Modern Tech Fail: NAD C 356BEE Amplifier Repair

[@CuriousMarc]

Holy Molly. Given the comment section, it looks like many vocal people are confused about the basics of voltage, current, power, component ratings and temperature, and are convinced there is another problem in the amp. But this is not the case. The current going in both legs of this auxiliary supply was measured, and it is 237 mA in the +55V leg and 170 mA in the -55V leg. Both normal, with all the components working within their rated power. If you take a second to calculate it, you'd find that the 3.3 Ohm 0.5W resistor, which has a DC current rating of 390 mA (P=I*I*R), was just running at slightly over half its rating. If you take a look at the schematics, you see that the high operating temp is a consequence of this design: the large drop from 55V to 26V has to go to heat, no way around it. That's how linear supplies roll. Fortunately standard resistors are rated to 150C, and power resistors will do up to 270C. So the new larger components are not used in an internet conspiracy to cover up another fault. They are just improving convection cooling and lowering the local PCB temperature. It actually looks like I just applied the same fix that NAD used in its later revisions of the same model.

[@evana3636]

All sounded and looked good to me! Especially mounting those diodes off the PCB. Typical and a shame caps are mounted so close to hot transistors and diodes, etc.

[@hugeshows]

I was thinking there must be another fault because the video glosses over any current calculations you did. I'm glad to see you got to the root of the problem, and sad to see that NAD gave so little regard to where all that heat would wind up. You can't PCB mount components that get their legs hot enough to melt solder, so increasing the surface area of your parts was the only way to go.

[@paulof.8233]

went to check the schematic myself, and it would have been much simpler if they added a couple of outputs in the power transformer with lower voltage instead of lowering the voltage from + and - 55 to + and - 26, the only question I have is how long the amp lasted until it showed the problem.

[@treadmillrepair754]

Hi sir, where I can find a Galvo mirror for 1064nm ? Do you know some seller? Thanks in Advance.

[@Bottleworksnet]

I wonder if they knew who you are and your background, then would they still be making those comments...? I'm loving your videos! Thank you for taking the time to produce them!!

[@pelor92]

I know Audio gear designers are weird, but abusing two poor helpless diodes like that should be a punishable sin XD

[@SteveDaviesCPT]

Yeah - you suspect there is some other fault. But I trust the skills of our fearless leader.

[@pelor92]

​ @mister kluge I suspect I know full well the reason why they did it that way (since I am not the designer of the product I cant know for sure, and I would love to be proven wrong), and it is much, much more mundane than many would think... My guess is that the whole regulation section original design was done for an older/other model, and then carried through to the new one (nothing wrong with that usually) however the main PSU for this specific design runs a higher voltage than the one originally meant for this design. Instead of reworking the design for the section to take the higher voltage, they just bodged in a couple of zeners here and there to drop enough voltage to get into the limits. Again I guess that those supplies are only for the preamp/driver sections, miscelaneous analog and maybe logic, thus not to terribly high current, so this design was deemed acceptable. In the long run however this leads to failure either due to thermal cycling or just overload.

[@CuriousMarc]

@@pelor92 I think you are on to something. They had this custom made, expensive toroidal transformer with the 55V extra secondary from a previous model. Mr. Pinch-Penny working overtime in the procurement department refused to shell out the outrageous NRE for the correct new transformer. I bet you there was an interesting meeting at the company and the engineers were not very pleased with the outcome. So they used what they had and shed the extra 20V in resistors and zeners and PCB cooking heat while cursing accounting. Making this all up, but I sure have lived it in my engineering life. And then made a couple such poor decisions myself later on as a manager. I can't fathom any other reason why you'd use a 55V secondary for a 26V linear supply.

[@PileOfEmptyTapes]

@@CuriousMarc "I can't fathom any other reason why you'd use a 55V secondary for a 26V linear supply." - This kind of thing used to be *very, very* common in integrated amps 30+ years ago. Just cost-cutting, especially when the preamp section is little more than an RIAA preamp. Who'll care about 2 W more power dissipation when the power amp dissipates an order of magnitude more than that? Plus I guess that transformers with extra secondaries are expensive special orders (especially on smaller runs) with little chance of second-sourcing. NAD neither have the kind of production volumes of Yamaha or Pioneer nor are they a premium brand with massive margins, so they really have to watch their BOM cost. It shows. Their stuff is well-engineered but parts quality is really rather _meh_ at times.

[@mywave82]

@@CuriousMarc Maybe a "fix" would be to add one more transformer with a lower secondary voltage inside the case somewhere, and use that instead as supply?

