sharp with tda9381 there is no picture, normal voice

One of the faults found in Sharp televisions using the TDA9381 IC is a dark screen with normal sound and OSD. In this condition, the television appears to operate normally, but the picture does not appear. The diagnosis should focus on the video signal and the ABL circuit.

Symptoms of Sharp TV TDA9381 No Picture

The symptoms found in this case are:

The television turns on and produces normal sound.
The screen remains dark or has no visible picture.
The OSD (On-Screen Display) can still appear.
There is no picture when using the AV input.

Because the OSD is still visible, the fault is not necessarily caused by a completely inactive horizontal or vertical deflection circuit. The ABL and video processing circuits should also be checked. For related symptoms, see Sharp TV fault analysis.

Checking the ABL Circuit

ABL stands for Automatic Brightness Limiter. This circuit supplies feedback related to the CRT beam current. If the ABL voltage is missing or abnormal, the television may exhibit picture problems.

On the Sharp TDA9381 chassis examined in this case, the ABCL/ABL pin voltage was checked. The expected voltage was approximately 3 V, but no voltage was measured at the pin.

The flyback transformer ABL output was then checked at pin 1. The meter needle deviated toward the negative direction, whereas the normal measurement in this case was approximately 4 V. This indicated that the ABL circuit required further inspection.

Checking Resistor R604 and R605

Further inspection found that resistor R604 was open. R605 was also checked because it receives its supply voltage from B+. An open resistor in this section can interrupt the ABL voltage path and cause abnormal operation.

Check R604 for continuity and verify the voltage path through R605 and the surrounding components. Confirm the resistor values against the circuit diagram for the exact chassis before replacing any component.

Distinguishing ABL Faults from Other Picture Problems

A dark screen with no OSD is different from a condition where the OSD appears normally. If the OSD is visible but the video picture is missing, inspect the video processing path as well as the ABL circuit.

For other Sharp protection symptoms, refer to Sharp TV protection troubleshooting and protection on Sharp TDA93xx televisions.

More information about the original symptom is available in Sharp TV with TDA9381 and no picture.

Conclusion

For this Sharp TV TDA9381 case, the television had normal sound and OSD but no picture, and the measured ABL voltage was abnormal. Inspection revealed an open R604 resistor. Check the ABL circuit, R604, R605, and their supply paths before replacing the TDA9381 IC.

FAQ

Why does the Sharp TV have sound but no picture?

Possible causes include faults in the video processing circuit, ABL circuit, or associated components. The presence of OSD helps narrow down the diagnosis.