NEI 11ak03 free download

File name 11ak03.txt

11AK03 /VESTEL 5544/5417 CHASSIS SERVICE NOTES #G This Chassis is fairly conventional with no nasty suprises. It is software controlled via an I2C bus system,modular construction making servicing easy if extension cards are used, difficult if not. A switch mode power supply isolates the Mains input from the user electronics. #1 AUDIO STAGES This is a dual module solution where the Nicam module is mounted on the Audio path module. The Audio module is a Quasi parallel circuit with IC301 a mono Fm sound detector. The output from IC301 passes to IC307 a 3 input audio multiplexer, the output from IC307 goes to IC308 volume control and tone control. IC308 is controlled by the I2C bus, output from IC308 goes to IC309 Audio output stage. IC305/306 are Op amp buffers with filtering, which buffers Audio signals from the Nicam module and feeds them to audio multiplexer IC307. The audio select on IC307 is via TR301/302 and is controlled from the Nicam panel should a mono or stereo signal be detected. (see section 9 for Nicam section). NO AUDIO OUTPUT Check supply lines to all devices +28V to IC309 and +12V to others. Check with scope signal path. If audio into IC308 and not coming out, check the I2C bus. It is possible that an I2C bus contention not connected with IC308 has happened and the fault could be else where. NO AUDIO OUTPUT IC309 DESTROYED OR GETTING HOT. Check for oscillation on the output pins, if both channels are oscillating check C373, if one channel is oscillating check Zobel components on faulty channel ie C361 & R338/ C360 & R339. LOW LEVEL MONO SOUND (Nicam ok). Check alignment if YL302. ONE CHANNEL MISSING (Probably Nicam). Check signal paths with scope. #2 COLOUR DECODER (CHROMA PATH). Composite video is fed to IC401 pin 14, and chroma exits via pin 5, to IC402 pin 30, chroma is then processed and exits IC402 as B-Y and R-Y on pins 27 & 26, to IC403 a digital delay line via pins 9 & 12. The delayed chroma outputs from pins 10 & 11 back to IC402 via pins 21 & 22. The chroma is then fed to the Crt panel as RGB from pins 13, 15 & 17. Text and OSD data is fed into IC402 via pins 14, 16 & 18. NO CHROMA. (OSD & TEXT OK). #3 CRT BASE #4 HORIZONTAL OUTPUT #5 I.F JUNGLE #6 KEYPAD/IR MODULE #7 LUMA PATH #8 MICROCONTROLLER #9 NICAM MODULE This is a conventional Nicam module, mounted on the Audio module. This panel is mixed technology utilising Surface mounted and conventional components. Protocol and switching is via the I2C bus. Intercarrier sound is fed to pin 3 IC302 via Block filter L308 and TR303 & TR304, the signal is then passed through low pass filters via pins 6/7 and 5/8 IC302 and emerges as serial data from pin 15 IC302. The serial data is further processed in IC 303 going in via pin 21 and out in bus form to IC304. The audio comes out of IC304 from pins 6/8 to connector PL305 pins 1/3. NO AUDIO (Muted Sound) may outpu