[@goodun2974]

I've repaired many NAD components over the years; virtually all their designs have "hot spots", under-rated components (such as 1/6 watt resistors running too hot to touch, and color codes made illegible by heat), capacitors cooked by radiant heat, broken down solder joints.....and corrosive glue. Even their preamps run hot! (The vertical, chimney-like aluminum-heatsinked voltage-amplifier modules will invariably have bad caps, and they're a royal pain to remove and disassemble for recapping). Many modern NAD amps don't have removable bottoms, and some have only partial bottom panels that don't allow full and complete access to the areas of the circuit board in need of servicing. In retirement, I don't miss working on these!

[@chevon5707]

good 'un Is there any brand of mid-fi amplifier that you *would* recommend?

[@ВладимирПутин-е7м]

@ CuriousMarc - I love the way you run us through the fix and why / what / how you do it. For novices, like myself, this sort of 'narration' is invaluable. Thank you for posting and keep up the great videos.

[@Photoss73]

there are medical doctors, here there are electronic doctors. :-)

[@lawrencebarras1655]

That laser brings back memories. I scavenged a Magnavox Laser Video Disc player, back when I was 18 and they were still in use. I got it working. But I eventually pulled out the HeNe laser tube and the two voice-coil actuated tracking mirrors. Made a laser show out it, feeding left and right audio from music or audio generators. Lots of fun with that HeNe too.

[@tim0steele]

I had a NAD 3030, sold it to a friend so I could get a Technics amp instead. The Technics amp is still working, the NAD amp failed a few months later. I agreed to repair it for him.. cost me a pair of B&W speakers which didn't like DC from the shorted output transistors. The problem was a couple of stages back where the transistors had failed, blowing the subsequent stages. Got it repaired and found the original problem.. he liked listening to records, and NAD were relying on a screw through the PCB to earth it which was slightly loose, causing spikes on the phono input. Adding a ground wire fixed the problem. There was even a tag right there on the chassis but NAD didn't use it.

[@ximalas]

I just learned that "BEE" on the front panel are the initials of Bjørn Erik Edvardsen (Bergen, Norway). Mr. Edvardsen was NAD's second permanent employee. He designed the 3020 back in 1979. He sadly died of cancer in late 2018.

[@sarkybugger5009]

My 3020 is still running sweet. All original parts.

[@dnebdal]

@@sarkybugger5009 I'll admit my computer speakers are driven by a newfangled piece of electronics - a D3020. Apparently they wanted it to fill the same kind of "not very expensive, not ultra-HiFi, but practical and sounds good" niche, and named it in memory of the original 3020. (It is nice, too - convenient set of inputs, will drive a reasonable selection of speakers, sounds good. I have some tiny Dali bookshelf speakers and it's all very pleasant.)

[@Valisk]

My 3020 is still working great too! I bought it second hand in 1996 :)

[@gmcoelho]

That's a very expensive cat toy...

[@SusanAmberBruce]

I like these repair video's, especially when you make a circuit to substitute an unobtainable item or to improve circuit design.

[@Ninjakip]

I’d suggest also replacing the electrolytics near those components. The heat is likely to have cooked the electrolyte. I was working on a similar, slightly older Nad, which uses zeners in the cold start system, and all the electrolytics were out of spec. This is most likely the next failure point of this amp. Thanks for the video!

[@CuriousMarc]

Yes for once I agree with the electrolytic change, the one near the zener is probably a little cooked by now.

[@SeanBZA]

@@CuriousMarc Yes they are JRC, and probably are also Just Really cooked. I typically add a heatsink to high power diodes, using some copper shimstock cut into strips, with a hole drilled into it just to clear the lead diameter, and soldered right by the diode body, so the heat through the leads is conducted away. The major path for heat to escape those diodes is via the legs, not via the plastic body, so the tags on the legs is the best method. Saw this years ago in a Motorola diode application note for the high power Shottky rectifiers, and it really does work well, as they had a nice neat set of graphs showing the effect of various lead lengths, copper plate sizes and versus clamping the diode body in a copper strap attached to a much larger plate. going to make the mounting a little harder, but they do run 40C cooler with only a modest fin each side. As to the NAD branded capacitors, all they are is a generic JRC capacitor that NAD decided to buy a batch with a special sleeve shrunk on, in place of the original, or they just resleeved the cheap ones as a marketing point. Kind of like you can buy various forms of ****fire lithium battery, all with just recycled mystery laptop cells that have been recovered from ewaste, and all with 6-10Ah capacity marked on the 18650 cell, irrespective of what it was.

[@SAerror1]

maybe that's why NAD didn't catch this flaw at the design and manufacturing stage if it takes a while for these amps to fail? cooked electrolyte and possibly general aging causing more leakage and increased power draw through those undersized components?

[@SeanBZA]

@@SAerror1 No, just the thermal cycles will degrade the diodes, and the resistor as well. the degradation is strictly a time and cycle thing, you need to run the resistor hot for a few hundred hours for it to degrade at the full rated power, and the same for the diodes. They just ran the parts at the full rated load, figuring the lifetime would be around 10k hours of operation before failing, and that the fusible resistor would fail first if the diodes went short circuit.

