No FM in a Philips B4X82A (Techniek Radio/TV)
Hello All,
I saw this forum and wondered if you could help me.
Someone gave me this radio.
I made the first repair steps : replace the filtering capacitors and all paper capacitors.
The radio is now working in AM but nothing in FM !
This is not a keyboard problem. The ECC85 is good.
I get no signal on S107. I should get something there with my oscilloscope I guess.
Could you help me ?? What should I first look ?
Thanks a lot !
Stéphane
No FM in a Philips B4X82A
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
No FM in a Philips B4X82A
door henkk , Alkmaar, 09.08.2011, 07:53 (4856 dagen geleden) @ tyrell
Did you replace the electrolytic capacitor of the ratiodetector,when it is shortened there is no sound at all on FM.
Remember that the + pole must be connected to the chassis.
Henk
No FM in a Philips B4X82A
Yes, I replaced it. Value is 3.2µf.
But you are right in that there's no sound at all, not even the typical FM "white noise".
I think the problem lies in the FM head.
Thanks
Stéphane
No FM in a Philips B4X82A
door Ouwe Schipper , Sassenheim, 09.08.2011, 10:24 (4856 dagen geleden) @ tyrell
"I think the problem lies in the FM head."
Well Stéphane....
Anyway I'd start injecting 10,7 Mhz the way I mentioned, just to make sure.
After finding this FM IF amplifying and detecting allright I'd continue with the oscillator check I already mentioned. Some way or another in my memory has popped up a similar problem, which some time ago has been solved by replacing C116
Don't blame me if I remember wrong
Nico
No FM in a Philips B4X82A
BTW I get 0v on pin 2 and -0,3 on pin 7.
200v on pin 1 and 134v on pin 6.
Stéphane
No FM in a Philips B4X82A
door Ouwe Schipper , Sassenheim, 09.08.2011, 16:42 (4856 dagen geleden) @ tyrell
Well if there's just -0,3 on pin 7; and while doing that measurement you had this extra tip resistor as I advised....
It it pretty sure that the self- oscillating mixer ECC85 second half does not oscillate. In that case there is nothing to mix and nothing in the range of 10,7 Mhz will appear on coil S106.
The voltage across R 102 should be at least about -3 volt
Next thing is to find out why this oscillating does not work
But yet, I advise you to check the IF amplifying and detection concerning the FM section. It's such a simple check, the way I described....
Nico