HELP! NAD 7240PE tuner

[HendeoNZ]

Hi all,

I have a NAD 7240PE with a tuner problem and was hoping for some help troubleshooting.

The amp all works expect for the FM band. I get no sound and not auto seek or station lock.
The AM side seems to work (I can pick up stations). But the seek is a bit touchy.

I thought it might be a bad cap, so I've replaced most of the bigger ones on the tuner side - no luck.

Is anyone able to help me solve this problem?

Cheers

 

[ryuuoh]

maybe this thread will point you to some troubleshooting:
https://www.diyaudio.com/forums/solid-state/160737-nad-7240pe-dead-tuner.html

 

[HendeoNZ]

maybe this thread will point you to some troubleshooting:
https://www.diyaudio.com/forums/solid-state/160737-nad-7240pe-dead-tuner.html

Thanks, I've already looked at that post. I'm starting to suspect the IC's but I don't really know.

 

[HendeoNZ]

Update

I found the IC3 (FM IF DET) has 15v coming in on pin 11 and nothing coming out except for pins 8 and 9 which have 1.1v each. The chip is a LA1235.

Cheers

 

[petehall347]

verify grounding first and negative supply .
thats just of top of my head .

 

[Ylli]

I found the IC3 (FM IF DET) has 15v coming in on pin 11 and nothing coming out except for pins 8 and 9 which have 1.1v each. The chip is a LA1235.

Doesn't sound like a very healthy chip. B&D lists it as in stock, https://www.bdent.com/la1235-sanyo-audio-16-pin-dip-integrated-circuit.html

 

[HendeoNZ]

Ch

Doesn't sound like a very healthy chip. B&D lists it as in stock, https://www.bdent.com/la1235-sanyo-audio-16-pin-dip-integrated-circuit.html

Cheers for that. I've got one on it's way.

 

[HendeoNZ]

So one thing I probably need to sort out is the high voltage going to Vcc of the LA1235 IC. Currently it's around 15.2v and the chips max is 16v.
I should probably fix it before I put in a the new chip. So I've done some probing around the board and most voltages are close to what they should be.
But it looks like R17 120ohm 1/4w isn't doing anything - but it still reads as 120ohm.

Anyone got and ideas?

Cheers

 

[petehall347]

it will read like that if no load present

 

[Ylli]

Yeah, power comes from a +15 volt source, through the AM/FM switch (SW14), then through that 120 ohm resistor to IC3 pin 11. As petehall347 say, if the chip is not drawing current, there will be no drop across the resistor. Even if it doesn't come down (and it should), you are OK at 15.2 volts.

 

[HendeoNZ]

Yeah, power comes from a +15 volt source, through the AM/FM switch (SW14), then through that 120 ohm resistor to IC3 pin 11. As petehall347 say, if the chip is not drawing current, there will be no drop across the resistor. Even if it doesn't come down (and it should), you are OK at 15.2 volts.

Cheers for the response.

 

[jhjove]

Thanks, I've already looked at that post. I'm starting to suspect the IC's but I don't really know.

That diyaudio post mentions cracked solder joints, have you checked or gone over solder joints on the boards?
These typically occur in high heat areas but in my experience with NAD, boards could get a bad solder joint anywhere.

 

[HendeoNZ]

That diyaudio post mentions cracked solder joints, have you checked or gone over solder joints on the boards?
These typically occur in high heat areas but in my experience with NAD, boards could get a bad solder joint anywhere.

Thanks for the reply - Yeah, I've been over the whole board and touched up anything that look suspicious - Cheers

 

[HendeoNZ]

Thanks for everyone's help. I replaced IC3 and the Crystal oscillator - now everything works.

Hopefully this can help anyone else who has a similar problem.

Cheers

 

[Ylli]

The Crystal oscillator? ???

 

[HendeoNZ]

There was a problem with the auto seek - after some research it was suggested that the oscillator could be the cause (not related to the IC3) so I swapped it out - seemed to do the trick.

The Crystal oscillator? ???