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NAD 3150
NAD 3150
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Old 25th September 2021, 11:45 AM   #1
poundy is offline poundy  United Kingdom
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NAD 3150
Default NAD 3150

moved on to this for now while i wait for the parts for 3140


report that came ti this is.
powers on ok one channel ok
other channel sound in and out


so ill have a look at this one
update


problem is i cannot find TP1 or TP2 which i presume means test points and they are supposed to be on the underside of the board, bit i cant find them for love nor money


maybe someone on here has had the same issue and knows where they are?

Last edited by poundy; 25th September 2021 at 12:29 PM.
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Old 25th September 2021, 12:53 PM   #2
poundy is offline poundy  United Kingdom
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ok for those who may need to find in the future tp1 and 2 are ontop of the large white resitors
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Old 25th September 2021, 03:20 PM   #3
poundy is offline poundy  United Kingdom
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managed to set the centre ok but the idle current adjustment doent work on either channel so ive got to try and find out why
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Old 25th September 2021, 04:06 PM   #4
poundy is offline poundy  United Kingdom
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someone has put a 1k resistor in parellel with D615, why would they have done that doyou think? it wasnt fitted as standard and you can tell it was done after as it was badly fitted
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Old 25th September 2021, 05:11 PM   #5
Mooly is offline Mooly  United Kingdom
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NAD 3150
D615, so the one across the relay.

Adding a resistor will alter the voltage across the relay coil but I can't say by how much without knowing the ohms of the coil alone. Its easy to work out, the 1k and the relay are effectively a single resistor in series with the 680 ohm. So if you know the supply voltage and assuming pin 6 goes down to zero volts you can easily work the voltage out

The resistor can only lower the voltage and there are much better ways of doing that also save power, not increase it like a resistor.
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Old 25th September 2021, 05:26 PM   #6
poundy is offline poundy  United Kingdom
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but why do it in the first place?


the lamp is on with this one but dim so i cant see much being wrong with this one.



i cant seem to adust the idle as per the tech spec, but ill work on that tomorrow.
i replaced the 2 no 100ohm trimmers with new ones as the others were a bit crappy.

Last edited by poundy; 25th September 2021 at 05:32 PM.
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Old 25th September 2021, 05:33 PM   #7
Mooly is offline Mooly  United Kingdom
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No idea. Can you be certain it is not a factory afterthought mod... it happens.

Relay coils will often work well on lower than the stated voltage and doing that reduces how hot they get.

Ideally the relay should snap in smartly with full voltage and then the voltage reduce to a holding value... which is easy to do with a cap. The cap is charged to the full supply voltage and then when the chip turns the relay on there is full voltage available for an fraction of a second. After that a series resistor limits current and the voltage falls. A 24 volt relay coil will 'hold' down to about 6 volts but it will not pull in with a low voltage.

A series Zener is often useful for dropping excess voltage rather than a resistor.
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Old 25th September 2021, 07:47 PM   #8
maudio is offline maudio  Netherlands
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I own one, for over 30 years now. Still in use as a power amp for my subs. Nice amp, recently recapped it and that made a world of difference. It broke down a few times, every time because plain high value resistors failed or had significant changed resistance. Probably they did not use the best batch back then. Not the kind of component that usually fails so be aware.... I had 22k resistors that measured 15k and 18k that measured over 30. Carefully check all voltages in the entire amp and investigate any deviations.
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Old 26th September 2021, 03:25 AM   #9
mbz is offline mbz  Australia
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Quote:
Originally Posted by poundy View Post
someone has put a 1k resistor in parellel with D615, why would they have done that doyou think? it wasnt fitted as standard and you can tell it was done after as it was badly fitted
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...

Last edited by mbz; 26th September 2021 at 03:27 AM. Reason: edit
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Old 26th September 2021, 08:09 AM   #10
poundy is offline poundy  United Kingdom
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Quote:
Originally Posted by Mooly View Post
No idea. Can you be certain it is not a factory afterthought mod... it happens.

Relay coils will often work well on lower than the stated voltage and doing that reduces how hot they get.

Ideally the relay should snap in smartly with full voltage and then the voltage reduce to a holding value... which is easy to do with a cap. The cap is charged to the full supply voltage and then when the chip turns the relay on there is full voltage available for an fraction of a second. After that a series resistor limits current and the voltage falls. A 24 volt relay coil will 'hold' down to about 6 volts but it will not pull in with a low voltage.

A series Zener is often useful for dropping excess voltage rather than a resistor.

main issue at the moment is i cant alter the idle current.
when i do it as per the instructions there is no movement on the meter at all, as i turn the pots the lamp just gets brighter or dimmer, i guess as the current is increased, but no change in the meter readings.
worked ok doing the centre no problem so nothing wrong with the test points ,or the pots as they are new ones.
going to start having a look at this a bit later after ive been out for a nice long walk
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