No Sound from NAD 7240PE

Are you getting the correct voltage at Q501 emitter or R311, 312?
Expect +/-14V at these R's.

If the voltage is ok then best to follow the cleaning procedure outlined previously in this thread.

If the voltage is not ok then suggest you measure voltage at Q501 base at junction with R505.
Expect about 20V, if this is not OK then pull out R505 and R511 and replace C515.
 
I did fiddle with the receiver a little more and found that it takes about 15-20 seconds to get some sound when turned on
I'm surprised you are getting any sound at all, especially if the positive rail is only showing a few volts.

and sometimes it keeps playing for about 10 seconds after it is turned off.
This is strange.

Put the 2 observations together, something is taking a long time to charge up (power ON delay) and then a long time to discharge (at power OFF).
The easy answer would be to say the power supply caps are tired and should be recapped. However, since the opamp is barely working it
does not have the normal current draw, maybe causing the power off delay...
 
these nads are rubbish btw
At the risk of offending the NAD fraternity, the best thing I can say about NAD's of this vintage is they were cheap
and delivered a good sound for the money BUT that sound is not inspiring or even good compared to the vast
array of amps/Rxr's that can be had quite cheaply. I've spent huge hours on a 3150 (recap twice, opamp, rectifier
and, and,,) only sounded ok. Refurb'd 3x3020's, ok but not keepers and a 3140 which I think deserves more time.

For me, the entry point should be the Yamaha CA-800, or sansui AU-505, or Luxman SQ-507X, or,,,
There is so much good vintage gear out there and reasonably priced...
 
the mute circuit is probably not working as it should

What I thought "inductor" was talking about was the protection circuitry/relay that suppresses that annoying power OFF/ON
thump. Basically, the speakers aren't connected until after the power ON thump has occurred, maybe 5seconds or so. Likewise,
at power OFF the speaker connection is broken asap to prevent the power OFF thump going to the speakers. Now, if the
protection circuitry is not working properly, that 5 seconds may be 10 or 15 or... will have a look at the schematic.

Need you to followup on actions in post 41.
 
To Drum and mbz: a delay on start up or shut down is not normal on these units (or, at least mine). Additionally, I don't recall seeing a speaker protection relay in my unit, and I could not identify one from a quick look at the schematic. I could be wrong, but I think the only protection on these units is provided by the internal fuses.

I agree with mbz that the first thing to do is make sure the voltages are within spec and fix what needs to be be fixed for that. It is possible the other issues will go away once that is done.
 
Are you getting the correct voltage at Q501 emitter or R311, 312?
Expect +/-14V at these R's.

If the voltage is ok then best to follow the cleaning procedure outlined previously in this thread.

If the voltage is not ok then suggest you measure voltage at Q501 base at junction with R505.
Expect about 20V, if this is not OK then pull out R505 and R511 and replace C515.

I was out of town yesterday. Back now and took some measurements.

Voltage at Q501 Emitter is 1
Voltage at R311 is 1 (2)
Voltage at R312 is 18 (20)
Voltage from Q501 base to R505 is 14 at one end and 0 at the other.
 
Good luck with this. I read most of it but was intially worried the preamp poweramp jumpers were disconnected or fritzed.
 
NAD Resistors.JPG More information.

I went back to double check some of my earlier tests and it looks like I may have been confusing R510 and R507. I thought R507 was on the right with the label below but maybe it is on the left with the label to the right.

I will just call them left and right for now.
Q501 Collector to the left resistor is 28 volts
Q501 collector to the right resistor is 0 volts
Impedence for the left is Infinity
Impedence for the right is 68

OK - may be on to something. Was double checking the voltage from the left resistor (bottom) to Q501 collector and accidently had the tester still on ohms. suddenly everything worked perfectly (as long as I left the test leads in place). Huge amounts of volume, loudness worked, bass EQ worked, the tone controls even worked (just discovered that they also had not been working).

