NAD C350 - Repairs Part 2 (Ep. 102)
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- Опубліковано 2 гру 2021
- This one was a head scratcher and I'm still not sure how many faults I repaired but it's working now
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I am a hobbiest and amplifire collecter . You are a very good teacher. Explanation and practical aspect are perfect. I learn lot from these two videos, thanks lot.
I'm glad you found them useful, cheers
Thank you posting these videos! Give a chance to learn fault finding. Great to see the different problems and the way to find the solutions, shortening the repair time for the others. I am currently repairing a 1990 Yamaha ax-440 and it is miracle how well holding its caps comparing to the NADs.
I'm in the middle of repairing this very same amp, and watching you work on this one was a real education. I've been pausing your video and scribbling notes in the service manual. Thank you! Bought my C350 new in the early aughts. It is not as roasted inside as the two you worked on, but still had plenty of bad caps and other signs of heavy wear from the heat. Mine was out in the open without anything sitting on it for its entire service life. I guess these run hot!
Thank you for your time posting these videos. Excellent work. Thank you!
You're welcome, thanks!
I like how you also address potential problems that are likely to occur in the near future. Like dry thermal pads. Without thermal paste probably more than 50% of the surface area is not transferring heat through conduction and convection transfer just doesn't cut it.
Trevor, I have the C340 model. I bought it new in 1999 and still use it every day. I took it in for service in 2010 for a failed channel and in 2019 for the defective tone defeat switch. The service was performed by NAD technicians and it was very cheap to service the amp. NAD is definitely the best value all around. I can't imagine buying anything else.
Good to hear your NAD is keeping you happy. Looks like you got one that wasn't made on a Monday or Friday!
@@TrevorsBench I really think people do not take care of their amplifiers. Proper ventilation is the key. I was perplexed by the amount of bad components in those two NAD C350s. Something was very wrong there. Maybe owner had components stacked one on top of the other. It's a recipe for disaster.
@@Coilaman Maybe you're right. My perception of NAD is biased from my experiences. I'm sure there is NAD gear out there working great after 20 years
I had similar issues with C352, for failed channel, i reflowed pre amp section transistor and i removed tone defeat switch altogether . So it's now on permanent tone defeat. Installed cooling fan
Great job 😃😃👍👍
This started off as some kind of head scratcher. A little poor QC during the manufacturing phase of the little transistor heat sinks coupled with what must have been years long blast furnace level heat environment. Great work! Another quality piece ready for its next life! Thanks for your time posting these.
Thanks for your comments and views Craig. Glad to see these go back to the owner sounding good again.
It was good to see the ol' Diet Pepsi can on the bench again. I don't recall seeing one in the part 1 video.
Lol, I'm trying to cut back on that stuff
@@TrevorsBench Good luck. I'm in the same boat with Diet Coke. I need the caffeine and I hate tea and coffee really messes with my heart.
Great videos Trevor, really enjoyed watching you work. I've owned a C-352 since new. In May I gave it a service and pulled some caps for testing, everything was within spec', admittedly the C-352 is a newer model than the 2 you repaired (same caps etc through). As you mentioned in part one these 2 amps are really victims of heavy use in a cabinet with insufficient ventilation. Studios cheaping out with consumer grade amps in racks never ends well. I've had a few NAD amps and also like how they sound. If an old NAD 2200 power amp crosses your bench for a re-cap or relay repair, don't let it leave!
I have a NAD C326BEE upcoming soon but i expect it will be loaded with all the classic NAD failures such as cracked solders and dead caps.
I'm not a big NAD fanboy. While they are great sounding pieces, I feel they could have put more effort into fit & finish. The grey/black plastic fronts & knobs turn me off of the brand
@@TrevorsBench Looking forward to the video Trevor. NAD have always been about good sound quality at a budget price. Their older amps were generally better constructed. Tnx for the videos.
I was thinking about one of these used as a backup, the heat sinking is an epic fail, no wonder there's talk of reliability issues on the forums. The power transistors sinking simply boggles the mind, if this was a car it would be called a lemon. As for the careless sinking and dried grease on the others I've opened up 50y/o Japanese audio gear where the compound was still soft and fine, so it's just a matter of caring enough to source good product. No NADs of any type for me.
nice one!...reminds me of my old days working on thyristor DC motor drives, working the circuit backwards, lifting component legs until the culprit was found
Yeah. sometimes when there's a lot going on the best way is divide & conquer. Thanks for watching. Cheers
Excellent and very informative. Thank you.