[@FixingOldStuff]

@@CuriousMarc That's what I thought when you installed this little radiator (the heatsink) right next to the (probably already cooked) cap there. Could be a good idea to replace the cap(s) and move it a bit away from the heat source.

[@maximilianbrem8250]

I have a technics amplifier from 1980 and its still running like its new. Amazing build quality back in the days

[@PINKFL0YD-s2h]

First NAD I got was a 3020e it's superb. When they were made in the UK they were very high quality. My 3020e is still working (a friend has it)

[@samvicario]

Thanks for the detailed tutorial CuriousMarc. I had the same problem with my NAD C356BEE. I followed your instructsions and my amp is working again. For some reason my particular unit only had one diode instead of two, so I naturally changed only the one. Again, thank you for your effort and for sharing this video.

[@maryrafuse2297]

I have 2 beautiful Sony amplifiers from the mid 1970's that put this NAD to shame. Both were purchased second hand and both still work flawlessly with sound that is magnificent. The circuit boards look like new, no charred burn marks, and the components and assembly are second to none. The first is the TA-F3A & my second purchase of a Sony amp is a TA-2650. These amps have stood the test of time and best of all they are 1970's SONY.

[@Rob2]

Using a PC slot cover as a generic metal strip... very common :-)

[@wishusknight3009]

I have an NAD 701 receiver which I have owned since new. And it has never failed me. I think this is one that was just on the cusp of them starting to have reliability issues in the mid 90s. I got this one in 1992 or somewhere about. Over the years the amp has undergon some modifications and tweaking to improve its performance. Not so much power output, but overall quality of sound. And its design is very decent, doesn't get too fancy and gets the job done. It doesn't really have too much in the way of shortcomings but is noting particularly special either. They used quality parts and didn't over drive anything like they do now. But the profit margins are tighter now then they used to be for sure. I really have enjoyed it tremendously, and pair it with a decent sub amplifier and woofers.

[@glenslick2774]

The first bit of stereo equipment that I bought new with my hard earned money around 1980 when I was in high school was an NAD 3020 Integrated Amplifier and an NAD 4020A AM/FM Stereo Tuner. Good stuff that never let me down.

[@Allmentux]

Show us your music room :) :D Love the Hifi-projects! Dont hesitate to do more of that ;) Greetings from Germany!

[@jonathanvanier]

Allmentux - Great idea! I second that.

[@nophead]

Seeing how hot the over specked parts get I can't help thinking there is another fault drawing too much current. When PCBs char they turn to carbon and can become conductive. I wonder if that is problem.

[@CherryDT42]

I get that feeling too.

[@Andrew-dp5kf]

I’m sure Louis would have something PP bus related to say on the matter... But yes I agree, he’s looking the symptoms not fixing it fully

[@CuriousMarc]

I checked and the current is perfectly normal (237 mA in the + rail and 170 mA in the - rail). No excessive power consumption. The original parts were running within their rated power. That said they generated too much heat for the PCB which degraded over time. The bigger replacement parts are just easier to cool, not there to patch over anything.

[@dimmog]

I repaired several of these. This is a common issue with 356BEE. Some caps in PSU go bad and start to eat more current because of higher ESR. Zener diodes and resistor start to warm even more and heat up caps more. And eventually it turns out as “snowball” situation. Ideally it needs to be fully recapped because 90% of those caps are bad for sure.

[@ubergeeknz]

Cooking them tends to speed that along... An engineered failure IMHO

[@CuriousMarc]

A high ESR in a cap will cause that cap to heat, not the ballast resistor nor the zener. A shorted component would, but it would be very hot and obvious, and I did not find any. The fusible resistors were working fine when I took them out, they had not triggered. One zener had failed, but the other one apparently took the load and was still working. It’s mostly the PCB that did not like the heat.

[@dimmog]

​@@CuriousMarc Just check ESR and capacitance on caps around heatsinks and zeners they are just 2-15 Ohm resistors now with nanofarad capacitance.

[@ubergeeknz]

I assume the issue is more of leakage (which is another way electrolytic caps degrade) but also some of these consumer gear are engineered within a hairs breadth of the limits in terms of thermal design

[@CuriousMarc]

@dimmog Agreed. I think you have a high chance on being proven right (you mean 10 ohms ESR, not resistors - they’d fail open).

[@Wobblybob2004]

0:18 NAD haven't been British for 30 years, You can blame the Canadians now!

[@CuriousMarc]

Oh really? Thanks, I did not know!

[@rkan2]

The other commonwealth!

[@juslitor]

Hi Marc, how has your amplifier held up ? I had mine since 2015 and never ran into problems with it yet. I wonder if the 230 voltage used on this side of the pond leads to large enough design changes to mitigate the issues you experienced.

[@CuriousMarc]

It’s been problem free since the repair.

