The defect arose as an irregular occurrence of a short circuit message in the drop cableĪfter turning the device off / on, the message appeared again after a short time. After replacing R2, the device is restored to working condition. Since the resistance between the 3.3 V power pins of the decoder chip and the circuit ground was unity Ohms, it was replaced. The supply voltage at the STi5119ALC decoder (3.3 V) is absent, the resistor R2 (1. The tuner does not turn on, the voltages generated by the tuner power supply are normal The Q1 power key transistor has been replaced with a more powerful type MJE13007. Replacement of these elements led to the restoration of the tuner. Mains fuse A1 (2 A) blown, key transistor Q1 (MJE13003), the PWM controller U1 (THX201) and the Zener diode DZ1 (6.2 V) also failed. In addition, an electrolytic capacitor with a capacity of 100 μF x 10 V was connected in parallel with C1 (0.1 μF), which improved the sound quality of the broadcast programs. It was eliminated by replacing the EC4 capacitor (10 μF x 16 V) in the WM8725 DAC circuit. The defect is manifested in the periodic appearance of RF noise components in the soundtrack The performance of the tuner was restored after replacing the Flash-memory and writing the standard firmware to it. Soldering of the Sti5518 decoder and Flash-memory, as well as control of the connections between them did not lead to positive results. It turned on normally at the first start, but after entering standby mode it became uncontrollable. Writing a working firmware in U381 temporarily restored the tuner. Checking the U381 Flash-memory (HY29LV160ATTC-90) showed a mismatch in its contents compared to the reference firmware. The voltages generated by the tuner power supply are normal. When you turn on the tuner in the network, it does not switch to standby mode The defect is eliminated by replacing the voltage regulator U151 (LM317) in the voltage generation circuit +14/18 V. There is sound, there is no image and on-screen menuĬhecking the +14/18 V voltage injected into the drop cable to power the external converter showed that it is normal when the drop cable is disconnected and is very underestimated when it is connected.
After replacing the U721, the fault was resolved. The supply voltage of the U721 chip (+5 and +12 V) is normal. 32) the video signal is present, and at the output of the U721 video switch (AK4702VQ) (vyv. After soldering the resistors, the defect was eliminated.Īt the output of the U301 decoder (STi5518) (vyv.
Oscilloscope monitoring of the TS MPEG-2 transport stream signals from the BS2F7VZ0184 channel selector showed that they do not pass through the resistors RA101, RA102 to the STi5518 decoder chip. On-screen display (OSD) is displayed, the voltage of the external converter is normal. Due to the fact that many of these defects can occur due to damage to the control program of the microcontroller, you should first try to restore it, as described in. It should be noted that the material contains hardware malfunctions of the tuners. Therefore, it will be very useful to have an idea of \u200b\u200bthe symptoms of defects and methods for their elimination. Since many tuners are designed according to similar schemes, the defects of some models are similarly manifested in other devices. The article provides typical and once encountered in the author’s practice malfunctions of satellite television (STV) tuners and methods for their elimination. Main page » Scheme Satellite tuner signal level does not rise.
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