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NAD 3225PE restoration [lots of pics]

post #1 of 7
7/29/08 at 6:46pm
Thread Starter 
Over in the ortho thread, dBel84 kindly offered to guide me in attempting to repair my ageing NAD 3225PE, which went up in smoke a few years ago. I'm a total noob at DIY and have only modest soldering skills (but I'm reading “The Art of Electronics” so sometimes in the next decade I will have a slight understanding of what's going on), so things should get interesting pretty fast.

The saga starts with some pics, the schematics first followed by the naked NAD with the impact area exposed. High resolution shots are available by clicking on the pics.




The beast, naked.


The impact area.


A different angle of the same area.


Enlargement of a different area.
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post #2 of 7
7/29/08 at 7:13pm
Hey,

I'm no NAD expert but that looks like maybe mid- to late 80s gear there. Not sure its worth too much fooling around or $$s to repair UNLESS this is for fun, learning & possible gratification of doing it yourself

Caught my eye because I repaired a NAD 210 or 310 or somesuch that I got off ebay for like $50 delivered... Turned out it was the PS caps... Been working great daily ever since.

Anyway, it *looks* to me like a blown up tantalum, but you have to try to rub off some of the burn & see if you can get the component # to match up w/the schematic... Might be able to localize it by following a route in the schematic from an identifiable component connected (by traces) to the blown one.

Often, something upstream or downstream of the blown component is the real problem, so just replacing the burnt ones can lead to them burning again.

And anything on the order of 20yrs old probably needs most, if not all, electrolytic caps replaced (I'd start with the Power Supply).

Anyway, maybe just IDing the burnt component(s) & replacing them could get you somewhere... Post back with the parts & values and if they are cheap & plentiful someone here might have them laying around.

Good luck.

N.B. This might be better posted to Audiokarma's Vintage SS forum More applicable & you might get better focused help (& more of it?)
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post #3 of 7
7/30/08 at 12:49am
it doesn't look very good I'm afraid.

That splodge is or at least was a resistor (R454) connecting the bases of the 2 large output BJT's on the left channel. This does not bode well for downstream effects when such large currents run rampant through the circuitry.

..dB
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post #4 of 7
7/30/08 at 3:28am
Thread Starter 
Quote:
Originally Posted by dBel84 View Post
it doesn't look very good I'm afraid.

That splodge is or at least was a resistor (R454) connecting the bases of the 2 large output BJT's on the left channel. This does not bode well for downstream effects when such large currents run rampant through the circuitry.

..dB
I told you it was a mess.

So it's scrapyard time?
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post #5 of 7
12/4/08 at 8:24pm
Hi,

I too have a NAD 3225PE, which has worked beautifully for years. right up until yesterday.

its my own fault - i was messing with the speakers with the amp running, and shorted the speaker wires on one channel, resulting in a 'pop' and a burning smell.

opened it up to find R512 an obvious charred mess, and a bit more looking revealed R438 also toasted.

i found this thread while looking for a circuit diagram. I'll start by replacing these parts (found their values from the circuit diagram link) and see if that fixes it. however, in my amp, it looks like R512 was two 2W resistors in parallel - wondering if this means it is different from the standard circuit. Ludoo, do you think you could have a peek at yours and see if yours is the same, and if so, what the value of the parallel resistors are? R512 is over on the right side, hidden by the black ribbon cable in your pics above

R512 is in the power supply, and R438 seems to be in the input stage. I'd love some advice on what else i might need to replace that might have died less obviously.

cheers,

Ben

cheers,

ben
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post #6 of 7
12/5/08 at 12:22am
replaced the two diodes, and a couple of nearby caps that looked scorched. power up. no good. sacrificial speaker produces loud hum, and R438 heats up very fast... was on for less than a second and it was too hot to touch.
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post #7 of 7
11/18/10 at 5:41am

Hi there,

 

I know this is an old thread, but I used the schematic to repair the exact same amplifier which had the exact same components that were burnt as the original poster.

May have been the other channel but they are the same.

 

I tested with a multimeter and removed components and tested, basically until there was no shortcircuit.

I check all the other transistors on the channel and once I had replaced the components I also made sure the circuits were similar by measuring across transistors etc on each channel.

 

Components that were broken and replaced:

 

Q415  -  2N3055

Q417  -  MJ2955

Q411  -  2SD669A

Q413  -  2SB649A

Q409  -  BD139

R453  -  180ohm

C431  -  0.1uF I think

The four 4A fuses on the power supply board

 

I think the fuses blew because when the output transistors failed it shorted the rails.

 

This happened due to a shorted speaker wire and the amp was turned on.

 

Hope this helps someone.

Cheers

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