[@neilshep50]

I recently repaired an lcd television which had "died" , not even a standby light. Googling the model number found me a circuit diagram and also Fleabay sellers offering a "repair kit" for the common fault. It turned out that in the psu there are three 5amp rated Shottky diodes in parallel. One of these had gone short circuit, the other two were good. So I bought 10 diodes for less than one repair kit. I checked the forward voltage of my new diodes, found a significant spread between them, so selected the best matched triplet for my repair. I believe the fault occurred because one diode took the bulk of the current. I feel that it would have been a better design to have just a single diode with a higher rating.

[@CuriousMarc]

Good electro-sleuthing!

[@DimitriVolkmannSY]

Fun! Before laser were affordable in my teens I used to use old TVs and old stereo amps to drive the vertical and horizontal of the electron beams to make effect boxes we used at parties!

[@rabidpb]

If the 5W parts with heatsinks are running at 60ºC, where the original was 1W rated, there's no way it would have lasted more than a few minutes as designed. I'd be asking what is drawing so much current from that supply circuit, looking for something else that has failed.

[@robertw1871]

Yep, something downstream is surely leaking, I’d be looking at those electrolytics or an IC that’s misbehaving, can’t imagine that circuit should be drawing more than a few milliamps with that amount of drop... agree, even with a hundred times the surface area the temps for that tiny original part are far far beyond anything reasonable and would have less than an hour to live for sure... the temperature of the larger parts will be much lower for a given power that’s exactly why they are physically larger, they radiate over a larger surface area, the thermal conductivity is much higher.

[@CuriousMarc]

The resistors were still alive and well when removed them. Just burned the cheap PCB over time. No other hot component that would indicate a short downstream. Just a ballast doing its thing trying to drop 20V at a couple 100 mA...

[@robertw1871]

CuriousMarc just saying 60c is at the absolute maximum rating for a 5 watt resistor and likely 20 times beyond a 1 watt... if nothing else is wrong then it’s about the worst design in history.... difficult to believe a component would survive long when stressed nearly 20 times its absolute maximum rating... if it’s dropping 20v with nearly an amp through it then a 25 watt would be the minimum power level for a resistor, seems rather insane... maybe incorrect but it just screams to me the current draw should be a couple tens of milliamperes not nearly an amp...

[@CuriousMarc]

@@robertw1871 Resistors running at 60C are not 20 times above their ratings. Most resistors are resistors rated 150C, power ones will do more, up to 270C. Why does 20V equate to 25 Watt?

[@robertw1871]

@@CuriousMarc Ohms law, you stated it has a 20v drop across it and nearly 1 amp of flow, that puts the power dissipation at close to 20 watts, if it's a 1 watt resistor then its 20 times its rated capacity or nearly that...

[@on6rf]

7:35 Using the plier's handle to hold the legs down while soldering is a neat trick! I'll keep that in mind! :) Cheers from Belgium

[@DaCoder]

Are you gonna use that laser setup to listen to / display the oscilloscope music visuals?

[@zyeborm]

I thought that's where this was going. I think perhaps the galvos weren't up to the frequencies

[@juliankandlhofer7553]

a curious marc notification during breakfast is a good way to start the day :)

[@piotrmaj1487]

Thank you for this video. I was wondering why PCB at this place looks overheated in my amp. I will apply your idea to prevent it for burning!

[@TrimeshSZ]

I hope you have that Cesium standard connected to the reference input on the signal generator - you have to make sure the pitch of that A is exact!

[@rogerwalter2500]

I have NAD C352 from 2004 used very sparingly, repairs done over the years- 1 Tone defeat switch failed within 3 yrs. 2 Balance control pot failed after 5 yrs.. 3 Dry solder due to overheating of those same regulators(as seen in video) and slight discoloration underneath PCB due to heat within 5yrs. 4 Front i/p selector switch unresponsive after 3yrs , cleaned it with WD40 5 Installed 12V exhaust fan above pawer amp section on cover and inlet fan (drilling required) over regulator section after end of warranty period. I highly recommend installing fan. 6 Few buttons on remote uresponsive after 3 yrs, now using mobile IR 7 Changed TL082 OPAMP to OPA2134 and installed missing 0.1uF film bypass caps FInally I think DIY amp is best solution, better quality control .

[@gillbates999]

Back in the day (1980s) us starving student audiophiles mostly opted either for the NAD 3020 or the Mission Cyrus 1....glad I went with the Mission. It has been in continuous operation (switched on) since 1985 (though for the last 20 years or so only driving my PC speakers). I only switch it off when I'm gone for more than a few days, which is maybe once a year (ah, the joys of being self-employed...).

[@HenrikG1963]

My NAD C356bee did the same as this one + plus the blue led starting to not working. Pretty pure design and components.

[@joshuawalker7054]

Oh all my oslliscopes are being used.. no matter, I'll just project one on my wall.

