A couple of years ago I decided to build myself some class-d amps based on the Hypex NC400 modules. I had also designed some custom billet aluminum cases but I knew they were going to take a while so I put them in temporary enclosures. I had noticed during the summer months when the weather was warmer, one channel would click off. I finally figured out it was thermal shutdown and so I turned the case over and put some metal objects on top to act as heat sinks.
Fast forward to a couple weeks ago, I needed to turn my equipment off to make some changes to the setup. It took me overnight to make all of the changes and when I went to plug the amps in the next day, neither would turn on. No signs of life at all. No clicks, no lights, nothing. I was a little confused that both could die at the same time. They are in separate cases on opposite sides of the room but when I popped them open, I reached for my cap wizard and started testing out some of the caps in the power supply. Turned out several were cooked. Some did not even move the needle on the cap wizard. To my suprise, even one of the largest caps, a 820uf @ 200v, had drifted far out of spec.
I decided I would just replace all of the caps on the power supply boards because I wanted to make sure they were perfectly matched and I figured they all probably have a shortened life span from the heat they incurred. My first task was to remove and map out all of the caps. To get to the 2 largest caps on the board, the large heatsink HS1 needed to be removed. In order to remove that large heat sink, R2 needed to first be removed to access the screw holding D43 to the heat sink. After I got that out of the way, then I could remove and catalog the caps. This board is not particularly easy to work with. The holes are drilled with very small tolerances compared to most. This means you really need to get all of the solder out of the holes or the new components won’t go in easily.
4x 820uf 200v (C1, C15) http://www.digikey.com/product-detail/en/LGW2D821MELB30/493-8519-ND/1966875
16x 220uf 35v (C3, C4, C5, C6, C7, C8, C13, C14) http://www.digikey.com/product-search/en?vendor=0&keywords=35ZLS220MEFC8X11.5
4x 22uf 63v (C22,C26) http://www.digikey.com/product-search/en?KeyWords=63YXJ22M5X11&WT.z_header=search_go
2x 470uf 50v (C9) http://www.digikey.com/product-detail/en/UHW1H471MPD/493-6972-ND/3664388
12x 100uf 100v (C10, C11, C12, C19, C20, C21) http://www.digikey.com/product-detail/en/100YXJ100M10X20/1189-2149-ND/3563802
After that, I ordered the caps for about $40 shipped and replaced them when they showed up. So far so good. Everything seems to be working again. Lesson learned. Even though these amps use a very small amount of power and run very cool for their power outputs, cooling is still super important. I would suggest having plenty of cross-ventilation in your cases. Make sure you leave adequate distance between the amp and power supply. Also make sure your NC400 module is attached to a larger and thicker piece of metal to properly cool it. Apparently a smallish piece of light gauge aluminum is not adequate when in an enclosed space. If you need to replace your caps, ONLY use 105 degree varieties and use the ones rated for the most amount of hours at that temperature.
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Thank you for this article. I built a pair of SMPS600+NC400 just over eight years ago, approx. 2012. One of the SMPS600s is mounted vertically (long side top) and the other horizontally. The horizontally mounted one started becoming slow to click-on, then intermittently wouldn’t click-on, then failed altogether. I could see that the two big capacitors, C1 & C15 (820uF 200V) had deformed a bit, with bulging tops. I bought four of these capacitors, replaced both on the failed SMPS600 and will keep the other two in case the other SMPS600 fails. The failed SMPS600 now works fine – correct operation of both NC400 units restored.
An update on my comment above. Within a few days of repair, the suspect power supply became intermittently slow to click-on then failed again as before. This time, I replaced all the can-type electrolytic capacitors on the live side of the board. It’s now been a few days, and the suspect supply has always clicked-on within 0.5 secs of the good one. I’m about 90% confident it’s fixed, but will comment again if not. Also, I’ve now mounted the suspect supply vertically, long side up, like the good one in order to promote better air flow across the heatsink on the live side. Again, thank you for this article.
Hi Mark – very interesting to read your comments here, I have almost exactly the same situation. I built a pair of monoblock NC400 + SMPS600 in around 2013. They haven’t been much used and have been in storage recently. i got them out and after a while, one amp failed. It seems to be the SMPS600, no output! The relay is not clicking, but no caps are bulging…
I will have to try measuring the 820uF caps to see if they are failing. Jos at Hypex has given me some tips, he seems to think the 220uF caps are worth checking. I’ll check back here and see what else I can find out…
I JUST had it happen again a couple weeks ago and went through the process of recapping a power supply module. I ordered enough caps to do two modules and I think it was $45 shipped. The ones that actually tested bad were the smallest ones near the two huge caps. All of the rest that I tested still checked out but I went ahead and replaced them all since it wasn’t much more effort to do so. Slapped it back together and it’s working perfectly again.
Hi Geordy, very interesting. Those small caps were the ones that have been suggested to me. I am waiting the delivery of a cheap LCR meter to check things out a bit – I think I threw my old one away a few weeks ago, grr…
One thing – the relays on mine are not clicking, a few seconds after power on. Did that happen on yours? I was told that the relays are for bypassing the inlet rush current limiter, and for 115V use (I am on 230V)
On mine, the amp would click the relay on and then immediately click off and shut down. After a few seconds the cycle would repeat. When it turned off, all the lights turned off and it looked totally dead. Then it would spring back to life from the dead.
Geordy, I stumbled over this site googling the same problem with my SMPS-600 modules. I left them on for years. After being up for probably 2 years continuously, I powered them off to do some electrical work on the house and upon restart, they both just click and shut off, then repeatedly try every several seconds. I tested caps for shorts and compared the cap bank capacitance and there is nothing obviously wrong. With your caps, did they test as shorts or have low resistance?
C14 failed on both my units, which had been operating continuously for more than a year. I recapped the input side of each and both are now working again. I think leaving these on all the time just eats up the cap lifespan.
Curious what kind of case you are running it in? I still wonder if it’s the heat or if these power supplies are just exceptionally hard on a couple of the caps.
Mine were low ESR, never shorted.
Wow, just had the exact same thing. My pair has been on for over a year and I switched them off for a day. I switched them on the next day and one would not turn back on, no click or anything, I opened it up and tried the power supply from the working one and that worked. I can’t see any bulges though.
G
I have had to do this repair probably 3x on each of my 4 channels now and I’ve never seen my caps bulging even a single time. I highly suggest getting yourself a cap wizard and taking the guesswork out of repairs like this. It’s dead simple to use, typically if it beeps, it’s good, if it reads low, it’s probably bad. If you have any doubts, check it against a brand new/known good cap. https://www.howardelectronics.com/specialty/capacitor-wizard-esr-meter/capwiz-midwest-devices-capacitor-wizard-esr-tester-cap1b/