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NAD 3150
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Old 26th September 2021, 09:10 AM   #11
poundy is offline poundy  United Kingdom
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Quote:
Originally Posted by mbz View Post
Vaguely recall there was a service bulletin or similiar where they had reports of relay drop outs. The fix called for adding a resistor on the solder side of the board possibly in parallel with R676? Resistor in parallel with the (flyback) diode seems odd.
edit: not a huge fan of the 3150, reworked 2 units, they only sounded ok. Tones,pace were ok but soundstage was miserable...
actualy other than the series 20-3020 ive not found any other NAD ive worked on that comes up to the standard of the 3240PE or the 3130 which are both great sounding amps
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Old 26th September 2021, 09:36 AM   #12
Mooly is offline Mooly  United Kingdom
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It sounds like the adjustment is working if the bulb increases in brightness.

Just measure voltage across the emitter resistors in the normal way to start with. It has to be working.
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Old 26th September 2021, 11:27 AM   #13
poundy is offline poundy  United Kingdom
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i understand what you are saying, but in my mind is still the question, why is it sitting at zero when i try and adjust
it should be between 4.4 and 11mv but it doesnt move off zero at all on both channels so there must be a common problem right? just where i have to find it.


the emitter resistors you refer to are R659/660?
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Old 26th September 2021, 12:02 PM   #14
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Quote:
Originally Posted by Mooly View Post
It sounds like the adjustment is working if the bulb increases in brightness.

Just measure voltage across the emitter resistors in the normal way to start with. It has to be working.

ok so i think i might be getting somewhere here
i think the left channel is ok,it says to let it warm up for 5 mins and i proberbly didnt first time around ,but the left channel adjusts up ok so set at 8mv and centre is 0v


right channel is at -11mv(closest i can get) so i think the issue is with the right channel and thats where im going to concentrate my efforts starting with the voltages from the beguining
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Old 26th September 2021, 05:20 PM   #15
poundy is offline poundy  United Kingdom
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R851 was dud
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Old 26th September 2021, 05:22 PM   #16
poundy is offline poundy  United Kingdom
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is this an issue not being 0v?


the centre voltage reads 0v weird when done as instructed
Attached Images
File Type: jpg 3150 output stage right grounding.jpg (280.8 KB, 51 views)
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Old 26th September 2021, 06:26 PM   #17
Mooly is offline Mooly  United Kingdom
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For the centre voltage it is the voltage across the speaker terminals that is the one that matters.

If you have zero volts done that way and then you measure from chassis ground and see -66mv at the output then that is probably because of slightly different ground potentials within the amp which is not normally a problem.

(If all grounds were absolutely all the same and had zero resistance between them then we would not have all the problems we see with ground loops and hum and buzzing. So we have to work around them and create 'local' grounds relevant to the circuitry in that area. It is common in digital stuff like CD players to see analogue ground, digital ground and perhaps a separate ground for the motors. They all seem to connect together but the way they do is critical to get low noise because of small voltages and circulating currents)
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Old 26th September 2021, 06:42 PM   #18
poundy is offline poundy  United Kingdom
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its just the idle
something is just niggling at me because i cant adjust it and if you try to adjust it the lamplights up realy bright, and its always on, dim but always on


ive checked all the voltages, right from the power supply, replaced that resistor that was open circuit, and the rest of the voltages seem ok, and yet i just dont think its right


i certainly wouldnt want top plug it into speakers as it is.
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Old 26th September 2021, 07:53 PM   #19
Mooly is offline Mooly  United Kingdom
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Lets start at the beginning... it gets a bit confusing what is going on you see

1/ The centre voltage adjusts OK to zero volts as measured at the speaker terminals. Yes?

2/ The idle current doesn't register as altering on the meter and yet the bulb goes brighter or dimmer as you turn the preset. Yes?

If those two are a 'yes' then connect your meter across either of the 0.22 ohm and with the preset turned to make the bulb at its dimmest measure and record the voltage across the resistor.

What is it?

Now turn the preset so the bulb is brighter and measure the voltage again.

What is it?

Also silly question... I'm assuming the speaker relay is closing correctly and you really are measuring the true DC offset and not just some floaty value because the relay is open.
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Old 26th September 2021, 08:12 PM   #20
poundy is offline poundy  United Kingdom
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1/ The centre voltage adjusts OK to zero volts as measured at the speaker terminals.

2/ The idle current doesn't register as altering on the meter and yet the bulb goes brighter or dimmer as you turn the preset.


yes to both above


i do this in the morning and get back to you


thanks
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