[@HappyDiscoDeath]

Frickin laser

[@twilliamson3]

Seems like a missed opportunity for some oscilloscope music....

[@--Zook--]

fyi, like a 2 hour video of just the tones and laser patterns would be a huge hit in the asmr/sleep inducing videos community.

[@alanclarke4646]

You've turned your workshop into a giant one-channel 'scope! 😂😂

[@rich1051414]

I did this years ago with a speaker, a rubber glove, a small mirror, and a laser. It wasn't nearly as neat, but I was able to make 'fuzzy' shapes with certain tones.

[@lokinya]

Listening this video through my NAD C 315. Worked great for over 10 years untill I put it in a 2U rack on my desk and now it starts buzzing if I don't cool it with a fan. Gotta replace the caps soon since they start to go bulgy, so I hope that's the only problem.

[@kaitlyn__L]

it's cool how the mirror contraption ends up making the same shapes as the audio put through an oscilloscope does

[@video99couk]

Check that none of those resistors were supposed to be fusible types. Do I see the marking FS on the schematic? That can mean fusible. Look at the parts list for all resistors you have changed.

[@CuriousMarc]

They were fusible (you can see it clearly written on the schematic). The 3.3 Ohms was replaced with a fusible one, but not the 51 Ohm - I could not find any 5W version :-(. Someone suggested just adding a fuse in series then, which I will do.

[@video99couk]

@@CuriousMarc A 5W fusible would be a hard component to source. Perhaps try NAD or their service agent. In the mean time, perhaps there's been a reason for the cook-up, and it may still be running hotter than it should.

[@CuriousMarc]

@@video99couk Or just put a fuse in series with the resistor.

[@video99couk]

@@CuriousMarc Yes, with a bit of maths to select the right value. Perhaps consider an ICP type fuse (looks like a two legged transistor) for lower current values.

[@CuriousMarc]

@@video99couk Thanks I’ll look that up.

[@Nexfero]

I honestly had no idea what an Optical Galvanometer is before I watched this video; Thanks!

[@ropersonline]

Would the plastic zip ties not get worn out or deformed or damaged by heat over time, making them work less and less well, causing things to get hotter and hotter? Silly question, but are they actually rated for that temperature range?

[@markthackray3185]

Great video. I fixed a terrible sounding NAD C352, those JH caps are complete rubbish. Many were leaking and looking stressed so I just replaced the lot (apart from filters) and is now running sweet. Saying that they are slightly showing signs of bulging on the top. I can't believe those caps shoved right up against those heatsinks are still functional! Not long until they go bye bye.

[@tony359]

"Friday evening" design it seems. "Yeah, a couple of zeners will do, let's get out of here now"... I believe Behringer has something similar in their Truth 2030 and 2031 active speakers. I cannot remember on top of my head but I believe the voltage regulators are dropping 20V too - no heatsinks (why would you need one) and the PCB would eventually fail, leaving the board with either no +15V or without -15V. I had to fix many of those speakers because of that very fault and have installed a heatsink on all the ones I own.

[@tomhoehler3284]

I repaired an inexpensive Crate guitar amplifier years ago, they had a similar setup, one zener in each 45 volt supply rail, with resistors to give a plus and minus 12 volt supply for the preamp IC's. Stupid design, the zeners were running hot as hell, ran away and took out 3 of the IC's. Cheap design. Put in higher wattage zeners and resistors, still working years later.

[@ntsecrets]

My grandfather used to cut non-circular gears using a Fellows gear shaper driven by speaker amplifiers into stepper motors - he used dots on 16mm film to step the motors to get precision cut gears. He later moved it to use paper tape, then my dad converted it to microprocessors and thats how its done to this day.

[@gamerpaddy]

i repaired a few nad's so far. the "newer" series like the nad 310 gets hot enough to melt the isolation washers on the power transistors causing them to short to the heatsink. i stick to the older models from the 80s.. 90s like 3240, 1240, 1155, 2200 and so on. they dont have these problems. still built to a price, but better than most other stuff out there

[@matthewflorianz]

Was considering T778 and wonder if reliability has improved on newer models. Will investigate.

[@projectartichoke]

At least the parts conveniently desolder themselves.

[@NivagSwerdna]

Nice... but did you find the underlying reason it was running so hot? Maybe you have just created a NAD Fire generator Mk2?

[@SorinNicu]

Bad design.

[@NivagSwerdna]

@@SorinNicu OK the design doesn't help but if the amp is sinking a lot of current at idle due to a failure then you will also see this behaviour?

[@bertramlefarge69]

It's great to watch someone who knows what he's doing :)

[@marco56702]

And next projection oscilloscope, just in case you want to project a waveform on the face of a building! Anyway as always world class work!

[@marcuswilson007]

I have repaired audio gear commercially most of my life and been disappointed with the poor quality of manufacturing in NAD equipment that I have worked on, especially considering the supposed reputation of the brand.

