The fault is intermittent. At times, when the main switch is pressed, the front red standby led remains OFF and other times it regularly lights up and the unit switches ON. The customer decides to always leave the unit in stand-by mode and the problem is resolved in this way. But if there is a sudden power cut then the problem re-occurs and the red standby led is OFF. Maybe the fault has got worse, I hope so as if so it will be easier finding the cause.
The chassis on this model 100 Hz is part of that series of modern ones produced by Mivar in Italy, in which the power supply is not separate from the chassis structure but is part of it. First thing I replace C8 (100uF-35V) and C9 (470uF-35V), but nothing changes and the power supply is not operating. On pin 16 of the chip regulator IC1 (TEA 2261) the tension is very low instead of the 12V it should have.
Besides I see a full tension of 300V is present on the electrolytic capacitor terminals C12 (150uF-385V); when the current is removed from the unit this tension does not decrease at all. After various testing I find that when 12V are present on pin 16 the standby led illuminates. I decide to replace the Controller chip TEA 2261. The replacement of this component is rapid.
I press the switch on and the standby led switches on regularly. When a programmed key is pressed on the remote control the TV switches ON, the audio and video are both regular. After various testing and check outs the repair gave me positive results.
Out of curiosity I decide to measure the voltage on the terminals of the smoothing CAP, I see that on removing current, this voltage quickly decreases, the opposite to before. The replacement produced a fully working unit, so now it can be re-delivered to my customer.