Oggioffshore
Active Member
I'll not gonna fry anything yet...
Just some frustration, coz lack of experience
Just some frustration, coz lack of experience
NAD 3400 recap, anyone done the job
- Thread starter Oggioffshore
- Start date
The protection circuit uses IC UPC1237H which controls relays RY001(Set A), RY002(Set B)
and RY003(headphones).
Does the protection LED flash on when the amp goes into standby (expect no).
So I wouldn't tinker with the protection circuit.
RY951 appears to control amp power up, schematic a bit hard to read, it's probably for
remote control power on from standby but need to confirm. Need to work out what controls
this relay, the amp does have a microprocessor so expect that to be involved. Possibly
this micro "detects" a problem and orders power down to prevent serious damage, possibly
a short. So don't interfer with RY951, eg, bypass, you could do some serious damage.
EDIT: The micro appears fairly basic, maybe Pin 23, external interrupt...
and RY003(headphones).
Does the protection LED flash on when the amp goes into standby (expect no).
So I wouldn't tinker with the protection circuit.
RY951 appears to control amp power up, schematic a bit hard to read, it's probably for
remote control power on from standby but need to confirm. Need to work out what controls
this relay, the amp does have a microprocessor so expect that to be involved. Possibly
this micro "detects" a problem and orders power down to prevent serious damage, possibly
a short. So don't interfer with RY951, eg, bypass, you could do some serious damage.
EDIT: The micro appears fairly basic, maybe Pin 23, external interrupt...
Last edited:
Oggioffshore
Active Member
Protection LED not active.
Only stand by Led.
Sometimes it goes low level (LED)
Only stand by Led.
Sometimes it goes low level (LED)
Oggioffshore
Active Member
The 3400 can be turned on by either remote or push button on the front.
Appears that there is a (level related?) problem with the right channel of the power amp (not PE stage). When the fault occurs RY951 (power enable) is released and the amp goes back into standby. Need to look at RY951 control. Try to find time later in day hopefully others will chime in.
The "Low Level" has me a bit confused. Would have thought this was a low level/rumble filter for phono, so this would be in the preamp. Hard to see the connection.
The "Low Level" has me a bit confused. Would have thought this was a low level/rumble filter for phono, so this would be in the preamp. Hard to see the connection.
Oggioffshore
Active Member
Guess other amps, use the term "mute"
It's a function on this 3400 called low level, with led light and a push button for it.
It also power up with low level active.
As a protection function I'll guess.
I have re - routed some wiring, but that shouldn't affect this issue...
But who knows.
It's a function on this 3400 called low level, with led light and a push button for it.
It also power up with low level active.
As a protection function I'll guess.
I have re - routed some wiring, but that shouldn't affect this issue...
But who knows.
Attachments
Oggioffshore
Active Member
Oggioffshore
Active Member
Measured around IC 705.
I'll try measure with signal tomorrow.
To see if anything triggers the low level.
Guess this is a micro controller, with its own program for this amplifier.
Or is it a standard circuit used in several applications Pre programmed...
I'll try measure with signal tomorrow.
To see if anything triggers the low level.
Guess this is a micro controller, with its own program for this amplifier.
Or is it a standard circuit used in several applications Pre programmed...
Attachments
I have a NAD 3155, it has the low level (-20dB) switch, but it is a simple on/off. This 3400 uses some circuitry to set it active at power on by default....that's cool.
The use, for me, gives more range of loudness from the volume control. With the switch off, the volume goes from soft to VERY LOUD quickly.
audiotemp
Super Member
IC 705 is a simple 2x2 analog switch that implements the "low level" function by adding/removing resistors from the circuit.
Difficult to find any time for AK.
Q506 appears to be the relay drive for RY951.
You could monitor the voltage at Q506base (or R530/R531 junction/node)
Expect about 0.65Vdc when relay operating normally. Is the voltage stable
or does it drift low leading to possible dropout? or does it go very low
as a result of an "order" from above... probably from IC401.
Q506 appears to be the relay drive for RY951.
You could monitor the voltage at Q506base (or R530/R531 junction/node)
Expect about 0.65Vdc when relay operating normally. Is the voltage stable
or does it drift low leading to possible dropout? or does it go very low
as a result of an "order" from above... probably from IC401.
Oggioffshore
Active Member
Extract of a post from Ray Gianelli,
https://audiokarma.org/forums/index.php?threads/case-history-nad-3400.864486/
"
When closed, the power switch conducts pulses from the microprocessor to one of its input ports. The processor than outputs a voltage at pin 14 that will turn the amp on. That is shown leaving on J404 to connector J001. J001 has several leads that connect to J002, which then leads to J517. One of them loops through to J518, then 2 leads are taken to J951, which is the power on relay board that turns the amp on:
"
So the order comes from the microprocessor. At least two scenarios, the microprocessor detects/is informed of a serious fault and orders power down or the relay is prematurely released due to tired relay drive or...
EDIT maybe a bad connector somewhere J404, J001, J002, J517. Maybe continuity check with amp powered off/unplugged... from J404 pin 3 (Power) to J951, expect less than 1 ohm.
https://audiokarma.org/forums/index.php?threads/case-history-nad-3400.864486/
"
When closed, the power switch conducts pulses from the microprocessor to one of its input ports. The processor than outputs a voltage at pin 14 that will turn the amp on. That is shown leaving on J404 to connector J001. J001 has several leads that connect to J002, which then leads to J517. One of them loops through to J518, then 2 leads are taken to J951, which is the power on relay board that turns the amp on:
"
So the order comes from the microprocessor. At least two scenarios, the microprocessor detects/is informed of a serious fault and orders power down or the relay is prematurely released due to tired relay drive or...
EDIT maybe a bad connector somewhere J404, J001, J002, J517. Maybe continuity check with amp powered off/unplugged... from J404 pin 3 (Power) to J951, expect less than 1 ohm.
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Oggioffshore
Active Member
Oggioffshore
Active Member
I'll see..
My though was, since it turns off, and i hear the relay clicks.
It obviously loose its holding voltage.
I'm curious if the controller get a "stop" signal that triggers the relay, or if it's from somewhere else...
But I'll try that first
My though was, since it turns off, and i hear the relay clicks.
It obviously loose its holding voltage.
I'm curious if the controller get a "stop" signal that triggers the relay, or if it's from somewhere else...
But I'll try that first
Oggioffshore
Active Member
J404 pin 3 has 5 volt when on.
Q506. Collector, has 14 volt when off, and 0,7 when on.
Q506. Collector, has 14 volt when off, and 0,7 when on.
Oggioffshore
Active Member
I have another working amp.
So I'm thinking of switch over the controller pcby, and see if anything changes...
So I'm thinking of switch over the controller pcby, and see if anything changes...