[@mankepoot9440]

All my friends who had NAD equipment rave (rightly) about the sound quality. The machines don't last that long though. NAD looks like a holiday love, beautiful but temporarily.

[@chevon5707]

Marcus Wilson any brands you swear by?

[@JoeySchmidt74]

@@chevon5707 Not Marcus, but I'd recommend Cambridge Audio.

[@Lee_Adamson_OCF]

"That's looking a bit tired there..." *yawns and spontaneously combusts. :3*

[@janosnagyj.9540]

13:02 a very high-tech way of cat exercising :)

[@simonkormendy849]

Marc, those displays you were generating are some classic examples of Lissajous displays, you could quite easily adapt it for use as an Oscilloscope.

[@MeriaDuck]

2:55 "tired", that's the euphemism of the day :)

[@SorinNicu]

I want also to add to the suggestion for the electrolytic capacitors replacement! I had refreshed many of my older audio equipment that way. Electrolytic caps from that period, IMO, will last 15-20 years. The bootstrap caps in AB amps will be most sensible to degradation of their value. Those series Zenner diodes (bad design choice) should have been a higher wattage ones (at least 3W ones) and I would install them with longer leads.

[@Kalumbatsch]

Replacing electrolytic capacitors, what a revolutionary idea!

[@cjay2]

Agree. The series zener diodes is a very poor design choice. I always avoided using zeners at all, actually.

[@station240]

Were you not tempted to put a multimeter in series with the zeners/resistors to measure the current ? From the circuit at 6:00 55V in, 24V out, so there is up to 31v across those few parts. I'd suspect there is another fault, either a very leaky capacitor, or the transistors that form the linear regulators are not in linear mode.

[@station240]

@@MartianTech Sure, if you want to do math, and you don't care about the resistance changing due to the resistor running hot. It doesn't work in video though, visually a meter with amps on it is better than a voltage reading and a piece of paper with some calculations. Also you can't measure zeners this way, they don't have a known resistance.

[@Mosfet510]

I like playing with lissajous figures on my scope, but I have never seen one on a wall! Those mirrors were a nice score, good video.

[@kirknelson156]

get a small 12v fan, find a 5v rail and run it off that to keep it quite, should keep enough air moving to keep the components from getting too hot

[@colinstu]

why do those parts get so hot? can the design be improved where massive heatsinking isn't required?

[@CuriousMarc]

It’s a linear supply. That’s how they roll.

[@douro20]

I once worked on a JVC four-channel receiver which had a triple-Darlington class-A output stage for the two front audio channels. Oddly the output transistors had a +200V supply on them.

[@mlbabineaux]

NAD used no-name electrolytics in this amp. I have one, and have repaired it. Put some good Japanese United Chemi-Con 105c , low Z caps in it. C110, 111, 210 and 211 were all OPEN. Change all of those 10uf caps , as well.

[@cfcreative1]

I like the Fluke temp meter.

[@parapotamus]

Most importantly, the heat sinks stop you from seeing the burned PCB areas :)

[@deano023]

I have an old NAD 3155 from the 1980s. I love that old amp, it has such a nice sound.

[@larryl730]

Do you feel amps really have a "sound"? A good amp should only faithfully reproduce the input signal adding nothing but gain?

[@CuriousMarc]

Combo of amps and speakers definitely do, some very markedly so.

[@deano023]

@@CuriousMarc I got it paired up with some Bowers & Wilkins DM309's, so I can completely agree with you there!

[@deano023]

@@larryl730 Absolutely an amp can have a different sound to another one. Its not always about just faithfully reproducing the input they all add their own character to the sound. For example, I find most mainstream amps like Yamaha's and Sony's produce a very bright sound as opposed to NAD's warmer sound. These nuances are even more pronounced with different amplifier technology like valve amps.

[@CuriousMarc]

@Deano023 That was also my first NAD amp. Agree with you, the more refined top end is what drew me to the brand (plus I could afford it!).

[@cryptearth]

as in the behringer video: I'm impressed how supposed-to-be-good/-high-quality stuff seem to crap out on power supply (design) - and about the same issue: undersized (or cheaped out) the components for the load so the overheated

[@giorgiofucci3280]

Hi Marc I am working on the same Amplifier, the traces and solder are very fragile, a good design by NAD but poor execution by subcontractor. Unfortunately I cannot get the -18 VDC rail to work, something is going on with the supply circuit, the LM337 seems to be good (tested independently).......any clues ??