So it would seem that the solution is at hand. I just need a little help deciphering all of this. Thanks for all the help so far -
 
Voltage at Q501 Emitter is 1
Voltage at R311 is 1 (2)
The positive power supply to the opamp(IC301, pin 8) is still down. At best the sound will be garbage, expect no sound.

Voltage at R312 is 18 (20)
The negative supply to the opamp is a little high but this is expected to fall when the +ve supply is fixed and the
opamp works/draws the normal current.

Voltage from Q501 base to R505 is 14 at one end and 0 at the other.
This measurement is only partly helpful. Prefer measurement with black probe connected to chassis.
This suggests the voltage at the zener is at about +16V. The low base voltage suggest and high current through R505
point to C515 (47uf/25V). Replace this cap first. If voltages are still not ok then proceed with the suggestions below.

The voltage at Q501 base is expected to be about 20V
Need to unsolder one side of R505 and lift that leg out of the circuit board and then measure its resistance, expect 1k
Do likewise with R511
 
Yes, R507 is on the right as described. Blue/grey/black bands
indicate 68ohms.

On the left is R510, Blue/grey/yellow bands indicate 680Kohms
Q501 Collector to the left resistor is 28 volts
OK, due to Q501 not working normal

Q501 collector to the right resistor is 0 volts
ok

Impedence for the left is Infinity
Expect 680kohms

Impedence for the right is 68
As per spec, good.

Was double checking the voltage from the left resistor (bottom) to Q501 collector and accidently had the tester still on ohms. suddenly everything worked perfectl

This mistake normally results in sparks and a trip to the bathroom to clean up. VERY DANGEROUS.

The multimeter has established a connection between the 2 point/bypassing Q501.
The good news is that this confirms a +ve supply psu issue. The bad news is the OPAMP has received +28V (or about)
which is enough for toast. Please don't do again.

Replace C515 (47uf/25V)
If voltages are still not ok at R311 (black probe on chassis) then lift leg of R505 and measure resistance. Repeat for R511.
 
Yes, R507 is on the right as described. Blue/grey/black bands
indicate 68ohms.

On the left is R510, Blue/grey/yellow bands indicate 680Kohms

OK, due to Q501 not working normal


ok


Expect 680kohms


As per spec, good.



This mistake normally results in sparks and a trip to the bathroom to clean up. VERY DANGEROUS.

The multimeter has established a connection between the 2 point/bypassing Q501.
The good news is that this confirms a +ve supply psu issue. The bad news is the OPAMP has received +28V (or about)
which is enough for toast. Please don't do again.

Replace C515 (47uf/25V)
If voltages are still not ok at R311 (black probe on chassis) then lift leg of R505 and measure resistance. Repeat for R511.

Replaced C515. Everything seems to be working now. Thanks so much.

Crazy how one tiny capacitor can make such a difference.
 
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Been using the receiver for a week now and still going strong.

I adjusted the MPX VCO because it was not holding onto stereo signals and that worked really well.

It does still have one minor issue. The tuner is off by .05. Instead of showing 100.10 it shows 100.15. the center tune shows it is good at 100.15. Can this be adjusted or is it set? It looks like the "Synth (L.O.) Freq." adjustment may help. I tried turning it a little but didn't want to mess anything up and put it back. Am I on the right track? Is there another place to adjust this or is it just gonna be stuck like this.

Not a big problem really - just curious.

Thanks.
 
Drum, glad you have it fixed. Love the nad sound. have a 3140 amp.

Love the sound as well. I also love the look (simple, straightforward and clear) and the features (has everything I need without the fuss of what I don't need)
 
Hey, this thread isn't too old so I'm going to try to resurrect to help me with a similar problem. Have a 7240 with a good amp and no sound from preamp. Voltage good at R311 (19 and 15) but not good at R312 (-19 and 60mv). I checked R312 and it seems good. Should I pull the associated Trans and check?
 
Vaguely recall that NADs use FETs for power on muting, Q201, Q302, maybe the control for these is down.
You would be unlucky if the opamp died, more likely something else. Assume no oscilloscope or audio probe?
 
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