Repair Sharp QT-CD130 stereo radio, CD, cassette player 

Date: March 2013

Problem:

The owner brought this 120V boom box to me, it has disc reading error, does not play CD. The radio and cassette play normally.

Diagnosis:

When I plugged it into a 220V to 120V transformer and play the radio, there is a humming noise the increases with the volume. The CD player does not recognize any disc. The first thing I checked is the power supply and found the main electrolytic capacitor with a bulging top and leaking electrolytic fluid on the bottom. In the power supply there is also a heavy transformer like most audio equipment of the 1990s.

 

I suspected that the preview owner brought it over from the U. S. and has been using it on 220V power source. Because the power supply has a traditional transformer, it stepped down the voltage to the main capacitor. So it was designed to step 120V down to less than 20V to the capacitor (20V 4700uf). If it had been used on 220V power source, it may still work for a while because instead of 220V going directly to the capacitor and blow it up right away as seen in other damaged equipment using switching mode power supply, it feeds the capacitor something above 20V like 40V, which could still work for sometime, but will eventually cause the capacitor to fail. Like the saying, it fails gradually, and then suddenly.

Regardless of its cause, the main capacitor has to be replaced.

Repair:

The capacitor was replaced.

Result:

Fortunately, there were no other problems. Once the capacitor is replaced, the CD player works normally. The lens is not an issue in this case. I also discovered the humming noise is caused by my 220V-to-120V power transformer adapter used for voltage conversion that I set on High setting, by switching to Low setting, it went away.

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