NAD 3240 PE issues

[baldrick]

Hi guys.

I have this NAD 3240 PE integrated amp on my bench that has a bad right channel.

Original symptom - blew F-502 at the power supply and R466 failed open on the 71 volt rail.
Replaced those components and blew F-502 again. Very high offset in the right channel - like 30 volts at the speaker terminals.

Found also Q424 bad - it's a 2SD669 - obsolete, so substituted in a MJE344.

On turn on, blew F-502 and overheated and blew R466 at the same time. Did not damage Q423.

Looking for ideas on where to start with this. Hoping that one of the output transistors isn't gone as they're obsolete also.

Schematic attached.
Thanks!

 

[baldrick]

I have also noticed that there are some errors in this schematic.
The right channel makes no sense as R465 in the left channel is directly connected to the collector of Q417 and in the right channel R466, it is not connected to Q418.

This is clearly an error and another version of the service manual (a much dirtier copy) confirms this. So perhaps it is not just Q424 the issue, but could also be Q418.

I will check that later today.

 

[tiefbassuebertr]

Obviously there are different versions of this model. Currently I have on the desk two different versions - one device "Made in Singapore" and a second device "Made in Taiwan". Check out the attached files:
Are there even different schematics available ?

 

[tiefbassuebertr]

The device "Made in Singapore" is in working condition, but to avoid excessive overheating in the future (like on the images in my previous post) I replace the mentioned resistors from the names of the attached images by other versions with long silver wires and large distances from the PCB.
The replaced resistors (4x8K2) from the first both images belong to the soft clipping unit between the power amp input and Q401/405 resp. Q403/Q407.
Are therefore anywhere a circuit description available ?

 

[tiefbassuebertr]

Here a line-up of all threads to NAD models 3240PE/7240PE (last model same but incl. FM tuner) I found here on diyaudio:

https://www.diyaudio.com/community/threads/nad-3240-pe-issues.333339/https://www.diyaudio.com/community/threads/nad3240pe-nightmare.364116/
https://www.diyaudio.com/community/threads/another-nad-3240pe-mystery.382646/https://www.diyaudio.com/community/threads/nad-3240pe.18295/https://www.diyaudio.com/community/threads/diy-includes-repair-nad-3240pe-advice-needed.256520/https://www.diyaudio.com/community/threads/nad-3240pe-purchase-dangerous.373165/https://www.diyaudio.com/community/threads/nad-3240pe-potentiometer.367450/https://www.diyaudio.com/community/...s-70-3v-dc-on-output-of-right-channel.377457/ (question post #15)
https://www.diyaudio.com/community/threads/crackling-on-nad-3240pe-power-amp.378818/https://www.diyaudio.com/community/threads/nad-3240pe-amplifier.69014/https://www.diyaudio.com/community/threads/nad-3240pe-high-terminal-voltage.381582/https://www.diyaudio.com/community/threads/nad-3240pe-very-weak-right-channel.115437/https://www.diyaudio.com/community/threads/looking-for-nad-3240pe-schematics.65772/https://www.diyaudio.com/community/threads/nad-power-envelope.377320/https://www.diyaudio.com/community/threads/nad3240-no-bias-current-on-one-channel.379904/https://www.diyaudio.com/community/threads/nad-3240-bad-contact-or-something-else.150424/https://www.diyaudio.com/community/threads/nad-3240-short.358058/https://www.diyaudio.com/community/...reo-amplifier-blows-fuses-immediately.213770/https://www.diyaudio.com/community/threads/nad-7240pe-all-output-transistors-failed.297501/https://www.diyaudio.com/community/threads/nad-7240-pe-state-of-this.375358/https://www.diyaudio.com/community/threads/nad-7240pe-questions.228950/https://www.diyaudio.com/community/threads/nad-7240pe.57767/https://www.diyaudio.com/community/threads/nad-7240pe-damaged-amp-section.151774/

 

[tiefbassuebertr]

I have also noticed that there are some errors in this schematic.
The right channel makes no sense as R465 in the left channel is directly connected to the collector of Q417 and in the right channel R466, it is not connected to Q418.

