Restoring/Rebuilding/Repairing a NAD 7240PE Reciever

VintageNAD

Not Always Defective
Restoring/Rebuilding/Repairing a NAD 7240PE Receiver

Hey folks,

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...

Note:

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.

http://www.stereomanuals.com/man/rep/nad/index.htm

I have a scan of the service manual for second version of the unit... (for units beginning at serial #A7401100001) If you need a copy, PM me.

Chris
 

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Fixing the display

First on tap is to fix the display board of the unit. Several bars of the seven-segment display are out; most likely due to cracked or corroded solder joints from flux/grime build up.

This unit is very difficult to take apart. The black wire jumpers are soldered to the boards and glued (JW104, JW102, JW303, and JW103). Luckily, we can just gently scrape off old glue with a pick. Now we can desolder the black jumpers to access the display board. We can cut off the old jumper strip about a half inch to strip new connectors.

NAD coated these boards with flux. Looks like we need to clean off the flux. Best to use a cheap, new toothbrush and some 99% isopropyl alcohol.

Once we are done cleaning the flux, we reheat all joints and resolder any problem joints. We will replace the small electrolytic capacitor (C601) with a Panasonic FM equivalent.

That is all for now.

Chris
 

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Just saying, as they seem to have a rep of failure. Might want to look into getting suitable replacements before they are unobtatium.
 
Being the "audiophile on a budget" that I am I also have always had a soft spot for NAD.

I have owned the 3020, a few receivers like the 705 and others plus have happily used the AV713 for many years though it has been relegated to the cabin AV system. It works admirably well there. I have the 5240 CD player at the cabin as well and just the other day picked up a 701, 6220 tape deck and the 5355e CD player. Those 3 were the cheapest yet and 2 of them I have already made to work perfectly. I just have to find that laser for the 5355e...

In addition to that I have repaired some other NAD stuff for friends. So anyway, what I am trying to say is I will follow this with interest. :)
 
Being the "audiophile on a budget" that I am I also have always had a soft spot for NAD.

I have owned the 3020, a few receivers like the 705 and others plus have happily used the AV713 for many years though it has been relegated to the cabin AV system. It works admirably well there. I have the 5240 CD player at the cabin as well and just the other day picked up a 701, 6220 tape deck and the 5355e CD player. Those 3 were the cheapest yet and 2 of them I have already made to work perfectly. I just have to find that laser for the 5355e...

In addition to that I have repaired some other NAD stuff for friends. So anyway, what I am trying to say is I will follow this with interest. :)

Montycat,

I appreciate your interest. I am on vacation at the moment, but I'll update as soon as possible. I am glad others enjoy working on NAD. I consider them more of a challenge than a pain.

Chris
 
Just saying, as they seem to have a rep of failure. Might want to look into getting suitable replacements before they are unobtatium.


ryuuoh,

I thought about it. But at certain point, those cheap, thin, tactile and pushbutton switches add character to the unit, IMHO.

Chris
 
I'm interested too as I'm working on one. It has a blown channel, both drivers and outputs shorted. I think someone tried replacing the fuses a few times just for good order. New transistors on the way, everythiung else looks ok
 
part numbers

I'm interested too as I'm working on one. It has a blown channel, both drivers and outputs shorted. I think someone tried replacing the fuses a few times just for good order. New transistors on the way, everything else looks ok

I have the same problem, blown channel- bad transistors. You wouldn't happen to have part numbers or "replacement" part numbers? Thanks

Trying to find a service manual also...
 
Subscribed!

I have one of these units that I would like to donate to a friend in need. The problem is that I smoked it by shorting something with my meter leads while attempting to adjust the bias(probably Q427 next to R471).

Anyway, looking forward to your updates and progress on the restoration. Cheers.
 
VintageNAD said:
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.

Hi Chris,

Some people won't need to know why you are doing this. When I lived back in England, and was looking to upgrade from an old Pioneer amplifier, I listened to the NAD 3240PE (amp-only version of your receiver) at a well-known HiFi shop called Billy Vee Sound Systems in South East London, which is still there to this day. I listened to the 3240 against the cream of the crop of similarly priced British designs, I think there was QED, Arcam, Creek and maybe some others. The way they audition stuff is really great, you provide them with the music, and you sit in a comfy chair while they do all the equipment swapping and disc changing. Both myself and the guy in the shop thought the NAD sounded better than the other amps, on both CD and phono sources.

VintageNAD said:
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...

The 3240 and 7240, and the lower priced models of that era were a lot better than the earlier 3020 models. I think my 3240 is made in Japan, the earlier 3020 were made in Taiwan.

