Job Number

0010-04

Equipment type

Car Stereo Radio Cassette

Maker + Model #

MATSUI   3110Xqi

Made in

Korea

Comments

BAD

1

No sound output from left channel  (blue + green connection)

2

Cassette non operational – no rotation of the pinch roller, etc

3

Over heating of the back panel (location of the power audio transistors)

GOOD

1

Right channel sound OK

2

Powers up, etc

3

Cassette motor functions well (can be heard operating)

Repair summary

1)     FAULTY AUDIO POWER AMPLIFIER

2)     MOTOR CHAIN OUT OF POSITION

Full repair description and observations

Fault A:  No  sound  at  left  channel

1

When the item was opened, it was noted that one of the power amps was very, very hot.

2

The voltages at the pins of the 2 ICs were compared and the results are shown in Table 1 (below). There were different readings and the faulty IC had mysterious same voltage levels between 2 pairs of adjacent pins (short circuit -> heat dissipation ?)

3

The suspected and the good power amps were desoldered, removed from position and checked for their internal resistance between the pins. The results are shown in table 2 (below). It was concluded that the IC was faulty and bought a new one.

4

The audio amp was a Single in Line, 12-pin IC – LA 4445. Pinout is shown in table 3 (below)

5

I also checked the voltages at the chip track slots (were the chip was soldered) to ensure that the IC was not burnt out due to an abnormal high voltage or short circuit at any pins. Both sides had a 12V supply at pin 9 and the rest had a couple of milliVolts

6

I replaced the faulty IC, and added new heat transfer material, powered up and the faulty left channel played successfully.

Fault B:  Cassette non functioning, but motor sounds running

1

This is atypical case of a slipped motor/pulley chain, so the cassette section was disassembled out.

2

The chain was in fact out of position, and hence was loaded back into place.

3

When the cassette was assembled back, and tested with a tape, it did a strange grinding noise and also jumbled the tape magnetic strip.

4

On inspection of this problem, it was noted that the rotators were moving in opposite direction, and concluded that this was due to placing the motor/pulley chain in a wrong position.

5

Instead of disassembling the cassette again, the dc motor voltage supply polarity was invades (also inverting the parallel capacitor) by ex-changing the voltage supply +ground wires

6

On testing, the cassette operating excellently!

Precautions, fouls and advises

1

While desoldering the IC, excessive heat caused some track slots to break.

2

The desoldering wick was much better from the suction pump for desoldering IC pins

3

Disassembling and assembling of the cassette was a very tricky job to do, and can easily lead to confusion when assembling back. The best thing is to note every section of the cassette how it is positioned, and write the observations on paper.

4

Loading back the motor/pulley chain is not just a job of putting it in the grooves. One should study the direction of rotation of the motor in respective with the direction of the playback of the tape, in order to fit the chain as originally was. In this case the chain was placed wrong!

5

If the playback results in grinding clicking sound, and plastic slips sound, it is very probable that the rotation is operating in the opposite direction. In this case, practice showed that inverting the motor polarity would effectively solve the problem!

6

During assembling back, the eject cassette push lever was not in place, and the eject system was non-operative. Excessive pressure broke a small part of this plastic mechanical part, but fortunately it was not critical. This should extend from the backside of the cassette, (approx. parallel to the side) to about 45 degrees inwards, near the first cassette roller.

7

Always note the impedance output of the amplifiers, in order to test the sound with speakers of the right impedance. Never use speakers of lower impedance from that of the amps output

##

Spare part item description

Shop / source

Price / LM

01

LA4445  IC (Audio power amp, SIL)

Mapp electronix

LM1.16

Approx. working time

4

hours

Fault Difficulty Level

4

out of 10

Total price for parts

LM

1.20

Final repairing price

LM

2.00

1

See tables below

Table 1: Comparison of the voltage at the pins of the two Audio Power Amps.

Pin

Good IC

Suspected IC

Pin function

Observation

1

1.2V

0.7V

RC chain to left ground

OK

2

16mV

315mV

Right input

OK

3

4mV

10mV

Ground

OK

4

11V

2V

C to Ground

2V Low ?

5

3mV

9mV

Left input

OK

6

1.2V

1.6V

RC chain to right ground

OK

7

10.4V

2.7V

C to out left

2.7V Low ?

8

5.9V

2.7V

Out left           

Short circuit with pin 7 ?

9

11.9V

11.7V

Vcc

OK

10

5.9V

2.3V

Out right

2.3V Low ?

11

10V

2.3V

C to out right

Short circuit with pin 10 ?

12

0V

0V

Ground

OK

Table 2: Comparison of the internal resistance between pins of a good & faulty LA4445 (Audio Power Amp.)

Test pins

Good

Faulty

Test pins

Good

Faulty

Test pins

Good

Faulty

Pin  12 – 11

10k

Inf

Pin  10 – 9

1k

600

Pin  7 – 6

30k

Inf

10

580

510

8

1k

15k

5

4M

Inf

9

1k

150

7

10k

Inf

4

11k

Inf

8

580

15k

6

20k

28k

3

4M

Inf

7

10k

Inf

5

4M

4M

2

4M

Inf

6

20k

27k

4

1.6k

1k

1

30k

Inf

5

4M

4M

3

4M

4M

4

1.6k

650

2

4M

4M

Pin  6 –5

4M

3M

3

4M

4M

1

20k

2M

4

22k

22k

2

4M

4M

3

4M

4M

1

20k

2M

Pin  9 – 8

1k

154

2

4M

4M

7

10k

Inf

1

43k

2.2M

Pin  11 – 10

9k

Inf

6

20k

27k

9

10k

Inf

5

4M

4M

Pin  5 – 4

Inf

1.3M

8

10k

Inf

4

500

500

3

31k

5M

7

20k

Inf

3

4M

4M

2

63k

5M

6

30k

Inf

2

4M

4M

1

Inf

3M

5

4M

Inf

1

20k

2M

4

11k

Inf

Pin  4 –3

4M

4M

3

4M

Inf

Pin  8 – 7

9k

Inf

2

4M

4M

2

4M

Inf

6

19k

31k

1

22k

2M

1

29k

Inf

5

4M

4M

4

1.6k

600

Pin  3 – 2

30k

28k

Grey = faulty

3

4M

4M

1

Inf

10M

2

4M

4M

Pins 1,7,11

1

20k

2M

Pin  2 - 1

Inf

10M

Open circuit

Table 3: Specifications and Pinouts of the LA4445 Audio Power Amp IC.

LA4445 Power amplifier

Power Output:  2 x 5.5 W      Impedance: 2 x 3 ohm

P(out) (U = 16V) 5.5 W

U dc. Min = 8V

U dc. Max = 24V

U in.     = 0.25V

Gain      = 48db

f         = 30Hz-20KHz

Noise (P out=5W) = 64db

Pinouts:

pin 1 - RC chain to ground ("Right" cannel)

pin 2 - Input "Right"

pin 3 - Ground

pin 4  - C to Ground

pin 5 - Input "Left"

pin 6 - RC chain to ground ("Left" cannel)

pin 7 - C to out ("Left" cannel)

pin 8 - Out ("Left" cannel)

pin 9 - U dc (VCC)

pin 10 - Out ("Right" cannel)

pin 11 - C to out ("Right" cannel)

pin 12 - Ground

C – capacitor   ---||---

                         ___

RC chain        ---||---| R |---