This is clearly an error and another version of the service manual (a much dirtier copy) confirms this. So perhaps it is not just Q424 the issue, but could also be Q418.

I will check that later today.

check out post #67 with different schematic versions under
https://www.diyaudio.com/community/...repair-nad-3240pe-advice-needed.256520/page-3

 

[poundy]

Obviously there are different versions of this model. Currently I have on the desk two different versions - one device "Made in Singapore" and a second device "Made in Taiwan". Check out the attached files:
Are there even different schematics available ?

not sure where you got this from but they never looked like that new, nor have i ever had one that looked like this.It has had some serious messing about done, all those make do series resistor set ups
I would suspect its failed as a result of poor workmanship.This is what they should look like

 

[tiefbassuebertr]

not sure where you got this from but they never looked like that new, nor have i ever had one that looked like this.It has had some serious messing about done, all those make do series resistor set ups
I would suspect its failed as a result of poor workmanship.This is what they should look like

I have two different service manuals and one device of this model for repair on the desk, which is different again to both service manuals - go for details to post #67 and #68 under
https://www.diyaudio.com/community/...repair-nad-3240pe-advice-needed.256520/page-4
your attached image looks like a device in perfect condition - maybe due an improvement in circuit design (green PCB I haven't see before) - I think it's more likely, however, that the image was taken of a device that has played very little (i. e. few operating hours) and thus it appears in visual new condition.
Please upload an image from the sticker of rear panel from the device showed in your post - thank you very much.

 

[poundy]

All the units I've had through my door have been the same and never varied from the scheme I posted the one you have has had some seriously bad work done on it at dome point. I don't have that one anymore I'm afraid as I sold it

 

[Ian Finch]

If only considering products that were sold in the UK, we may be misled as to the wide, confused and confusing range of model numbers applied to these very popular NAD products. 3240 model was indeed manufactured differently for different global markets, like the ubiquitous 3020, over remarkable totals of years in production.

The manufacturer of NAD products was originally Proton in Taiwan but NAD changed to a Singapore located company for later production of several popular models, including this one. Obviously, the methods and styles of assembly would change somewhat in the process of setting up an assembly line in a different country, factory, management, staff and parts sourcing. Pressure to use extreme cost limiting measures would also, I think, have resulted in ongoing, remedial design changes.

For convenience I guess, 2 or more NAD models were often covered by the same service manual but unfortunately, some still don't match with what was in front of you, as Tiefbassubertrauer discovered. Just look at the various manuals out there for models that share a similar schematic to 3240PE. There are actually a few but they aren't all exactly the same, depending on date of issue, match between the original product distributors location, the product design itself and the appropriate service manual's distribution.

Having quick and easy internet access to service manuals is great but with no document control system, we only have our own mistakes to correct the fundamental one of bad info. Few products ever remain the same from startup to final runout so take care with relevance to your region, date and source of the info.

 

[poundy]

good point realy about models sold in the uk, but if they were all manufactured in the same country wouldnt they be pretty much the same,just with different power supply requirments/ changes?

The models were manufactured all over the place

some examples:
3240/3220pe-primarily singapore
3130-primarily taiwan
3030e-primarily Taiwan
3020i-primarily china
3020 ser 20/A/B-primarily Taiwan
3030-primarily taiwan

and so on and so on

I think the point i was mainly trying to make was that tiefbassuebertr's amp was a bit of a mess due to others interventions, and this may be contributory to why it doesnt match the drawings

but all good points 👍

 

[huggygood]

I kept five 3240 (for the day when I would have the time and the desire to take care of it) of which only one still works and of the five, I have three different color and quality of PCB (brown, green ,blue) .
I have never considered the two diagrams but knowing nad, there is a good chance that there are several variants
and they did the same thing at Proton...