SONY WEGA - CONTINUOUS TUNING. NO TUNNIG LOCK. [SONY WEGA KV-TG-21L70 _ KV-TG21M80 _ KV-TG21P52]
In auto serch mode, set tunes to channels, but not lock them in memory. Tunig process goes on and on. No end.
This fault is mainly with the main system control section and tuner. check whether you can see glimps of stations, as set tunes on. If you can see it, make sure that the tuner to your TV is working fine, and the tuned stations are not stored in memory.
This is a bus type chasis. That is, all the other ICs are controlled by main system control IC [IC 001 _ CXP85***], by a data stream of two lines, serial clock and serial data from pins 55 & 53 respectively. whan a station is tuned in, the data will be transfered to it main system memory IC [IC 003 - M24C08-BN6(A)].
Check the voltage to this memory IC There are four pins (1,2,3&4) are connected together to ground. Pin number 8 of this IC gets 5VDC; and pin 5 gets data from main system IC, and pin 6 gets serial clock pulse. Check the voltages of these pins. Voltages at pins 5&6 should be around 4.3VDC. If pin number 8 have 5VDC and other two pins stated above gets 4.3VDC, and still the channels can't be memorized, the memory IC should be suspected.
Before mak it sure, chck thefrequency of these data and clock input pins [square wave], with the help of an oscilloscope, if available. If you haven't this testing equipment, try repalce the IC. This IC is very cheap to buy and available from most of the electronic spare part selling shops at your town. Make sure to use the exact number as specified, otherwise, the set will even refuse to swtcih ON. In most cases, to my service experience, I've found this IC to be faulty.
