NAD OWNERS THREAD

[reubensm]

Hello fellow NAD owners. I have owed and enjoyed NAD products over 25 years. It begun with my dad and I am continuing this, after his recent passing.

One particular product is the flagship 208 THX amp. It has been well-cared for a lover the years by my dad who got it brand new to power his Focal speakers. The Harman Kardons were just doing those Focals any justice and he got these monsters to make sure power was never a limiting factor in the setup. Recently the amp developed a strange issue during power ups. The NAD techs have been left puzzled by this as there can't seem to point to the problem.

I thought this issue might be something suited for the technically inclined members here who may or may not have encountered such a problem and found a solution had there been one.

The setup and operation sequence:

I have a streamer that serves as a preamp(Primare i15) that is connected to the power amp(NAD 208) using an RCA connection. There is no 12v trigger running from the Pre to the Power. Therefore, when I switch on the system, it will be the Pre powered first followed by the Power. The LED goes from RED to GREEN after the relay clicks, within a second or two. However, this has not been the case with my unit.

The initial fault:

Earlier this year, when this sequence was followed- Power amp after the Pre amp, the standby red LED came on but the relay took anywhere between a few seconds to 8 mins(yes! 8 mins on some days). I thought this was normal because once the relay clicked, showing the green LED, it was ready to go. The amp played for hours without any problems.

One fine day, following the same power up sequence, the relay took a minute to click and when it did, the red led did not switch to green. There was in fact a double click as though a rocker switch was switched on and off. A loud thud sound was emitted from the speakers. It was really loud as though the woofers had blown. I immediately switched off the Power amp and the mains.

When this was brought to NAD they could not replicate this problem with their setup. The only thing that they could observe was the delay in the relay(approx 1 minute) but this was not consistent. At times, it would just power on as normal with the relays clicking instantaneously. Whereas, at other times, it took a few seconds. One thing I observed at home was that if it was used everyday for an hour or so, it would switch on without any delay the next day. A few days of no usage would see the amp acting up. But we were unable to establish this firmly because back in the workshop, it powered on within seconds despite being left tuned off for a few days. So far, only the 220uf cap in the protection circuit has been replaced.it worked fine for week and the delay slowly creeped up. someone who is familiar resolving such a problem can point me in the right direction because, all we are doing now is guesswork, with hope that the problem is resolved.

Thank you for taking time to read my post. Appreciate your help, lads.

A very nice description clearly explaining the issue and the symptoms. Trouble with standby mode, delays with the protection relays clicking on, intermittent appearances of the issue, etc are all symptoms of failing electrolytic capacitors or failing solder joints. The amp will need a good look up.

 

[JM8488]

A very nice description clearly explaining the issue and the symptoms. Trouble with standby mode, delays with the protection relays clicking on, intermittent appearances of the issue, etc are all symptoms of failing electrolytic capacitors or failing solder joints. The amp will need a good look up.

Thank you for the kind words, reubensm. It was written half-asleep. Apologies for the grammar, misspelled words etc. I felt terrible reading what I wrote- could have checked at least once before posting.

If I may ask, are these caps you are referring to found within the PCB? Some good people with sound knowledge working with electronics identified the problem as being one within the Power Supply board, in particular- the protection circuit.

Earlier today, I made a trip to see the techs and they still could not identify what was really causing this. Atm, we are looking to replace the uP(microprocessor) IC and the relay. The 1uf cap within this circuit is one other component we suspect could have failed and be contributing to this.

Is there anything in particular I must look out for or get the techs to narrow in? The bank of big caps all appear to be in good shape. They measure within specs. The solder joints have been inspected and they look fine as well. Probably I will get them to give it another round of close inspection.

One more thing though. Could it be an issue with the pre-outs of the my preamo that could be causing this? Maybe some Voltage difference etc??

Do let me know. Much appreciated.

 

[reubensm]

Thank you for the kind words, reubensm. It was written half-asleep. Apologies for the grammar, misspelled words etc. I felt terrible reading what I wrote- could have checked at least once before posting.

If I may ask, are these caps you are referring to found within the PCB? Some good people with sound knowledge working with electronics identified the problem as being one within the Power Supply board, in particular- the protection circuit.

Earlier today, I made a trip to see the techs and they still could not identify what was really causing this. Atm, we are looking to replace the uP(microprocessor) IC and the relay. The 1uf cap within this circuit is one other component we suspect could have failed and be contributing to this.

Is there anything in particular I must look out for or get the techs to narrow in? The bank of big caps all appear to be in good shape. They measure within specs. The solder joints have been inspected and they look fine as well. Probably I will get them to give it another round of close inspection.

One more thing though. Could it be an issue with the pre-outs of the my preamo that could be causing this? Maybe some Voltage difference etc??

Do let me know. Much appreciated.

Protection issues in NAD amplifiers are not easy to fix as the root case can be from a large variety of reasons.

The ones with the lower probability are the external factors. The primary external factors are speaker short-circuit or incorrect speaker loads, power (electricity) issues in your area and amplifier overheating or not provided with appropriate ventilation especially when playing at high levels, I am sure you have control over all of these and hence, are not likely to be the reason.

The higher probability ones are the internal ones. The reasons can be many more but the prime suspects can be:

• Failing filter caps
• Incorrect biasing
• Leaky/failing power transistors
• Dry solder joints
• Failing resistors, especially in the bias stages
• Failing relays
• Failing protection circuitry including the protection IC, especially the electrolytic capacitors in the protection stage
• Faulty power supply, especially in the voltage regulation stages
• Faulty thermal sensors
• leakages and short circuits with wiring, contact between the PCB and Cabinet, etc
• Never assume that non-electrolytic capacitors will never give you trouble, these tend to short circuit or drop in capacitance moving towards zero capacitance (sometime even open), when they are failing

Ps: great physical appearance of a capacitor, resistor or semiconductor is not an indicator of proper functionality. These need to be checked electrically to ensure that they are functional per specs.