My NAD C300 Amplifier has just lost the Ghost. Output is barely audible on either channel even when the volume is set to maximum. You can just hear the music when you get close to the speakers.
The question is rather open ended but any suggestions on where to start would really help.
I am no expert but thanks to this forum, I managed to repair my old NAD 304 with just a £3 soldering gun and a 10p resistor. I could have gone round in circles but a similar fault had been diagnosed on here.
The question is rather open ended but any suggestions on where to start would really help.
I am no expert but thanks to this forum, I managed to repair my old NAD 304 with just a £3 soldering gun and a 10p resistor. I could have gone round in circles but a similar fault had been diagnosed on here.
NAD C300 OUTPUT VERY FAINT
Unlike the classic NAD Amps where there is clear seperation from PRE Amp to Power Amp this one does not have the facility so its impossible to use it as preamp to see if its only the output thats faulty.
I will open to see if I can make sense of what the problem is . The only tools I have at the moment are a Digital Multimeter and a soldering gun. All suggestions are welcome
Unlike the classic NAD Amps where there is clear seperation from PRE Amp to Power Amp this one does not have the facility so its impossible to use it as preamp to see if its only the output thats faulty.
I will open to see if I can make sense of what the problem is . The only tools I have at the moment are a Digital Multimeter and a soldering gun. All suggestions are welcome
I HAVE NOW OPENED THE NAD C300
I opened the NAD C300 tonight and found that there are 2 x 5AT Fuses on the power supply board and these are blown there is another set of 2 x 0.5A Fuse which are intact. I replaced the 2 blown fuses and switched the AMP on. The 5AT fuses blow straight away but the 2 0.5A are intact and the green LED at the front of the unit still comes on. There are seven cables feeding main PCB from the PSU board near the toroid (six output wires from toroid going to PSU board). I assume there are 2 indepedent voltage rails high and low and its the higher side probably to the power amp where there is a current surge.
Any suggestions?
I opened the NAD C300 tonight and found that there are 2 x 5AT Fuses on the power supply board and these are blown there is another set of 2 x 0.5A Fuse which are intact. I replaced the 2 blown fuses and switched the AMP on. The 5AT fuses blow straight away but the 2 0.5A are intact and the green LED at the front of the unit still comes on. There are seven cables feeding main PCB from the PSU board near the toroid (six output wires from toroid going to PSU board). I assume there are 2 indepedent voltage rails high and low and its the higher side probably to the power amp where there is a current surge.
Any suggestions?
I HAVE FOUND THE FAULT
After searching this site for similar problems on other Amps I drew the conclusion that the MOSFETS were blown. Checking the resistance across the mosfets (suggested on one thread on an ARCAM AMP), a pair on one channel showed very low resistance so I soldered them off. Switching on the amp this time did not blow any fuse, so I proceeded to connect some speakers and one channel now works.
I now need to replace 2 Mosfets, P55NE06L made by ST. A search on google draws a blank. I now think these are called STP55NE06L after an extended search and are now discontinued. Does anyone know if STP55NF06L is compatible?
After searching this site for similar problems on other Amps I drew the conclusion that the MOSFETS were blown. Checking the resistance across the mosfets (suggested on one thread on an ARCAM AMP), a pair on one channel showed very low resistance so I soldered them off. Switching on the amp this time did not blow any fuse, so I proceeded to connect some speakers and one channel now works.
I now need to replace 2 Mosfets, P55NE06L made by ST. A search on google draws a blank. I now think these are called STP55NE06L after an extended search and are now discontinued. Does anyone know if STP55NF06L is compatible?
Hi, I think I'm having exactly the same problem with my C300. I rekon I blew it when instaling some new speakers with too long speaker wire protruding from the sheath. I thought "I'll sort that out later when I know its working", but in the meantime I think they crossed, shorting the speakers and blowing something. Sure enough changed the 5A fuses, blew again, so went searching. (The speakers work just fine with my other amps)
Not had a chance to check the Mosfets but pretty sure it will be the same problem and on one chanel like yours Kajman. Hoping so anyway. Won't be able to have a go at this for at least a week but was wondering if you managed to source the ST mosfets? Like you I can only find the STP55NF06L, and they seem to have a lower resistance (0.018 ohm vs 0.022 I believe) I'm not an electrician but willing to give this a go if I can find something compatible. Have you had any joy?
Not had a chance to check the Mosfets but pretty sure it will be the same problem and on one chanel like yours Kajman. Hoping so anyway. Won't be able to have a go at this for at least a week but was wondering if you managed to source the ST mosfets? Like you I can only find the STP55NF06L, and they seem to have a lower resistance (0.018 ohm vs 0.022 I believe) I'm not an electrician but willing to give this a go if I can find something compatible. Have you had any joy?