[@tickertape1]

Those are some very crispy diodes

[@SeanBZA]

Operative word is "WERE", they are now very low capacitance glass capacitors, with a breakdown voltage of around 80-200V

[@tickertape1]

Well said never thought of it that way we’ll if I never need an emergency cap I can just look in my hot running amp

[@swebigmac100]

Listening to those chansons on loud volume takes its toll on the amp for sure

[@justjoeblow420]

I know most will probably miss this but this kind of failure is sadly all to common in stereo equipment professional or otherwise. It's actually a bit scary how much studio level gear I've seen the power supply side fail in a similar manner when doing repairs. I did end up with a higher end Yamaha mixing board for live shows thanks to the PSU cooling fan going out and causing a few of the PSU components to fail. I ended up making a small fortune off that thing when I got around to selling it like a month after I fixed it. Got it for doing some minor touch up on a mix for a local band not sure how they ended up with it int he first place as it was massive overkill for most people. I mean how often do you need a full 32 channel mixer than can also do some DMX based light control on certain channels as well.

[@ntsecrets]

You re-created the opening to the Outer Limits

[@d1bergman]

Very NIce, Would you know where I can get a schematic or service manual for a NEC AV-350E? Thanks

[@simmo1024]

I wonder if you could convert an image in to a projected laser via the NAD amplifier?

[@valeriobertucci6159]

in my 355bee, i've always all in protection....3 times in assistance, no way to get it working... i looked in manual, and on the board. The manual talk about resistance r320 and 319, but in the list there aren't notified, and their are missing on the board.....

[@markd9130]

I just sold an NAD 326BEE because some kind of protection circuit kept shutting it down. Local shop could not find a problem. I think it just didn't like the low impedance of my Magnepan speakers. A bit odd because NAD amps and Magnepan speakers should be a good match. Anyways, using an Outlaw Audio Model RR2150 now with no problems...it's a fairly beefy unit for the money.

[@victimovtalent6036]

Still no high power audio amp. using 5Vdc source in high end technology🤔,why they failed to design?

[@kellyherald1390]

So you now have the makings of a laser display oscilloscope. Nice!

[@guycrew728]

Thanks for making videos like these Marc. It makes me more confident that I can repair stuff on my own since I always beat around the bush too much and hardly ever dive straight in. Also don't worry I wont work on power supplies any time soon. ;)

[@kevinwhite9919]

I didn't see in the video - Marc, did you check the 55v input to the zener diodes? if all that stuff is running hot, i wonder if the 55v is out of spec and running up towards 60-80v?

[@CuriousMarc]

Yes I did. Everything appears to be running as designed. Resistors were still working. However one Zener had failed, no doubt from thermal stress. But even that was not enough for the other zener to fail or the fusible resistor to let go. I it just damaged the cheap PCB over time, and the resistors desoldered themselves over thermal cycling. Bad thermal design.

[@MK-rn2hm]

I have been an NAD fan and owner all my audiophile life and never once had a problem with any of its electronics.

[@98karlh]

Something dirty about using zip ties on components that gets hot enough to de-solder (old spec I know).

[@SeanBZA]

Better to use some copper wire, at least then the tinkly bits will not fall off. I just use metal epoxy though, Pratley quickset steel, which is as good as a silpad for mounting those, and transfers heat equally as well, plus actually hold to the metal and plastic.

[@GusFernCa]

I would be concerned about whether zip ties wrapping a component that nominally gets up to 50+°C or higher with the cover closed could easily loosen over time and drop the heat sink that it is holding. This looks like a cascade failure waiting to happen.

[@CuriousMarc]

@@GusFernCa Hehe. If there is a crater in my studio 6 month from now you’ll know why ;-). But I should be OK. 50C is nothing for nylon.

[@electronash]

I recently watched "12voltvids" repair a NAD amp. I believe he titled the video "A Kick in the NADs". lol

[@SkyOctopus1]

Is your "little bracket" made from an ISA slot blanking plate perchance? :)

[@randalltufts3321]

Marc I know you have to love tube amps. How about a little tease? I'm 60 so I still use and build tube amps and repair them. Some of these young people never have seen them. Thanks for the videos

[@FesixGermany]

Galvanometer scanners hooked up to an audio amplifier... memories of 15 years ago came back...

[@evana3636]

Very nice repair, though I think I would have recaped in that area... Too hot for the capacitors, they might be 'ok' now but who knows down the road.

[@CuriousMarc]

Oh you bet. Some caps had been cooked. Not exactly the way I thought, the big ones even near the heat were still decent, but the small 10uF were anywhere from half way down to totally dried up. The closer to the heat the worse it was. Fortunately these are decoupling caps, not filtering ones, so it did not seem to bother the supply nor affect power consumption. All the caps on the main board have been changed while I was at it.

[@yorgle]

Hm... I acquired a couple of galvos with mirrors as well as a red laser module a couple years back. I should probably figure out the pinout on them and try doing something with them...

[@garbleduser]

Did you check the voltage on the power rails? Something could have been over-voltage causing those components to fail early. Also, did you clean off the carbon that had developed between the traces? You may have developed a leakage path at that location.

