ROADSTAR CTV1418XKT
Service Manual

6. Descr iption of microprocessor and TXT in CTN chassis Description
MICROPROCESSOR + TXT The CTN model chassis is designed to accept three different microcontrollers: the TMP47C634, the SAA5288 and the SAA5290. The three microcontrollers are mounted in the same position, by placing pin 1 at the same point. The TMP47C634 has 42 pins while the SAA52XX models have 52 pins. The circuitry connected to the pins is practically the same. From pin 21 on the Toshiba model, the equivalent pin on the SAA52XX unit will be 10 numbers higher (e.g., pin 33 on the TMP47C634 corresponds to pin 43 on the SAA52XX).

The difference between the TMP47C634 and the SAA52XX is an improvement in the OSD (it goes from two lines to a full screen, thus making it possible to implement the MENU) and the addition of new functions in the software (24-h timer, child block, etc.). The SAA5290 also has a TXT decoder. Following is an explanation of the different functions of the microcontrollers with indications as to the pin number assigned to each integrated circuit and the differences between the microprocessors, where applicable: - Integrated circuit power supply: The TMP47C634 has a single +5V power supply (pin 42 VVD). The SAA52XX has several power supplies for the microcontroller (pin 44 VDDM), the analog converter and the OSD (VDDA pin 38 and VDDT pin 39), as well as for the final phase of RGB outputs (RGBREF pin 31). - LED (pin 20): The LED lights up with a low current when the television set is ON and with a high current when the set is on Standby. - RC5 (pin 35 on the TMP47C634; pin 45 on the SAA52XX): The commands transmitted by the remote control handset are received by infrared receiver 1685 and passed to the microcontroller for decoding. - Switching voltages of the BG/L-L/L�-BG/I systems (pins 36, 37 and 38 on the TMP47C634; pins 46, 47 and 48 on the SAA52XX). These signals are only used on Multistandard units. These pins are used for switching the system for decoding sound and video. These signals are inverted and set at the correct level by transistors 7672 and 7673, respectively. Once they are transformed, together with the signal from pin 48 (BG/I), they make up the system status lines (See table). - Oscillator: The TMP47C634 has a 4-MHz oscillator which is determined by a 4-MHz ceramic resonator on pins 31 and 32. The SAA52XX has a 12MHz oscillator which is determined by a 12-MHz crystal between pins 41 and 42. - On-Screen Display (OSD): In order to synchronize the OSD information with the picture signal, the VERT FLYBACK signal is added in inverted form to the integrated circuit (pins 15 and 27 on the TMP47C634 and pin 37 on the SAA52XX), as is the HOR FLYBACK signal (pin 26 on the TMP47C634 and pin 36 on the SAA52XX). The SAA5290 also uses these signals to synchronize the TXT. On the TMP47C634 there is an LC network on pins 28 and 29 which controls the OSD. The TMP47C634 has only the green output activated (pin 23) and this is inverted with transistor 7658 so that the correct level is reached. The SAA52XX models have three outputs, R, G and B (pins 32, 33 and 34) with emitter followers (7641, 7642 and 7644). The pin for erasing the RGB picture signal for inserting OSD (pin 25 on the Toshiba and 35 on the SAA52XX) is connected with diode 6679 to pin 21 on the TDA836X. - Tuning: The unit has a VST (Voltage Synthesized tuning) system. This system works by tuning to a station on the tuner through a linear variation of the tuning voltage (0V2 to 5V). It is available on pin 1 of the mC and converted to an adequate level on the selector/dial (0V to 33V), using T7605 and +101.5V. The AFC signal (Automatic Frequency Control) of detector FI is added to the tuning voltage V-VARI by R3689 and R3688 to compensate for the slow variation of the tuning feature. While searching for the station, pin 41 is set on high which means that the AFC voltage will not be added to the V-VARI. If an IDENT signal is received on pin 16 while searching for a station, the mC will check via entry pin 9 whether the tuning is correct and whether the AFC signal can be activated again. The SAA52XX has 3 pins (15 VHF1, 17 VHFIII AND 18 UHF) for band switching and provides voltage to the corresponding pin. The TMP47C634 has only two pins (17, 18) for band switching which decode the 3 tuning lines using transistors 7003 and 7004. The SAA52XX models also have pin 30, which they use to limit the CAS voltage in automatic tuning so that noise signals are not memorized. - Picture and sound adjustments: volume control (pin 2), brightness control (pin 3), colour control (pin 4) and contrast control (pin 5); the SAA52XX models also have sharpness control (pin 6).

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