I HAVE FIXED IT
Mine is fixed and running fine now. I measured the resistance across the mosfets as explained. I removed the ones from one channel that appeared to have very little resistance across them. I then replaced both the blown fuses and they did not blow this time. I did this just to make sure there were no other components blown with the mosfets
I ordered the STP55NF06L as I could not find the original STP55NE06L. I got them form Dannel.net for about £1.10 each though they sell them in packs of 5. I have replaced them and they work a treat. You will need an allen key to get them out and a green ceramic will have to be soldered off to get the allen key in (Just remember to solder it back in after all this I almost forgot to do it.). You might need to make a couple of adjustments before attempting to connect any speakers even if all appears to be ok. You will have to check the voltages across the speaker connectors with a meter making sure the reading across each channel is less than 10mV. There are 4 white adjusters in the unit 2 are for the Output offset voltage and the other 2 for idling current (I guessed it should be about 5-7mV for the idling current by looking at a NAD 304 Schematic) I had to play around with the adjusters before satisfying myself that it was safe to connect the speakers.
I might sound like an expert but I had no clue as to what to do myself before all this. The unit has been on for 3 days continously now and its running sweetly.
I hope this helps
Mine is fixed and running fine now. I measured the resistance across the mosfets as explained. I removed the ones from one channel that appeared to have very little resistance across them. I then replaced both the blown fuses and they did not blow this time. I did this just to make sure there were no other components blown with the mosfets
I ordered the STP55NF06L as I could not find the original STP55NE06L. I got them form Dannel.net for about £1.10 each though they sell them in packs of 5. I have replaced them and they work a treat. You will need an allen key to get them out and a green ceramic will have to be soldered off to get the allen key in (Just remember to solder it back in after all this I almost forgot to do it.). You might need to make a couple of adjustments before attempting to connect any speakers even if all appears to be ok. You will have to check the voltages across the speaker connectors with a meter making sure the reading across each channel is less than 10mV. There are 4 white adjusters in the unit 2 are for the Output offset voltage and the other 2 for idling current (I guessed it should be about 5-7mV for the idling current by looking at a NAD 304 Schematic) I had to play around with the adjusters before satisfying myself that it was safe to connect the speakers.
I might sound like an expert but I had no clue as to what to do myself before all this. The unit has been on for 3 days continously now and its running sweetly.
I hope this helps
That is brilliant, thanks very much for your help on this one. Next weekend I should get a chance to check that the mosfets are the problem and I will try to make these modifications as suggested.
Really appreciate the help, will post again to let you know how it goes. Would be good to get the old gal up and running again.
Really appreciate the help, will post again to let you know how it goes. Would be good to get the old gal up and running again.
My C300 has the exact same symptoms ...
Hi there Kajman , my amp seems to have the same problem, at least I hope so.
It occurred after shorting the wires at the binding posts while switching between two pairs of speakers.
I've soldered a few times,but in less delicate scenarios. I'm in no way qualified to attempt a repair but I'm willing to give it a try as I have no other options. Really can't afford to pay for any help.
Could you help me determine the location of the MOSFETS so I can attempt replacing them ?
Some basic instructions written or drawn over the attached photo would go a long way for me.
Thanks in advance , I hope you find the time to help me. Cheers !
Hi there Kajman , my amp seems to have the same problem, at least I hope so.
It occurred after shorting the wires at the binding posts while switching between two pairs of speakers.
I've soldered a few times,but in less delicate scenarios. I'm in no way qualified to attempt a repair but I'm willing to give it a try as I have no other options. Really can't afford to pay for any help.
Could you help me determine the location of the MOSFETS so I can attempt replacing them ?
Some basic instructions written or drawn over the attached photo would go a long way for me.
Thanks in advance , I hope you find the time to help me. Cheers !
Attachments
Hm, the internal layout doesnt look like whats described in the C320 service manual!
Check for the blown fuses. If they are blown, it is likely one or all of the output transistors have failed - these are the 4 square devices on the large heatsink to the right of the power transformer. The service manual says these are 2SA1943/2SC5200 (very popular in amplifiers), but your picture suggests they are not. I'd want to see the correct schematic before advising further.
Check for the blown fuses. If they are blown, it is likely one or all of the output transistors have failed - these are the 4 square devices on the large heatsink to the right of the power transformer. The service manual says these are 2SA1943/2SC5200 (very popular in amplifiers), but your picture suggests they are not. I'd want to see the correct schematic before advising further.
Hi. The 5A fuses are blown and got blown again after I replaced them and the amp is still playing distorted and barely audible ,same from L and R. channel. Also, pictured in the photo is a C300 not a C320 .
The output transistors are P55NE06L. Service manual can be found on ElektroTanya | Service manuals and repair tips for electronics experts.
All, new member here!
I’m hoping this old thread will help me too!
My NAD C300 is also misbehaving!
I’ve got this weird thing where intermittently the sound will almost disappear from one channel or it will start to vibrate as if the speaker cone is damaged.
I’ve substitute different speakers, wiring, music source and input channels so I know the problem’s with the amp.