[@RobSchofield]

I am astonished at the ineptitude of that PSU design... then choosing components with power ratings that are incorrect for the application. Nice video... speechless. My instinctive reaction is that there was a developing fault downstream of the supply causing a higher current draw, but it's difficult to draw a conclusion without looking at what the normal static current draw was in the first place. Sigh. Nice video!

[@robinsonsoto8471]

Hi, Can you tell me how can resistors get shorted instead of open .?????

[@LuxorVan]

Back in the 90's they used to sell a laser light that worked like that and you would hook it up to a stereo and it would cast a light show in a room with different colors. I think spencers used to sell it, they were like $90-$100 maybe more in the early to mid 90's so they weren't cheap but they were fun to play with.

[@letsgocamping88]

But the question is why are the components getting so hot in the first place? Is there something down the line pulling too much current? Or is it bad design and they are dropping too much voltage for their power rating? If so the design engineer didn’t allow any room on his component choice.

[@davidhunt240]

Yeah, there's probably something taking more current than it should, it wouldn't need to take much to burn up this supply...

[@simontay4851]

"bad design and they are dropping too much voltage for their power rating?" Yes, exactly this.

[@pmcgee003]

Imagine being an amplifier in CM's house and thinking you could stop working ... 🤣

[@curtislowe4577]

Long component life, thy name art forced convection. Equipment designed for natural convection is rendered so much happier with small fans to pull air through the cabinet. Filtration is always a good idea.

[@mumiemonstret]

I have the exact same model. Now I have a very strong urge to look inside it...

[@letsgocamping88]

Would be interesting to know if yours runs as hot as Marcs. Could be indication of other fault further down the line.

[@SeanBZA]

@@letsgocamping88 They will all run that hot, unless your mains input voltage is on the bottom end of the input voltage selector range for your local mains. But not much cooler, around 5% lower dissipation from the nominal voltage heat.

[@CuriousMarc]

@mumiemonstret: Let us know what you find!

[@mumiemonstret]

​@@CuriousMarc It doesn't look nearly as charred as yours, but definitely discolored. Funny enough, mine already has a bigger plastic-body diode for D110, and D111 is just a jumper! My R46 is not discolored at all. One difference is that I don't have the DAC module. I can imagine that yours is on for longer periods too, being in a studio. I probably will replace D110, mounting it elevated just like you did, and I also consider replacing R41-R44, R47-R48 with 0.6W versions since they are looking more brown than turquoise.

[@CuriousMarc]

@@mumiemonstret Thanks for taking the time to look and report! I am not surprised that they upgraded the zener...

[@richardkaz2336]

There has to be something else wrong with the power supply for those components to be getting that hot while not really driving the amp hard or into an excessive low inpeadance speaker load.

[@mikaelkarlsson9945]

I agree.. There is no chance that those poor components would have survived 10 years of intense heat. Something else trigger more current to be drawn in the circuit. Upsizing is not a proper way to solve that issue.

[@oudeheer]

Absolutely! This is waiting for another disaster.

[@garci66]

those components were in the input of the low-voltage power supplies (the ones using in the pre-amp and similar). The load on the actual speakers shouldnt matter

[@SeanBZA]

Nope, standard for things in a power supply to run toasty if you have around 200-300mA current draw from the audio processing power supplies, and you are getting that current from the main 55v rails. Quiescent current of a whole lot of JRC dual opamps that are basically a dual 741in a single 8 pin pack, and missing the nulling and strobe pins. Add to that the selection relays, and the headphone amplifier, all running off +-18v rails.

[@lawrencebarras1655]

No, it's a crap design. The LV power supply doesn't care how hard you drive the speakers. Using zener diodes to drop 55v down to something the linear regulators can handle is asking for trouble. The simple volts * current = watts will tell you that. But - it survived the warranty period and some number of years beyond, so technically, it worked and that's good enough for consumer goods. They saved money by not adding a winding, or even a tap to the power transformer.

[@thetaleteller4692]

Built to a price point! Its not so much a profit in components for the company, but if it breaks early you can sell early. The average Customer has no idea how to use an soldering Iron. I have one of those receivers that worked for 30 years on its first set of regulators and capacitors. Electrically it would work another 30 years, but the buttons slowly wear out.

[@johnkristian]

NAD are notorious of placing zener diodes near capacitors. I threw out my NAD and went for Hegel.

[@jogijose4u]

Hi, My NAD C356BEE amplifier makes continues clicking noise and standby light starts blinking on power switch when I try to switch ON'. Also it keeps on standby mode for long time. Before it happens some times but now it comes more often. Some times it gets power ON' and keeps running without no issue till power OFF'. I am looking for a solution to fix this. Please help me to resolve this issue!.

[@CuriousMarc]

Sounds like a problem with your protection module. Unfortunately I have not had this issue so I have never that part of the circuit and cannot help much. Maybe check C121 on the main amp board (mistakenly labeled C12/1 on the schematics).