Thank you for watching
Excellent... learnt a lot..
Thanks for the video, very useful
Watching you service these amplifiers, I would love to see someone reviewing the latest generation of brand new amplifiers, from a point of view of build quality, serviceability etc. I am about to purchase a new amp to replace an old, perfectly working Technics amplifier - it is not cost effective to have it serviced. I can see the recommendations from various reviewers, but they all talk about performance etc, they do not major on build quality et al. which means I am completely in the dark when making a purchase.
I would love to do testing & reviews but first I would need to convince the manufacturer to send me the gear. Build quality is a big thing for me too. It's something manufacturers don't talk about much because consumers usually focus on specs and price
It went out because there’s a protection built in when there no speakers connected
No harm in running modern transistor amplifiers without a load as long as the frequency remains low. In fact, most amps allow you to switch off the speakers so you can use headphones which are high impedance. The protection shutdown the amp because there was 10v on the speaker outputs. Cheers
29:00 Time to break out the FLIR camera.
Great video. This is one of (if not the most) complicated repair videos I've seen on UA-cam. I am a little aprehensive now to tackle my 2 NAD amplifiers I have to repair :) How did you check that transistor for leakage, just ohmmeter in circuit?
I see your using the wife’s toothbrush for cleaning boards I do the same. Nice fault finding
Yes, I find it makes my toothbrush taste funny. Now that I switched I no longer have that problem
Cheers
Interesting. I bought NAD c355 a week ago. Was wondering why it is hot all the time.
ive always found it easier to use a Dearson Val meter for dc offset
Analog meter movements are easier to view and use but are not as sensitive. Digital meters have some lag and can be difficult to read but have higher sensitivity.
For zero balance we don't need ultimate accuracy or sensitivity but getting it close is good enough.
Generally, anything less than 50mV isn't worth stressing over. Also, it will drift as the amplifier warms up with use so trying to get absolute 0v is pointless
Electrolytic caps where would we be without them? yet another great fault finding presentation Trevor, head scratcher? I actually got down to saw dust but managed to get a plaster on before I lost it all :-) Is that analogue a Micronta it looks identical to mine, I got it sooooo many years ago and it's still working really well, much better than me!
Hi, Trevor, thank you very much for the wonderful video on repairing the nad amplifier.The washers shown on the power stage transistors look like they are mineral mica. Mineral mica is an extremely good conductor of heat.
For this reason, I never use thermal paste when installing and using mica insulators between power semiconductors and heatsinks.
Or am I wrong?
Many greetings from Soest Germany.
Good day friend, I suggest using a thermal paste/grease/putty/bonding adhesive with mineral mica washers. There are microscopic imperfections on the mating surfaces of the heat sink, washer and semiconductor. Without a thermal paste, there can be trapped air pockets that will insulate the washer from metal reducing heat transfer somewhat
Great video, Why not add a fan to the amp.
People dislike fans in audio gear
Hi Trevor, any change you doing a Vid on THD measurement?!
If I knew what I was doing, I could make such videos, lol, seriously I would need to upgrade some test gear around here first
Good idea, I'll keep this in mind for a future video
These amps are begging to have fans installed. Never seen anything that ''new'' with so many caps outright failed.
Having found that the thermal compound was dry on this amp, did you go back and address that issue on the other amp? Also addressing the problem with the heatsink mounting.
I must say, I am disappointed with the build quality of these NAD Amplifiers. To have piggy backed two transistors on a single heatsink smacks of poor design, and to have left ridges on the mounting holes so the transistors do not lie flat to the heatsink is doubly poor. It is no wonder some NAD amps have a reputation for running hot.
It may be intentional- it allows for close thermal tracking and minimizes gain disparity due to differences in temperature between (ideally) matched ICs. You will see it implemented more often with differential input pairs. It could have been handled better, no doubt.
I have seen AV racks in air conditioned rooms, room temperature rooms and stuck into coat closets with the door shut. Somewhat hilarious and sad at the same time.