No FM - Marantz SR25 - LA1231

Member
Joined 2004
Paid Member
Hi all.
I barely know what I am doing in the world of tuners. I have the above receiver and it has absolutely no FM reception.
When testing, all transistors seem to behave correctly.
I found a chip with some very weird voltages. It's the LA1231 FM IF system chip.
Voltages are:
1) 0.072v
2) 0.06v
3) 0.06V
4) 0v (GND)
5) 0v
6) 0.07v
7) 0.239v
8) 0.237v
9) 0.239v
10 0.237v
11) 13.7 (Supply)
12) 0v
13) 0v
14) 0v (shorted to GND via PCB)
15) 0.017v
16) 0v

According to all info I can find, Including LA1231 datasheet and service manual, all voltages are very off (except pins 11, and 4).
Is this looking like a bad IF chip to anyone? What should I check more/next?
How would you go about restoring the FM receiving abilities of this unit?

BTW:
The receiver had no AM reception and while on FM, the "FM Stereo" indicator was on, permanent. But I found a defective resistor supplying the power supply to KB4431 MPX chip. Now AM seems to work (I think) and the indicator is now null, as it should be.
 
Hi
Check all the electrolytics around the chip. One is on pin 7, one on pin 5. Then the one on 12 via a 2k2 resistor and so on with all the ceramics. If they are good, look for a new chip. Which you will mount on a socket.