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Hitachi SR 303L

I put the multimeter in VDC, the voltage difference between TP2 and TP3 is between -20mV and 30mV when i tune the strong 104.3 radio station. I have some problems locating pin 17, the datasheet said to have 18 pins but in the receiver it has 20 pins? I locate R209 and C214, pin 17 point to here, i measure the voltage in this point, and get 1.7V with FM mute off and 1.5V with FM mute on.

I post a picture on: http://ge.tt/8K3ClZV2/v/0?c
 
The voltage you measured is enough to drive the HA11211 chip into the muted condition.

I think the most interesting question is why a positive voltage exists at that point, even when the muting switch is set to off. Can you measure at both terminals of R209 and see if there is a difference? If there is a difference, does the terminal that is connected to the chip pin 17 have higher or lower voltage than the other terminal?

You could also try connecting pin 17 to ground, to see if any sound is heard in that condition.

About the appearance of 20 pins: I think that the chip is asymmetrical, with 10 active pins on one side and 8 on the other side. Very unusual!

(Edit: I had asked for a confirmation that the chip is marked HA11211, but I looked at the picture and I see that it is.)
 
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Yes , the chip 11211 is asymmetrical. About R209, the difference between terminals are 0.5V, the terminal connected to pin 17 is lower voltage; the other terminal is connected to FM mute switch.

I connect this terminal of R209 to ground and the FM starts to work! What's happens? The FM mute switch is bad?

Edit: now, i test the FM mute switch and it's working normally.
 
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You are in good hands with chazix. Check and clean the FM Muting trimmer. It could be bad, dirty, or have a cold solder joint.
 
It is an unusual failure, but I would have to conclude that the FM muting switch formerly had sticking contacts, such that the mute signal was being passed to the HA11211 even though the switch was set to off. Operating the switch must have freed the sticking contacts. It would make sense to clean that switch with contact cleaner.

This still leaves a question: Why was the muting signal (which comes from pin 10 of the HA11211) active, even though the receiver was tuned to a strong station? If that signal is active, it will disable stereo decoding, even if the muting switch is set to off.

Regarding "FM Muting trimmer" - in this receiver, I don't know what that could refer to. There are no muting adjustments.
 
I'm very happy, thank you so much chazix. I already had cleaned all the switchs with "Abro Contact Cleaner" but i try again. I will disassemble the front panel to better access to fm mute switch, i test the upper side of button with the multimeter and it switch off-on normally but there may be a fail in the solder joint below the board.

The switch is like this: http://i01.i.aliimg.com/img/pb/214/647/825/825647214_699.jpg

The stereo indicator looks like a led but it was a lamp (5V 30mA) with a red plastic cover and is burned, i have to get a replacement for it.
 
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It's nice to see the receiver re-assembled - I hope that means that it is working satisfactorily for you.

Congratulations,

chazix
 
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