No Sound In Panasonic TV Repaired
This Panasonic CRT TV came in for repair with the complaint of no sound. Usually no sound symptom can be due to open speaker, broken speaker wire connection, Mute, corrupted EEprom data, missing dc supply to sound output IC, bad sound output IC and etc.
Once the TV cover was removed, I checked on the speakers first and found both of the speakers were good (have Ohms reading).
Next, I checked on the DC supply to the sound output IC-see the photo below:
On the DC supply side to the sound output IC, I measured and got 21.2 VDC but on the other side of the fusible resistor, I got almost zero volt. This usually indicate the resistor already opened circuit.
Since this is a fusible resistor with low ohm (2.2 to 4.7 ohm), this means something had shorted that caused the resistor to open circuit. Chances is very high the sound output IC was shorted.
When I set my meter to Ohms range and checked on the sound output IC vcc pin to ground, I’d got .001 Ohm which means it had a direct short circuit. This is the reason why the fusible resistor was open circuited.
I replaced both the resistor and the sound output IC and powered it on, I was very happy to hear the sound came back again.
Conclusion- Assuming if there is no short circuit and the VCC pin to the sound output IC measured 21 Vdc, then my next step would be to direct replace the sound out out IC and retest. If still no sound then I will reprogram the EEprom IC.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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Albert van Bemmelen
September 18, 2019 at 12:18 am
Straight to the point pro repair where you probably replaced a bad (stereo) TDA amplifier! You didn't mention what type it was and it was neither clear to see from the photo you took. I recently also replaced a TDA 2050 amplifier in a guitar aplifier. It had shorted its pins to the metal housing of the case which immediately destroyed it. Those IC's often are quite difficult to remove from cheap amplifier boards without damaging the copper board pin holes. Cutting the pins one by one first is therefore the best method to remove those defect multi-pin amplifiers.
Devon Wilson.
September 18, 2019 at 1:57 am
Great job. Thanks for sharing. The fusible resistor could have become defective without anything else being damaged. Additionally, the coupling capacitor that couples the audio signal to the speakers could have become defective.
Mark
September 18, 2019 at 8:23 am
Well done Suranga
Phil
September 18, 2019 at 5:08 pm
Great repair job. Thank you for sharing.
Parasuraman S
September 19, 2019 at 1:05 pm
Great job there as usual! Very useful tips too! I really appreciate your next steps at the last! Shows how deeply concerned you are to the new technicians across the world!
Steven
October 14, 2019 at 9:51 pm
Although I enjoy reading about repairing CRT televisions, many people are throwing them away even when they are still operating perfectly: The reason is most people prefer flat screen LCD TVs which typically sell for not much more than the cost of repairing old CRT TVs. I'm not sure it makes much sense to continue publishing articles on repairing old obsolete CRT sets which fewer people want. I would welcome more articles on repairing LCD TVs and their CCFL and LED backlights as well as those with plasma displays.