VintageNAD said:
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.

There are actually two sets of supply rails. When the amp senses a big transient, it switches the power amp over to the higher voltage. It's a similar design to Pioneer's Dynamic Power design.

VintageNAD said:
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.

I've always left it switched off. On the 3020s I've rebuilt, I don't bother recapping the soft clipping circuit, in fact, I pull the switch and the rest of the components off the board.

VintageNAD said:
Now that you have a bit of background on the unit, here are some of this projects goals.

All good goals. You might want to consider studying the circuit diagram, and looking for caps in the signal path. Pioneer, Sansui, Kenwood, Sony etc. use low leakage electrolytics in the signal path, usually orange Elnas. These can be replaced with Nichicon KL series (or Panasonic equivalent) which are sometimes available with 10% tolerance. If the capacitance is small enough, you might also want to consider replacing with a stacked film capacitor, but you'll need to check the physical size of it first, anything over 10uF in a film gets a bit big.

VintageNAD said:
NAD coated these boards with flux. Looks like we need to clean off the flux. Best to use a cheap, new toothbrush and some 99% isopropyl alcohol.

I've found proper flux cleaner works well, you can get it from Mouser or Parts Express.

VintageNAD said:
Once we are done cleaning the flux, we reheat all joints and resolder any problem joints. We will replace the small electrolytic capacitor (C601) with a Panasonic FM equivalent.

See comments about about low leakage and film caps. I always add a little fresh solder when reheating old joints. Check to see that connecting wires are actually clean enough to stick. On some of the 3020s I've worked on, the wire would pull right out of the board even though it looked firmly soldered in place.

Looking forward to reading more of your progress. Maybe I'll do my 3240 when time allows? Here are some links on the 3020s I've done if they help at all :

http://www.audiokarma.org/forums/showthread.php?t=460678

http://www.audiokarma.org/forums/showthread.php?t=534006

Lee.
 
I found this thread while looking for info about repairing my 7240pe receiver. Had it since '87 and it produces far superior sound to my other options..except that now my speaker channels crackle and cut out after a while. I'm wondering if there are relatively quick/simple diagnostics that a repair shop would be able to use to find the problem? I would like to say that I have the skills/inclination to rebuild it but I don't. So, I'm looking for some expert advice and this thread seems to have people who should be able to help.

It's generally the left channel that cuts out and it may be related to where the volume level is set, around 9-10:00 o'clock position, with or without the Loudness setting turned on. If I fiddle with the volume, the speaker will re-engage for a while. I did a complete vacuuming of the unit and I thought that cured the problem but the problem came back. I'm suspicious the problem could be with the volume control but don't know enough about the mechanics to do anything but guess.

Any advice whether it's worth the diagnostics and whether this problem can be fixed relatively cheaply or should I get the current model, 725BEE? I like the additional features of the new model but it has no phono input.

Thanks.
 
Just found this thread as I have the same receiver and am getting a static, cutting out noise in the right channel. Bought it recently so am curious if anyone can offer advice if it's practical to repair? I have no inclination to do it myself. OK thanks.
 
Interesting thread that died out. I was given a 7240pe a few years back and just put it on a shelf for a few years before actually hooking it up and checking it out. Very impressive receiver with a very good phone stage! Its now in use,using it to run my Turntable.
 
I really enjoyed the brightness and clarity of the phono stage. I thought my needle was going until I played a cd and realized the NAD was having problems.
 
The NAD 7240 is one of the few receivers I have ever heard that produced that bass. I had a massive Realistic STA-2000 (I think that was the model number) that reached very deep but it was that mushy bass. The 7240 gives me enough bass that I actually need to back off on the loudness switch/bass pot at times, something that has never happened with any other amp or receiver that I've listened to. FM tuning is excellent and although people mention poor build quality, they are not junk and they are not toys. I have found them no more difficult to work on than vintage gear and in some cases much easier to work on (crack open a Yamaha CR-600 or CR-800 and start counting all the parts, scorch marks, brittle wires and solder joints and you'll see what I mean--NOT dissing those units, either--among the best built in the world--but far more complex inside than the 7240 by a country mile). Worth repairing. Incredible, spot-on sound. Easy to use. The NAD 7000 is also superb, and with a remote control to boot!
 
The NAD uses FETS Q201, Q302 for power on/off muting.
The Power amp uses breakers (BK-1 &-2) for overload
protection, not sure exactly how ther work. The amp
also has the soft clipping feature which many(+1) suggest
leaving off.
 
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