) were measured and the results obtained are as follows:

13

STK 2030 AF Power Amp

(faulty channel pins 10-16 disconnected)

STK3042 Voltage amplifier – fully connected

(faulty side pins 9-15)

Faulty

Good

Faulty

Good

Pin

Voltage

Pin

Voltage

Function

Pin

Voltage

Pin

Voltage

Function

16

40V

1

-2.8V

Input

15

-70mV

1

-40mV

Input

15

41V

2

42V

VCC +

14

-70mV

2

-40mV

Input

14

-135mV

3

7mV

Output

13

40V

3

+40V

?

13

/

4

/

/

12

40V

4

+40V

?

12

-135mV

5

6mV

Output

11

-41V

5

-5.3V

Output

11

-42V

6

-42V

VCC -

10

40V

6

-2.8V

Output

10

-42V

7

-5.3V

Input

9

+41V

7

-41V

VCC

14

I resoldered the 3042 in place and began a series of tests to check whether one of the channels is not operating due to a faulty channel in the Power amp (STK2030), or a faulty output from the Voltage amplifier (STK3042).  The test s are performed as shown below:

Test applied on 2030

Relay

Click

Sound

o/p

Comments

Voltage readings (2030)

Pin 10 (i/p)

Pin 16 (i/p)

Pin 12

(o/p)

Pin 14

(o/p)

1

Exchange input  from working channel to faulty channel.

No

No

If the sound was produced, then the 2030 channels are both OK,  but now it means that one channel of the 2030 is broken

/

/

16V

16V

2

Desolder input and output of faulty channel

Yes

No

The problem is with the signal routing (i/p or o/p)

/

/

16V*

16V*

3

Desolder output of faulty channel (input is  connected)

Yes

No

The problem is with the output of the faulty channel. It is giving of a 16V which may be a means of protection to switch off the relay and prevent further damage to the speakers

5V

7V

16V*

16V*

4

Connect output from 3042 ‘faulty side’ to good side of the 2030

Yes

Yes

Confirmed. 3042 working perfectly, one channel of the 2030 is broken, the other  one is OK

-5V

-8V

0.5V

0.5V

5

Connect output from one side of 3042 to inputs of both sides of 2030.

No

No

The faulty channel produced those 16V and turned off the relay.

16V

16V

*      The voltages are measured from the desoldered pins of the IC. Since these are not connected to the track, the  ………..relay does not sense the presence of the16V and so it operates

n.b.  The voltages measured are volume dependent. If the volume is increased, the voltage varies accordingly.

15

The inputs and outputs of the faulty channel of the 2030 was desoldered so that the amplifier will operate at least on one channel (one speaker).

16

Finally the knobs were serviced with contact spray for better operation

Precautions, fouls and advises

1

1

The relay is a component with at least 6 pins. 2 of these are connected to a solenoid coil. The other 2 pairs are pins of 2 switch contacts. When DC voltage is passed through the coil, the core gets magnetised and  pulls an iron lever, which in turn cause the 2 switches to close. The resistance of the coil was 500 Ohms, and during operation, one was terminal was 23V, while the other was 150mV. When both sides were 23V (no voltage drop) the relay did not operate (close).  

2

Table 1: Diode test pin combination for the IC STK2030 (Voltage amplifier)

Pin – Pin Diode Test

Fow

Rev

Pin – Pin Diode Test

Fow

Rev

Pin 1 – 2

/

/

Pin 6 – 7

/

/

3

1.25

/

8

/

/

4

0.72

/

9

1.1

/

5-15

/

/

10

/

/

11

/

/

Pin 2 – 3

0.71

/

12

1.5

/

4-15

/

/

13

1.5

/

14-15

/

/

Pin 3 – 4

/

0.6

5

/

/

Pin 7 - *

/

/

6

/

1.35

7

/

/

Pin 8 - *

/

/

8

/

/

9

/

0.6

Pin 9 – 10

/

1.1

10

/

1.51

11

/

/

11-15

/

/

12

0.62

/

13

0.6

/

Pin 4 – 5

/

/

14-15

/

/

6

/

1.35

7

/

/

Pin 10 – 11

/

/

8

/

/

12

1.25

/

9

/

0.6

13

1.23

/

10

/

1.5

14-15

/

/

11-15

/

/

Pin 11 - *

/

/

Pin 5 - *

/

/

Pin 12 – 13

0.58

/

14

/

/

15

/

0.7

Pin 14 – 15

/

/

Pin 13 – 14

0.74

15

1.27

3

Included below are the datasheets for the STK3042 and the STK2230 family (2030 not included but similar circuits are demonstrated). Obtained from Yahoo search (site = laboratories of Georgia). Manufacturer is SANYO.