I’ve put a multimeter on the speaker outputs. One side looks normal (I’m no expert at all!) but the other side dips into a minus reading.
No fuses are blown and sometimes it all works fine! Can’t get to the bottom of it!
Any thoughts would be great!
I’m hoping this old thread will help me too!
My NAD C300 is also misbehaving!
I’ve got this weird thing where intermittently the sound will almost disappear from one channel or it will start to vibrate as if the speaker cone is damaged.
I’ve substitute different speakers, wiring, music source and input channels so I know the problem’s with the amp.
I’ve put a multimeter on the speaker outputs. One side looks normal (I’m no expert at all!) but the other side dips into a minus reading.
No fuses are blown and sometimes it all works fine! Can’t get to the bottom of it!
Any thoughts would be great!
The fact it sometimes works OK means you might get lucky and find it is a badly soldered joint but you would have to give the board a very thorough examination to check. It can be hard to spot.
Other potential problems could be an intermittent transistor junction, typically on devices that run hot. Such issues show on careful voltage checks around the devices but you would need at least a basic understanding of semiconductor theory to determine incorrect values. Typically a B-E junction will suddenly go partially open circuit and see a large increase in voltage across it.
I would recommend NOT to have speakers connected while testing and waiting for the fault to appear as the problem sounds like it could damage a speaker and also cause the amp to catastrophically fail.
Other potential problems could be an intermittent transistor junction, typically on devices that run hot. Such issues show on careful voltage checks around the devices but you would need at least a basic understanding of semiconductor theory to determine incorrect values. Typically a B-E junction will suddenly go partially open circuit and see a large increase in voltage across it.
I would recommend NOT to have speakers connected while testing and waiting for the fault to appear as the problem sounds like it could damage a speaker and also cause the amp to catastrophically fail.
Many thanks, Mooly.
Since your answer I have decided to do a couple more things - mainly because I have no clue as to how to fix the thing! And I don't have a basic understanding of semicnductor theory!
All the issues occur when I am listening to Spotify. The amp is a hand-me-down from my parents, who I am pretty sure used it with no problems. Since I have used it with Spotify I have had the above problem.
The spotify gets to the amp from either an iPad or laptop from the jack output (usually) thru a Quad preamp then into the NAD via one of the phono inputs on the backside.
I am now listening to the second of two CDs and it has been faultless!
Could this be something to do with the type of signal/input/input voltage that an iPad or computer puts out ?
Many thanks again, all!
Since your answer I have decided to do a couple more things - mainly because I have no clue as to how to fix the thing! And I don't have a basic understanding of semicnductor theory!
All the issues occur when I am listening to Spotify. The amp is a hand-me-down from my parents, who I am pretty sure used it with no problems. Since I have used it with Spotify I have had the above problem.
The spotify gets to the amp from either an iPad or laptop from the jack output (usually) thru a Quad preamp then into the NAD via one of the phono inputs on the backside.
I am now listening to the second of two CDs and it has been faultless!
Could this be something to do with the type of signal/input/input voltage that an iPad or computer puts out ?
Many thanks again, all!
You say you connected the output of an ipad/PC via the amplifier's phono input? I think that's likely the the problem.
The phono source level is very small (only a few mV sensitivity) and the output of your laptop, iPad, preamp etc can be much higher, overloading the amplifier's own preamp and causing gross distortion. Feed the signal in via a line level input such as the CD input or "tape in" input etc, then select that source and recheck the sound. You now may have to increase the volume level to match what you are accustomed to, though.
BTW, the C300 is an integrated amp and doesn't need another preamp between the source and amplifier. If your lead from the laptop etc. has RCA plugs, it should fit any of the C300 (don't use phono) inputs directly.
The phono source level is very small (only a few mV sensitivity) and the output of your laptop, iPad, preamp etc can be much higher, overloading the amplifier's own preamp and causing gross distortion. Feed the signal in via a line level input such as the CD input or "tape in" input etc, then select that source and recheck the sound. You now may have to increase the volume level to match what you are accustomed to, though.
BTW, the C300 is an integrated amp and doesn't need another preamp between the source and amplifier. If your lead from the laptop etc. has RCA plugs, it should fit any of the C300 (don't use phono) inputs directly.
Last edited:
As Ian says, a phono input (for a turntable) is totally unsuitable.
If you just meant one of the normal line inputs such as CD or tuner etc then those are OK.
You mentioned in your first post that it is one channel affected.
Have you tried swapping the leads to the Quad pre-amp input over to see if the problem swaps channels or not.
If it doesn't and the fault remains on the same channel then try swapping the Quad outputs to the NAD over.
If you just meant one of the normal line inputs such as CD or tuner etc then those are OK.
You mentioned in your first post that it is one channel affected.
Have you tried swapping the leads to the Quad pre-amp input over to see if the problem swaps channels or not.
If it doesn't and the fault remains on the same channel then try swapping the Quad outputs to the NAD over.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.