NAD C272/C372 filter cap failures

[willawake]

Important Advice for C272/C372 Owners

We have seen a small number of filter capacitor failures in and C372/C272 that we would like to bring to your attention. While the actual number of affected units is extremely small (about a dozen units over the last 5 years), the failure is quite spectacular. The problem is that one of the main filter capacitors overheats and blows open. There is a flash and smoke and in some cases the top cover paint melts. This can be alarming as there is an electrical burning smell. In all cases to date, the safety measures built into NAD products have contained the damage to the unit itself.

We have done a lot of research into this problem and have implemented some additional safety measures in order to reduce the number of failures to zero. This failure tends to occur when the mains voltage is high (+10 % of normal mains levels) which is typical in just some parts of the world. However, the main finding of our research is that failure is caused through poor ventilation. It is very important to ensure clear airflow around the unit and that it not be installed in close proximity to a shelf or has anything standing on top that impedes heat dissipation through the vents in the top cover. This includes avoiding having another unit standing on top and if so this must be avoided from now on.

We would like to state that this unit is the top of the range and is a very powerful amplifier. All amplifiers generate heat and the more powerful they are the more heat that needs to be dissipated. We would also suggest that consumers should switch the amplifier off on the front panel when not in use. It allows the unit to totally cool down and additionally it saves on electricity usage.

All units contain installation and operating warnings so we would recommend that consumers read the complete instruction manual from cover to cover.

One additional note: this failure is typically not covered by warranty as these units fail due to incorrect installation and the cost to repair any units that fail will exceed the cost of a new one. However, as a sign of goodwill NAD will replace any customer unit that suffers this failure with a brand new unit, free of charge. Again we cannot stress enough the need for free air flow around the unit.

If you have any questions or concerns regarding this issue, please contact your exclusive NAD distributor in your country.

NAD Electronics

hmm is that really due to heat or crap caps.

we would recommend that consumers read the complete instruction manual from cover to cover.

RTFM n00bs hahahaha

[Hyltz]

My NAD 372 has just blown one of its caps as described above..

The amp is well ventilated but i think it was a power surge that made it commit suicide.

Non the less, please could others share if they have had the same problem and what caps they have chosen to replace the originals. I am currently looking @ Panasonic for the main caps and while I am at it will replace all the caps for the power stage and then move on to replacing "all" the caps on the board at a later date..

Any advise in this regard would be greatly appreciated.

[retiredcaps]

Originally Posted by Hyltz

Any advise in this regard would be greatly appreciated.

I don't know what the original cap value is, but if it is 85C, then try to get at least a 105C and maybe there are some 125C caps?

[Hyltz]

My apologies "retiredcaps"

The NAD 372 main caps are 10000uf, 80v, 105 deg, 35mm dia.

I have found some Panasonic caps to replace ad they are 105 deg's. But was wondering if there where better caps i could use. Say Nichicon?

[japlytic]

Welcome, Hyltz!

On these large NAD-branded capacitors, I see the Chinese "CD" series on them - and I have no reliable way of finding out their ripple current and lifetime.
I still wonder why non-premium components turn up in premium-brand audio equipment...

[kc8adu]

i think that series designation was stolen from cornell-dubiler.
its so common now as to be meaningless.
i would get the lowest esr/highest ripple rating that will fit and even go up a range on voltage.if the empty pads are paralell with one from each group one can up the voltage even at a lower capacitance and add one at the blank.
1 group is for the + supply the other for the -.
will mfrs ever stop putting junk parts in premium gear? probably not since those on forums of this nature are a minority and most sheeple dont do much research into this sort of thing.
would still be interested to know who made the parts and how close they are to the edge.

[ben7]

Interesting pics there!

I bet the main power rails run at like 70-something volts, no wonder why they pop when the mains voltage is high! Also, the CDxxx series thing makes a bell go off in my head - cheapo capacitors... the other capacitors in the amp look very cheap too (lame printing/marking quality, and poor plastic sleeve shrinkage)

[LLLlllou]

Originally Posted by Hyltz

My apologies "retiredcaps"

The NAD 372 main caps are 10000uf, 80v, 105 deg, 35mm dia.

