Ciao a tutti, sono un nuovo utente.
il mio NAd 3266 entra in modalità protezione dopo circa un minuto.
Cerco aiuto per ripararlo, ho fatto vari controlli e misurazioni.
Il problema è sul canale sinistro, la resistenza R483 si scalda troppo e se provo a regolare la corrente di riposo con VR103 tra TP1 e TP2 non si muove, rimane ad un valore intorno ai 5 volt.
Quando lo spengo sento un rumore tipo scarica sugli altoparlanti, pensavo fosse un condensatore che perde ma sono buoni, almeno quelli sulla catena del canale sinistro.
I transistor sembrano buoni, ho invertito anche i finali e il problema rimane.
Allego lo schema.
Qualcuno può aiutarmi?
Translation:
Hi everyone, I'm a new user.
my NAd 3266 goes into protection mode after about a minute.
I'm looking for help to repair it, I've done various checks and measurements.
The problem is on the left channel, the resistor R483 heats up too much and if I try to adjust the quiescent current with VR103 between TP1 and TP2 it doesn't move, it remains at a value around 5 volts.
When I turn it off I hear a discharge noise on the speakers, I thought it was a leaky capacitor but they are good, at least the ones on the left channel chain.
The transistors seem good, I also reversed the finals and the problem remains.
I attach the diagram.
Can someone help me?
il mio NAd 3266 entra in modalità protezione dopo circa un minuto.
Cerco aiuto per ripararlo, ho fatto vari controlli e misurazioni.
Il problema è sul canale sinistro, la resistenza R483 si scalda troppo e se provo a regolare la corrente di riposo con VR103 tra TP1 e TP2 non si muove, rimane ad un valore intorno ai 5 volt.
Quando lo spengo sento un rumore tipo scarica sugli altoparlanti, pensavo fosse un condensatore che perde ma sono buoni, almeno quelli sulla catena del canale sinistro.
I transistor sembrano buoni, ho invertito anche i finali e il problema rimane.
Allego lo schema.
Qualcuno può aiutarmi?
Translation:Hi everyone, I'm a new user.
my NAd 3266 goes into protection mode after about a minute.
I'm looking for help to repair it, I've done various checks and measurements.
The problem is on the left channel, the resistor R483 heats up too much and if I try to adjust the quiescent current with VR103 between TP1 and TP2 it doesn't move, it remains at a value around 5 volts.
When I turn it off I hear a discharge noise on the speakers, I thought it was a leaky capacitor but they are good, at least the ones on the left channel chain.
The transistors seem good, I also reversed the finals and the problem remains.
I attach the diagram.
Can someone help me?
Attachments
Welcome to the forum!
I'm attaching the entire manual for anyone wanting to offer advice.
The hot R483 suggests that the amp output is stuck at a supply rail, so I suggest checking amp output voltage before the protection relay. The bias spreader may be involved since you mentioned VR103 was unresponsive and you observe that excessive voltage across the emitter resistors R239 and R240--- 5V!
I infer that the amp may recover after resetting since you mention protection occurs after about a minute. This surprises me, as I would have expected the damage was catastrophic.
I normally enjoy troubleshooting amps, but the design of this amp leaves me unnerved. I hope other members will jump in.
Good luck!
I'm attaching the entire manual for anyone wanting to offer advice.
The hot R483 suggests that the amp output is stuck at a supply rail, so I suggest checking amp output voltage before the protection relay. The bias spreader may be involved since you mentioned VR103 was unresponsive and you observe that excessive voltage across the emitter resistors R239 and R240--- 5V!
I infer that the amp may recover after resetting since you mention protection occurs after about a minute. This surprises me, as I would have expected the damage was catastrophic.
I normally enjoy troubleshooting amps, but the design of this amp leaves me unnerved. I hope other members will jump in.
Good luck!
Hello, the output voltage on the left channel is 1.5 volts the right 0.
If you turn off the power to the left channel it works, when the attack goes into protection.
If I put a lamp in series on the 220 volt cable it works well and does not go into protection, but 1.5 volts remain on the left channel output.
On the control of the U102 operational amplifier which deals with the resetting of the offset of the left channel I find fluctuating values on pins 2 and 3 that vary between -3v and 1.5v ????????.
on the other pins:
4 -17,8v
5-17,8v
6 0v
7+18,6
8 0v
If you turn off the power to the left channel it works, when the attack goes into protection.
If I put a lamp in series on the 220 volt cable it works well and does not go into protection, but 1.5 volts remain on the left channel output.
On the control of the U102 operational amplifier which deals with the resetting of the offset of the left channel I find fluctuating values on pins 2 and 3 that vary between -3v and 1.5v ????????.
on the other pins:
4 -17,8v
5-17,8v
6 0v
7+18,6
8 0v
Last edited by a moderator:
Hard to imagine 0V on opamp pin 6, especially with moving voltage on pin 2 that can come only via pin 6. Sure sounds like a bad opamp, though it would be a pleasant surprise if that's the only problem.
I think I'd double check readings, then replace. And install a IC if there isn't one already there.
Good luck!
I think I'd double check readings, then replace. And install a IC if there isn't one already there.
Good luck!
That should have been "IC socket."
What was the amp ouput voltage when R483 was hot?
You mentioned a light bulb lowered the mains. Would report resulting AC supply voltage and resulting DC rail voltages?
Thanks.
What was the amp ouput voltage when R483 was hot?
You mentioned a light bulb lowered the mains. Would report resulting AC supply voltage and resulting DC rail voltages?
Thanks.
Hi, I found a desoldered jumper. Now I was able to adjust the quiescent current.
The two operational amplifiers U102 and U302 have the same measurements therefore they work.
The problem of 1.5 volts on the left channel output remains.
I can't figure out what causes it.
The two operational amplifiers U102 and U302 have the same measurements therefore they work.
The problem of 1.5 volts on the left channel output remains.
I can't figure out what causes it.
If left channel is at 1.5V, I would expect U102A pin 6 to be stuck near its positive supply rail.
If the servos are working properly, their output (pin 6) voltages should be in the active region, well clear of both rails.
What do they measure?
If the servos are working properly, their output (pin 6) voltages should be in the active region, well clear of both rails.
What do they measure?
Some tests:
1-I turned it on with the Variac at 140 and it works well, the power supply of the two channels taken at the output of the J602A and J603A power supply board measures +27v and -27V.
2-with the Variac increasing the voltage up to 220v the measurement on J602A and J603A goes from + and - 27V to + and - 47v and the protection is triggered.
3-turned on only by connecting the right channel (the good one), the measurement on J603A is + and - 36.6V and works well.
4- if I turn it on with the Variac set to 220v it sounds soft and croaky but going down to 150 the right channel is connected and at 140v the left is also connected and the measurement on J602A and J603A goes from + and - 47V to + and - 27V
1-I turned it on with the Variac at 140 and it works well, the power supply of the two channels taken at the output of the J602A and J603A power supply board measures +27v and -27V.
2-with the Variac increasing the voltage up to 220v the measurement on J602A and J603A goes from + and - 27V to + and - 47v and the protection is triggered.
3-turned on only by connecting the right channel (the good one), the measurement on J603A is + and - 36.6V and works well.
4- if I turn it on with the Variac set to 220v it sounds soft and croaky but going down to 150 the right channel is connected and at 140v the left is also connected and the measurement on J602A and J603A goes from + and - 47V to + and - 27V