NAD 705 No FM

Eastham

More Class-A than ever!
So I recently bought two NAD's, one of them has a problem with no FM the other has a completely dead tuner. This one seems to have an issue with no FM, the FM muting works until you try tuning when it just seems to stop working and all the tuner picks up is static, AM seems to work.

I've measured some voltages found some missing or wrong values. IC403 is missing voltages on pins 17 and 18. IC 401 is missing voltage on pin 4. IC 404 has 7v on pin 17 4.5v, on pins 18 and 19, pin 20 has 5v and pin 21 has 1.7v, I also noticed that Between TP 7 and TP4 is 31.5v which I believe is supposed to be 3v - 3.1v.

I've also checked my antenna is working and gets a very strong signal on my SX-737. Any help would be definitely be appreciated!
 
The voltage between TP 7 and 4, should change as you tune. It would be low around 3v at 87Mhz, if you tuned to 108 then you would have a higher voltage 25v or so.

A quick look over the schematics, looks like there are switching transistors that switch the operation from AM to FM. Would be where I would checking. Poking around with a voltmeter really isn't the best way to troubleshoot a tuner. Having a signal generator and tracing the signal with a oscope yields quicker results.
 
The voltage between TP 7 and 4, should change as you tune. It would be low around 3v at 87Mhz, if you tuned to 108 then you would have a higher voltage 25v or so.

A quick look over the schematics, looks like there are switching transistors that switch the operation from AM to FM. Would be where I would checking. Poking around with a voltmeter really isn't the best way to troubleshoot a tuner. Having a signal generator and tracing the signal with a oscope yields quicker results.

The voltage seems to stay at 31.5v or for some reason will drop to 0v no matter which part of the band and despite following the service manual's instructions L402 has no effect on it. I'll start checking the voltages at those transistors, I think I see which ones you're refering to though I don't know much about tuners. I do have a 'scope though it's only 20MHz, but it was good enough to show me that the FM oscillator is running at TP5.
 
Sorry for the late replay, I'm getting 32v on the collectors of Q409 and Q410 and I'm getting 17v on the emitter of Q401.
 
Another interesting thing I just noticed, the static gets louder when an antenna is attached, in my case a 75ohm TV antenna in my attic.
 
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