I have found some Panasonic caps to replace ad they are 105 deg's. But was wondering if there where better caps i could use. Say Nichicon?

Panasonic is as good, if not better than, Nichicon, depends on the series, but Panny is one of the only manufacturers that has NEVER had a bad series.

The extra unpopulated spots on the board allow you some upgradabillity.

Removing all 4 10,000uF 80V caps, and replacing them with 6 8200uF 100V caps, means you never have to worry about overvolting them again, plus you get a little increase in capacitance.

Digikey has these:
http://www.digikey.com/product-detai...0651-ND/272791
Panasonic T-HA series, 105 deg., massive 5A ripple rating, 35MM diam. Problem is these are 4 terminal, so check the data sheet to see if they will fit, looks like the board has extra holes for 4 pin caps, but they may not line up correctly. They' also 80MM high, you didn't mention how high the originals are.

[Hyltz]

Hi Guys.

Many thanks for the feedback and suggestions.

LLLlllou : the current caps are 4 pin, so they should be perfect, thanks very much for the link. I will have a word with my "electronic guru" this side and see what he thinks.

Will post some pics of the upgrade and let you guys know what we decide to go with.

[LAB3]

Old thread and my first post here so hi to all. .... I just purchased (waiting on USPS) a NAD C272 amp serial# H4XC27204475. How can I find out what year this one is????????? I read this thread about the "cap mod" I am invested in this now :-) any help would be appreciated. I have had fans on all my equipment (Ham and stereo/ HT gear)for years and never stack. I will NOT be bi amping, doubt I will need more then 70 watts per channel(Klipsch Cornwals) efficient speakers in small den.. I am mating the C272 with my C162 for my TT and R2R.. Googled C272 and found this thread any links to other NAD needed.

Thanks
Louis

[common-sense]

Yeah, I know ... zombie thread.

I restore vintage amps and receivers and I just finished another not-so-vintage C372. Here are my findings regarding capacitor/reliability issues with these units.

* the PCB layout fosters caps prematurely failing. If you notice the red arrows to the right of the transformer...that's the PS regulation stage. If you look closely, you can see where I'd added an aluminum heat sink on top of the factory heat sink (courtesy of JB Weld and yes, JB Weld transfers heat). Those heat sinks get glaringly hot! ...and there are caps right next to them. If caps fail, it can cascade to active parts (like transistors) and you wind up with a mess.

The regulation stage is also below the right channel amplifier board and since heat rises, this are other considerations when rebuilding these units. On the back side of a couple of the red-arrowed heat sinks, there are some electrolytic caps. I've chosen to mount them at a 90 degree angle to the board so they're away from the heat.

And one more heat-generating area are those four wirewound resistors at the top of the amplifier boards. Those get silly hot as well! The factory calls for 3W rated resistors in those holes, but for more heat dissipation, I'd replaced them with a 5W rating.

* the factory caps do not appear to be what one might consider, top drawer name brand, though they are NAD branded. This is usually an accounting decision and if you want to bring a piece of gear to market at a competitive price point, concessions may have to be made in manufacturing. Rail voltages to the amp boards on the C372 are +/-68VDC. Even with a 10% variance over spec, the factory 80V rated main filter caps are still within operating parameters. NAD had a TSB (technical service bulletin) specifying adding wire in parallel with the PCB traces for the main filter caps to mitigate resistance-related heat failure issues for those caps. I'm of the opinion that the failure mode for the main filter caps wasn't PCB trace resistance and attendant heat, rather the deficient amount of electrolyte in the caps dried out and POOF!

Regarding cap failure close to the regulation stage -- which is actually more prevalent -- it's obvious the cap failures there are heat related.

What would I have done differently to address heat/capacitor related issues?

For starters, I would've mounted the toroidal transformer upright, which would allow for more available PCB real estate to spread out heat generating components. I would've mounted the amp board heat sinks externally for better convection, not under the cover and I would've spent another $50 (or less) on quality caps, then raised the retail price $100. Win-win.

The design of NAD gear is well thought out, but implementation of it is lacking with this vintage. fwiw...