Job Number

0102-19

Equipment type

Stereo Midi Sytem

Maker + Model #

Pioneer

Made in

Japan

Comments

BAD

1

The system powers up for 3 secs and then it shuts down.

GOOD

1

A blinking 0:00 led remains after shut down.

Full repair description and observations

1

.First the system was cleaned from dust by means of a vacuum cleaner and paint brush.

2

. Initially the power supply was being tested. Following the tracks of the a.c. it was noted that from the output of the primary transformer, there were 2 relays. During the initial 3 seconds there was voltage on the relays, but than when the system shuts down, the relay opens and a.c could be further processed to the power supply. The relays are in PROTECTION MODE

3

On examining the circuitry, 4 heat-sinked transistors were suspicious of having brown – burned like substance beside. However on further inspection this was dried sticky substance which served to hold firmly the heat sinks

4

From experience the suspect fell immediately on the power amplifier – a large Sanyo ic of 18 pins. This was an STK4141 II STEREO AMPLIFIER. Its pins were de-soldered and the supplied voltages were measured. 2 pairs of +37.5V and –37.5V were found on pins:

11,12 (+37.5V) and 9, 14 (-37.5V)  Therefore, the supply voltages are good

5

The pins were checked for possible shorts, and a short circuit was found between pins 13 and 14. On examining the datasheet pins 13 and 14 are supply voltage and audio output, which never they could be common (short).

6

The IC was replaced and the system powered up and an excellent sound output was given

7

Finally the counter belts was found to be broken. It was replace (and it was really a hard job to disassemble the mechanism around) and the counter worked fine.

8

The tape heads and pinchrollers were cleaned with absolute alcohol

9

Finally the system was closed back and gave a nice cleaning of the front panel, sliders, buttons etc.

Repair summary

AUDIO STEREO AMPLIFIER IC FAULTY (Short circuit)

Precautions, fouls and advises

1

To put the rev counter belt in the inner pulley, most of the tape deck section had to be removed. This involved unplugging about 7 plug in ribbon cables. Each was marked accordingly.

These cables had a very nasty lock mechanism. Excessive pressure with the screwdriver during the locking back of one cable caused the lock cover to break. This could have been avoided with little care. Anyway, the cable was inserted in the socket and was hold in place using the evo-stick.