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General information

 

Job Number

 

0201-38

 

 

 

 

Equipment type

 

Car Stereo (Radio+Cassette)

 

 

 

Maker + Model #

 

Denver Sparkomatic

 

 

 

Made in

 

Korea

 

 

 

 

Comments

 

Could not find fault, and continued again to work on it 3 months later. After fixing it, Louis said that I can keep the radio since his friend is not in Malta at the moment.

 

 

 

Symptoms observed

 

 

BAD

1

All bands of radio does not play

 

 

 

 

 

 

GOOD

1

Powers up

 

 

 

 

2

Cassette functions well, and good sound is produced

 

 

Repair notes

 

Full repair description and observations

 

1

Initially the radio band select swtiches were investigated for a probable jamming, dry joint, or mechanical fault, but there was nothing obvious as such.

 

 

2

The circuit was very tedious and the amp IC (SP 800 by SGS) could not be found on the internet for a datasheet. Various attempts and guess work was done to find a faulty component but everything seemed to be good

 

 

 

3

After several weeks, I decided to buy the 4 main IC that the tuner had (except the amp IC) perhaps one of these went open. They were purchased from UK (telepart) and the price came to GBP11.03. I replaced and soldered the FM tuning IC, but there was no success. Before replacing the other IC I decided to give a lokk at their datasheets. One of the IC was a noise reduction, and the other was a pre-amp for the cassette playback.

 

 

4

The power supply for the FM tuning IC, (just replaced) was found on the datasheet that it should be 12V, but on the circuit I had 0.1V. I followed the power supply track on the circuit and finally I found a dry joint at resistor in series with the Vcc in of the IC. 

 

 

5

When the dry joint was fixed, all bands of the radio became operative and hence the fault was fixed.

 

 

6

Finally a general service was given, which included replacing faulty light bulbs, cleaning the head and pinch roller and greasing mechanism of the cassette unt, cleaning user potentiometers (eg volume) and switches.

 

 

Repair summary

OPEN CIRCUIT AT VCC OF THE TUNER Ics DUE TO A DRY JOINT

 

 

Precautions, fouls and advises

 

1

Before buying Ics as an action of guess due to a clueless fault, check the function of the IC from the internet. For example in this case, the noise canceller IC could have been avoided.

 

 

 

 

 

Other measurements and technical comments

 

1

When the cassette is on operation the voltage is given to the pre amp, while when the radio is used, the preamp is switched off. Hence the Pre-Amp is used only for the playback of cassette.

 

 

2

The following IC.s were present in the circuit:

 

LA 1130    - AM tuning IC

LA 1140    - FM Tuning IC

LA 2110    - Noise canceller

TA 7325P – Audio Pre-Amplifier

 LA 3376   - ??  

SP800      -  Audio Power Amplifier

 

 

 

 




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