Hello.
NAD 306 rest in Protect mode.
All fuses are ok.
Any ideas?
Best regards.
SM
NAD 306 SM Service Manual download, schematics, eeprom, repair info for electronics experts
NAD 306 rest in Protect mode.
All fuses are ok.
Any ideas?
Best regards.
SM
NAD 306 SM Service Manual download, schematics, eeprom, repair info for electronics experts
If it immediately goes into protect on power up, then most likely you have DC on the speaker output.
If you can disconnect one channel at a time and power up, if it stays out of protect with one channel and not the other then you know which channel has the issue.
Most likely the issue is a short, start at the outputs and test backwards until you find the failed parts(s).
Pictures of amp and problem area would also help us to provide better assistance.
If you can disconnect one channel at a time and power up, if it stays out of protect with one channel and not the other then you know which channel has the issue.
Most likely the issue is a short, start at the outputs and test backwards until you find the failed parts(s).
Pictures of amp and problem area would also help us to provide better assistance.
R480 can be checked with a DVM. Resistance may be somewhat lower due to leakage through semiconductors. Resistor color code is on wikipedia.
Usually failures are output transistors, which fail back to the drivers, predrivers, input parts due to high voltage coming out of the failed transistors base leads. check output transistors with double diode test b-e b-c on DVM. 450-700 mv forwards, ---- or 9999 backwards. Failed output transistors often burn up the emitter resistors also.
On geriatric units like this, electrolytic caps are suspect. Also mica washers under output transistor, those sometimes short across after 30 years. If replace output transistors, definitely use new mica washer + heat sink compound, or better, silicon rubber heat pad.
People make mistakes. During initial power on tests limit size of fault current with 60 w light bulb series the AC input. I put my light bulb socket in a grounded metal case with a circuit breaker. If the wire falls off the light bulb socket (*****y screws, not secure with stranded wire) the AC wire touches the case & blows the breaker, instead of touching my hand or setting fire to something. I get circuit breakers at surplus houses online. Light bulb base from hardware store.
during power on tests, put negative lead of DVM to speaker ground with alligator clip. Use only one hand at a time, voltage >25 across the heart can stop it. Wear no jewelry on fingers, hands, or neck. 1 V @ 25 amps through a ring can burn your flesh to charcoal. Use safety glasses, parts sometimes explode. Also desoldering, solder splashes.
Usually failures are output transistors, which fail back to the drivers, predrivers, input parts due to high voltage coming out of the failed transistors base leads. check output transistors with double diode test b-e b-c on DVM. 450-700 mv forwards, ---- or 9999 backwards. Failed output transistors often burn up the emitter resistors also.
On geriatric units like this, electrolytic caps are suspect. Also mica washers under output transistor, those sometimes short across after 30 years. If replace output transistors, definitely use new mica washer + heat sink compound, or better, silicon rubber heat pad.
People make mistakes. During initial power on tests limit size of fault current with 60 w light bulb series the AC input. I put my light bulb socket in a grounded metal case with a circuit breaker. If the wire falls off the light bulb socket (*****y screws, not secure with stranded wire) the AC wire touches the case & blows the breaker, instead of touching my hand or setting fire to something. I get circuit breakers at surplus houses online. Light bulb base from hardware store.
during power on tests, put negative lead of DVM to speaker ground with alligator clip. Use only one hand at a time, voltage >25 across the heart can stop it. Wear no jewelry on fingers, hands, or neck. 1 V @ 25 amps through a ring can burn your flesh to charcoal. Use safety glasses, parts sometimes explode. Also desoldering, solder splashes.
Last edited:
I desoldered R480 he is dead.
With new resistor 0.1ohm 2w Amplifier works fine.
Bias ok......7-8mV.
Its a great machine.
The sound is very nice.
I think that the former owner was replaced 2 MOSFET IRFP240 because they are different from the factory transistors.
But it will not replace R480 and abandoned the Amplifier.
Thank you very much,you are the best.
With new resistor 0.1ohm 2w Amplifier works fine.
Bias ok......7-8mV.
Its a great machine.
The sound is very nice.
