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Old 6th February 2010, 03:16 AM   #1
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Default NAD 7240PE Dead Tuner

I'm in the need of some expert advice!

I acquired a 7240PE for next to nothing. Amp section works great with CD source but tuner is dead. Front panel lights up but no sound at all from the tuner. The FM stereo light never comes on even when tuned to known stations.

I'm no electronics expert but can handle some basic troubleshooting. I checked the output from the tuner power supply transformer. From the yellow wires, I get 5.6 and 5.9V AC. From the blue wires, I get 22.4 Volts on one and 0V on the other (according to my schematic, I think I should see 12.2V on both blue wires). My schematic is for the 7220 but it would seem that they have the same tuners.

Is my problem as simple as a bad tuner supply transformer? Any fixes (other than the obvious replacement), or any other recommended tests to perform?

I'd greatly appreciate any troubleshooting assistance any experts could give. I can forward a copy of my schematic if any gurus are willing to help.

Thanks!
Matt
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Old 6th February 2010, 03:34 AM   #2
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Disconnect the output wires from the transformer and check it no load for AC voltages.
This will show if the transformer is being overloaded or not.
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Old 6th February 2010, 08:36 PM   #3
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Okay, disconnected the load from the transformer. Ac voltage across blue wires is 24V , AC voltage across yellow wires is 12.7V. These numbers seem to make more sense.

I realize now that I was measuring my voltages to ground before, rather than across the two wires. (I have more experience in the DC world).

I have a good quality multimeter and some basic electronics knowledge, I'd really appreciate any help in determining the next steps in troubleshooting my tuner!

Matt
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Old 8th February 2010, 05:40 PM   #4
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I'd still love some help troubleshooting my tuner.

As mentioned before, the pre/amp sections of the 7240 work great. The tuner display lights up but is dead silent and won't lock on to any station.

I think I ruled out the A/C power supply to the Tuner, so i guess I need to start troubleshooting the tuner itself.

I have a tuner schematic for a similar NAD reciever (7130 I think). It looks like the tuner is identical so I've got that to work from. I've noticed about a dozen TP (test points?) on the tuner board. Is there any tests I should be performing?
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Old 30th December 2010, 06:03 PM   #5
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I recently tried reviving a 7240pe. Replaced almost all of the capacitors in the tuner and preamp sections, and even swapped out some op-amps with good results. The tuner was great for a while then it started having issues recently. It just won't lock in on a channel. I get sound. Seems to need adjustment and perhaps some of the parts I haven't replaced have failed.

The amp section is toast. Might be worth fixing but the heat sink is too small.
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Old 2nd January 2011, 12:30 AM   #6
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I was reading through the service manual. There are quite a few adjustments that can be made. I'm guessing things are out of spec. I don't have much for test equipment but a DVM will at least give a clue. Get the service manual and start measuring.
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Old 2nd January 2011, 02:04 AM   #7
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What usually is the problem in amplifier sections (especially in equipment that has had a "questionnable" past) is the power transistors have been damaged. Along with them they can take out the the driver transistors, so you'll have to remove all the transistors (that's at least four per channel: two output transistors in either TO-220 or TO-3 packages and one driver per output transistor) and verify them with a multimeter.

then again it could as simple as the signal links in the RCA Pre-out to Power amp-IN missing...

Whatever the problem is, make sure you have No D.C. on the speaker outputs, Highest level acceptable would be around 100mV, and even that's a bit high.
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Old 28th July 2012, 06:45 AM   #8
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Greetings DIY'ers.

For others who may need information on this issue, I am reviving this old thread.

Over the last two days, I have successfully resurrected my NAD 7240PE's tuner section which exhibited the same issues that the original poster discussed above. It slowly became intermittent and finally just quit, no audio (not even hiss) and no signal meter lock.

I have seen this happen before with other receivers and generally, I have found it to be a power supply issue. I attacked this the same way: I found low voltages on all the VS rails of the tuner board (there are several supply voltages). I replaced ALL the electrolytics in the tuner's PS section with Panasonic FM or FC series. Then I went through the smaller voltage regulation caps in the localized networks, especially in the area of the FM synthesizer and crystal oscillator. There are some small value e'lytics in these areas (0.1uf; 0.22uf; 0.33uf). I have heard of people using the Panasonic ECQ series of stacked film caps instead of e'lytics for these smaller values, though I had great results with Nichicon FW series e'lytics.

I replaced every electrolytic in the audio path with the premium grade Nichicons, a few Blackgates and Elna Silimic's for C91 and 92. The 7240's tuner now finds stations in a snap and the audio quality is excellent. The FM Noise reduction network now works much better as well. I have not yet done a tuner alignment, but I expect performance to get even better once that is done.

One thing I noticed in doing this job is how poor the wave soldering is on the board. Especially around the IC's... many cold solder joints. I went carefully through these with solder wick and re-soldered them, being careful not to over-heat anything.

Another problem area on these NAD tuners may be the two voltage regulating 5V and 15V IC's (IC 801 and 802 respectively). I think that when the PSU caps begin to dry up, it places undue stress on the regulators and they can begin to act up. If you get into this job and are ordering parts, add the regulators to your list "just in case" (78M05A and 78M15A) as they are very inexpensive. Also, I think there may be modern equivalent regulators today that are quieter. Someone here may know more about this.

At any rate, I invested about 8 hours of labor, maybe 4 hours of research, and about $35 of parts into this. If you happen to like these units (very lively and dynamic), I can definitely say this is worth doing as the upward improvement is palpable.

Hope this helps,

Allen

Last edited by Corona Blue; 28th July 2012 at 06:56 AM.
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