Sony STR-D3-1

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Hi John,
Okay, the tuner pack is probably getting B+, but either the Vt line isn't working, or the LO out isn't functioning.

Are you an experienced audio tech accustomed to tuners? DO you have any test equipment you would need for this work?

-Chris
 
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I assumed you had an antenna connected.

Okay, so you know what to do. Check your IF out in the tuner pack. I think you'll only have power, control signals and audio plus ground out. You'll be working in the tuner pack. Also check the charge pump is outputting a tuning voltage to the varactors.
 
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Hi John,
Classic tuner packs used commonly 9, 12 or 23 VDC for top of band. That is varactor dependant. I have seen 3V3 supplies lately, so probably a step-up. If it isn't detecting a VCO output it will lock high or low.

My trick is to disconnect the VT line and feed a variable power supply in Start low and see if it can manually tune in low stations. now of course they may have added to the mix today. It is possible that unless the up locks to the VCO it may mute. All you can do is monitor the IF signal to see if it tunes in that case.

Common things that killed these circuits were coupling capacitors, typically short allowing DC through that would either drag the circuit down, or bias the input too high. Caps could also short in the charge pump. Now this is today, so maybe a different issue has cropped up. Occasionally a prescaler chip could fail. These are all likely on the chip today, no separate chips - hence no access to some signals.