I think that the former owner was replaced 2 MOSFET IRFP240 because they are different from the factory transistors.
But it will not replace R480 and abandoned the Amplifier.
Thank you very much,you are the best.
Last edited:
I'm glad to hear an incomplete repair by the previous owner or tech was the cause of the problem. Enjoy holiday music, just in time.
Hello all,
I have a Nad 306, bought new years ago and I like the sound it gaves.
But (yes there is a but).
Few weeks ago, my son switch the input selector.
And then a big "bzzzz" sound, and after that, nothing.
"Have you tried to turn it off and on again ?"
Yes I have, unsuccessfully.
Having a look inside, nothing seems to be burn.
Testing the power transistor with a multimeter => all of them seems to be OK.
Checked the idle current => same.
I have not clue on how to start to investigate on this issue.
Seems obvious that the IC 402 (TA7317P) is involved, but how to go ahead ?
I have a Nad 306, bought new years ago and I like the sound it gaves.
But (yes there is a but).
Few weeks ago, my son switch the input selector.
And then a big "bzzzz" sound, and after that, nothing.
"Have you tried to turn it off and on again ?"
Yes I have, unsuccessfully.
Having a look inside, nothing seems to be burn.
Testing the power transistor with a multimeter => all of them seems to be OK.
Checked the idle current => same.
I have not clue on how to start to investigate on this issue.
Seems obvious that the IC 402 (TA7317P) is involved, but how to go ahead ?
Last edited:
With any linear amplifier, start testing with disconnecting signal input and output leads, turn volume down to zero and connect your voltmeter to the output terminals, red to red, black to black. Unless the meter is an autoranging type, set the meter voltage range high (200V) to begin with. This is only a very brief, preliminary test for its general condition. From here we may have to get serious. If there is significant DC voltage across the output terminals, we will have to do just that.
Then power up with a DBT (dim bulb tester) connected between the mains power socket and the amplifier, so further damage is limited to only what the bulb's bright current to the transformer can do. Hopefully, the bulb will flash then settle to a dim glow which will indicate that the amplifier is stable and drawing approximately normal idle current.
So, an incandescent mains rated lightbulb is required and of course, these are now obsolete but enough of the quartz halogen variety remains for the keen DIY to find. You will need a 75-100W type for this larger NAD model and you can Google "dim bulb tester" or "lightbulb limiter" for dozens of posts, sketches and pics of DIY built testers, videos etc. to check what parts you need. Some are cr*p, blurry images or boring details but you can get the idea, even if they were intended for repairing tube/valve type guitar amplifiers.
Be sure to connect all mains wiring with due care, use screw or crimped terminal connections and insulated sleeving over live metal parts. Most important - fit the assembly in an insulated box, like a mains power junction box so that kids and and even you can't receive shocks. There are easier ways too, if you have a spare table lamp that you can re-wire for the purpose.
If you get this far without needing further hints, you are on the way to finding what's wrong and repairing it, assuming the parts or substitutes are still available.
Then power up with a DBT (dim bulb tester) connected between the mains power socket and the amplifier, so further damage is limited to only what the bulb's bright current to the transformer can do. Hopefully, the bulb will flash then settle to a dim glow which will indicate that the amplifier is stable and drawing approximately normal idle current.
So, an incandescent mains rated lightbulb is required and of course, these are now obsolete but enough of the quartz halogen variety remains for the keen DIY to find. You will need a 75-100W type for this larger NAD model and you can Google "dim bulb tester" or "lightbulb limiter" for dozens of posts, sketches and pics of DIY built testers, videos etc. to check what parts you need. Some are cr*p, blurry images or boring details but you can get the idea, even if they were intended for repairing tube/valve type guitar amplifiers.
Be sure to connect all mains wiring with due care, use screw or crimped terminal connections and insulated sleeving over live metal parts. Most important - fit the assembly in an insulated box, like a mains power junction box so that kids and and even you can't receive shocks. There are easier ways too, if you have a spare table lamp that you can re-wire for the purpose.
If you get this far without needing further hints, you are on the way to finding what's wrong and repairing it, assuming the parts or substitutes are still available.
Last edited: