No FM in a Philips B4X82A (Techniek Radio/TV)

door Ouwe Schipper , Sassenheim, 09.08.2011, 06:32 (4856 dagen geleden) @ tyrell
Bewerkt door Ouwe Schipper, 09.08.2011, 06:53

To me, using an oscilloscope on S107 does not seem appropriate. The signal there (if any present) is very weak and the probe may disturb the tuning.
First thing to check is the oscillating of ECC 85 right half. The most simple way to check this is measure if there is a negative voltage on the grid (pin 7) Use a digital instrument (because of the highest possible input resistance). Do not forget to put a resistor of about 1M on the tip of your measuring probe! The purpose of which is not stopping the oscillator by parastic capacitance.
Another try is worthwile: insert a 10,7 Mhz signal from a generator on the metal screen of the ECC85 (after isolating this screen from earth) and measure if any voltage appears on C 40. The generator may have to be fine tuned around this 10,7 Mhz. If nothing happens, inject the signal on control grid of B2. If a voltage appears on C40 you have to check the path of the AF signal which should be across C38 (DC, varying with the tuning of the generator)
Let me know your proceedings
Nico