Restoring/Rebuilding/Repairing a NAD 7240PE Reciever
Before I begin, I would like to give you guys a little background information on this unit, and why I am doing all of this. The NAD 7240PE was a mid-range receiver, conservatively rated at 40 watts/channel. Two versions were made; one with a simple, red, seven-segment display (this one), and one with a newer, green display. The board layout and wiring is slightly different for both versions. The overall design and schematic is exactly the same for both versions.
This unit in particular was given to me by my father. It was my first piece of "good" audio equipment and holds a special place in my heart. However, the right channel seems to be dying, and the display is going out. My plan is to restore this thing back to its original glory, and maybe improve the design where possible.
One thing to remember about NAD units was they were built to a price-point. NAD's philosophy was audiophile on a budget. You can see this in their units...
Don't expect clean wiring, easy board access, or quality components. The design of these units are another story...
While the 7240PE is rated at 40 watts/channel of steady-state power, its +6 dB of IHF dynamic headroom means that its dynamic power for musical transients exceeds 160 watts/channel at 8 ohms and 200 watts/channel at 4 or 2 ohms. Even with long 200-millisecond tone-bursts, representing the full
duration of musical notes and chords, the 7240PE produces an impressive 100 watts per channel.
When the amplifier is driven beyond its rated power, NAD?s famous Soft Clipping circuit gently limits the waveform and prevents the harshness that occurs in other receivers when the output transistors arc driven into saturation. Unfortunately, this area of the circuit/design is error-prone and overheats frequently. IMHO it is best turned off.
Now that you have a bit of background on the unit, here are some of this projects goals.
--- Preform a complete cleaning of all controls, boards, and parts of the unit (Deoxit, flux-removal, and general cleaning)
--- Repair the right channel output
--- Replace all electrolytic capacitors
--- Fix the faulty display
--- Fix the soft-clipping circuit
--- Adjust and align the tuner section
--- Add a new, quality power cord
Now for some pictures of the unit...
In my experience, before you try and repair ANY piece of audio equipment, please obtain a service manual! You might be able to find a scan from online, but it is best to have a good, quality hard-copy as well. I find it nice to take notes in for updating information or correcting errors. I also like it when I am ordering new parts. I often right down links to parts or any notes about their specs and availabilty.
Rick and StereoManuals.com has literally thousands of reproduction and original service manuals. While the price maybe high, the service and quality speaks for itself.
Link to NAD 7240PE service manual.
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