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NAD 2200PE DC Voltage Spike on Power Off

M

mohare134

New Member
Hello Forum,
I posted this to an old forum that didn't get any traction, so I'm posting new.
I have a NAD 2200PE that works just fine (kinda). I also tested the tp voltages and they are fine too. I adjusted the DC offset and idle voltages to within parameters. This unit did need new speaker protection relay's which I replaced.
Problem is, when I turn the unit off (either by power switch or by unplugging) I get a DC voltage spike measured at about 74Vdc (with VoM)...obviously the speakers don't like that...and it hits just before the relay circuit breaks the speaker connection.
This happens identically on both channels (even with no input source).
Any ideas on what could be causing that?
 
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Suggests that the negative power rail is collapsing immediately at power off. Have you replaced any caps, eg the mains?
Will take a look at the sm so hopefully will add something helpful
 
mbz said:
Suggests that the negative power rail is collapsing immediately at power off. Have you replaced any caps, eg the mains?
Will take a look at the sm so hopefully will add something helpful
Click to expand...
I have not yet...That was my next endeavor...but wanted to wait for some insight.
 
The theory/guess is one of the main caps is in poor condition so
the power rail collapses immediatelty at p-off. Need to monitor the
power rails to test theory, ideally will need 2 multimeters but can
get by with one. A connection block and minnigrabbers would also be
helpful.

First need to monitor the voltages at the outer pins (1&8) of JP201.
Monitor the dc voltage at each pin during power off.

Repeat for pins 2&7

Hopefully one of the pins (negative rail?) will be significantly less
than the other.

upload_2019-5-4_14-6-3.png
 
IMO just order the mains caps.. sure check the soldering first..get your magnifying glass out. Nads are known for bad caps and soldering. Might as well do it right and recap it all and reflow. Ain't getting any younger. :D
 
Sorry for the delay...can only play with my toys in the evening ;)
So here are the readings:
Pins 1/8=220Vdc when amp is activated (no signal)
Pins 2/7=143Vdc

Hooking up a test speaker and turning the unit off (thump), these are the values taken immediately after the thump (when unit is off)
Pins 1/8=70Vdc (and falling)
PIns 2/7=108Vdc (and falling)

With the test speaker attached. I placed the VoM leads on the test points DURING power off and these were my values:
Pins 1/8= Immediate drop to 180Vdc
Pins2/7= Slow decline from 143Vdc

So, it looks like either C411 or C412 is losing their shi** during power off...
Replace all 4 main power caps, right?
 
Last edited:
Wanted voltage measurements between each pin and ground/chassis, apologies for confusion., looks like
you measured between pins. Also no need to connect speakers, may do damage.

Looks like pins 1 and 8 are +/-110Vdc when powered up, seems a bit high
Pins 2&7 are +/-72Vdc

At power off pin 1&8 appears to collapse very quickly.

As per @Binkman above, NADs generally used cheap caps, they are long overdue.
Rather than spend time troubleshooting I'd be tempted to replace the 4 caps knowing
the problem may be due to other causes.
 
@mbz & @Binkman
Thanks for the clarification. I can check each pin individually just for kicks...though now it is obvious the voltage is dropping like a stone. I ordered new caps last night...like others have mentioned, you can't find these 120V 10,000uf caps...must have been NAD customs. I had to go with some un-branded China models at 125V labeled "perfect for 120V audio applications"- sounds like they know something we don't ;)
Regarding the voltage, they're both actually high...C411/412 are both on the +/-95V rail and C413/414 are on the +/-62V rail. This is because the power coming out of my outlet is high...frankly too high for me taste.

Add-on, I tested the caps as directed...C411 is the one losing it's voltage. Drops from 109V to 73V immediately.
I had to attach a test speaker because otherwise, there is no load to draw the power...I tried it without my crappy speaker attached and it didn't drop the voltage...guess you can use a shunt too....
 
Please don't buy caps, transistors on ebay, they are likely
to be fakes, cr@p and over priced. Plenty of reliable sources
about (Mouser, Digikey,,,)


This probably indicates that C411 is not the problem. I'm thinking
that either Q314 or Q318 is staying ON possibly due to a low Vbe
or the control (Q310, Q306 and Q302) is slow to shut down.
Troubleshooting this would be painful, suggest replace the caps
(C411,,,) first.

Maybe diode test Q314 and Q318 noting Vbe
 
I agree about the caps, but try and find a 120V, 125V or even a 150V 10,000uf cap that either exists or fits the unit is hard (almost impossible) to come by...I read where folks have to create their own daughter board to use what's available today.
Regarding the Vbe...remember, this is on both channels, not just the right.
I'll replace the main power caps and let you know how it goes...might take a while to get here though...
 
Hello All.
It's been while but I finally fixed the unit. It's been on the shelf for a while as I was waiting for the new Chinese caps...they came and didn't fix the problem, so I had to dig deeper.
It wound up being the protection IC not releasing the relay coils fast enough...when I turned the unit off, there was about 1/2 second delay and that is when the thump happened.
Checking the voltages on the protection IC, they were off from what I researched online...bought a new one and dropped it in and now there is no more thump!

Thanks again for all of the advice!
 
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