Onkyo TX-901 FM Section issue

rocknroller

Active Member
Have this receiver with an odd FM problem. It exhibits 2 issues:
1) It won't auto-tune any station in (with good antenna/coverage) but manually tunes in stations fine
2) The entire gain of the FM audio is *substantially* lower than every other input on the receiver, including AM. Subjectively - half the gain.

Block diagram below. The schematic is not great quality and I can't even fit the entire FM path on one page. 1st portion shown here as well but thought maybe I'd expand the relevant section (if identified from the block diagram) and repost it with better readability/detail.

This receiver doesn't have a lot of value but if there is something quick/simple to check or focus in on I'd love to hear any expert recommendations!

onkyo TX-901.jpg
onkyo TX-901 - Fm.jpg
 
Page 21/22 of the service manual. Do step one with a volt meter between TP1 and TP2. If this isn't adjusted to zero it will never auto tune.
 
Thanks - I'm seeing 3 volts there between TP1/TP2. No change L101 gets it back to 0 or even close, even at extreme settings. Best I can get is 2.7vdc. Zoomed in schematic in that area below, but still very difficult to read901 - fm -1.jpg
 
What are you adjusting with? Should be a non-conducting alignment tool. Also you can't be near any other station. Need to be at a dead spot.
 
Set with plastic driver, end of dial no stations tunes in. I don't see this as a (specific) tuning issue, though obviously affecting the auto tune. It strikes me more of a parts failure problem because the the voltage there that shouldn't be there. Also given the substantially lower gain of the whole output signal, it's like a part in the gain stage has failed
 
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