Enermax Tomahawk ETK450AWT PSU Repair

[eigma]

A few weeks ago my computer power supply (Enermax Tomahawk ETK450AWT) stopped working. Of course this led me down a reverse engineering and circuit debugging rabbit hole ;-) I also learned about capacitor Equivalent series resistance along the way, and wrote an article about it all. Here are some sneak peeks:







And the full article:
https://github.com/cpatulea/src/blob...awt-psu-repair

Enjoy!

[sam_sam_sam]

Re: Enermax Tomahawk ETK450AWT PSU Repair

Very interesting article

But I have a question for you about the aux winding where you put the extra capacitors in parallel

How does the switching power supply work on a load on all of the power rails and what voltages did you get
And what was the results on the scope display if you had showed these results it would have been a better article for learning purposes

I have only skimmed the article so far but plain to read more carefully later

[momaka]

Re: Enermax Tomahawk ETK450AWT PSU Repair

Very nice write up, eigma.
I really enjoyed reading through your troubleshooting steps and how you got to finding those bad caps.

Those small caps going bad are quite a common occurrence we've seen around here - especially Teapo brand. In the case of your PSU, we typically call these the "startup" caps in the PSU, since they are responsible for filtering the primary-side auxiliary rail... which provides start-up and running power for both the 5VSB and main PS control circuits. Whenever I see a PSU that is misbehaving and it has capacitors from 2nd tier or worse brand (i.e. known crap cap brand), I always start pulling caps and checking things on my ESR meter. More often than not, those crap cap brands will be bad, especially after many years of use. And in regard to those small caps, they don't even bulge or look bad most of the time, which is why people sometimes tend to overlook them. For this reason, I personally keep a small stash of common values that I see used as "startup" caps in PSUs (typically 10 uF, 22 uF, 47 uF, and 100 uF @ 25-50V... so I stock these mostly in 50V variety.)

Aside from the startup cap, I see your PSU is full of other Teapo and Samxon capacitors (the Teapo look like SC series, which do often start to fail after 8-10 years, or sometimes even less.) Probably best to replace ALL of the capacitors on the output of the PSU if you plan on using it for many more years. Also, your primary input filter cap is a Samxon that is only rated for 400V. Since this PSU has Active PFC, my suggestion is to replace this cap as well. Just make sure to go with a reputable Japanese cap brand and pick a cap rated for 105C. It's also a good idea to go with a 420V or 450V -rated cap. This last part is actually important. Since many APFC circuits run their boosted voltages up to 380-390V, a regular 400V-rated cap take a lot of beating from the APFC. In my experience, 420V and 450V caps tend to last longer. Couple that with a high-quality Japanese brand (Rubycon, Panasonic, Nichicon, or United Chemicon), and you should not have issues with the cap failing there for a very long time. Otherwise, with cheap cap brands, it's a bit of a Russian roulette when that cap will fail. I've seen more than a few now to convince me that wimpy caps should never be used on the APFC. When they fail, they typically take out the APFC MOSFETs and sometimes other primary-side components too. At that point, the repair becomes complicated and uneconomical at the very least.

Anyways, thanks again for sharing your repair with us and hope to see you around here more often!

[sam_sam_sam]

Re: Enermax Tomahawk ETK450AWT PSU Repair

After reading in more detail
I find that for the most part it is well written ( thank you for writing this troubleshooting guide )
I did find where you explain part of this about the statement that I made earlier

“ And what was the results on the scope display ”
Where you explain it is where you have the write up about checking capacitor ESR with a scope

Unfortunately I do not have a scope but I do have a capacitor ESR tester which I use all the time

[eigma]

Re: Enermax Tomahawk ETK450AWT PSU Repair

Thanks everyone for the kind words. (I neglected to enable e-mail notifications and only just noticed the replies)

Thanks also for the tips about capacitor quality. For a while I figured "replace all the caps" was some misguided effort rooted in myth - but having spotted such a failure myself first hand, I'm starting to understand the wisdom.

I'm not sure if I'll use the PSU (I've already ordered and installed a replacement) but all good to know anyway.

sam_sam_sam, glad you found the info.

[momaka]

Re: Enermax Tomahawk ETK450AWT PSU Repair

For a while I figured "replace all the caps" was some misguided effort rooted in myth - but having spotted such a failure myself first hand, I'm starting to understand the wisdom.

Well, it can still be a myth in some cases, as some people will blindly suggest to do a recap without trying at all to figure out what the issue is first.

But in reallity, it really depends on the capacitor brands used in the device, which is what this forum was founded on pretty much.

The good Japanese brands (Rubycon, Panasonic/Matsushita, Nichicon, United Chemicon / Nippon Chemicon, and Sanyo / Suncon ) are generally very reliable and rarely need the "replace all" treatment. The very few instances where this might apply is in very old and very used equipment - we are talking about devices that have been in service for over 15-20 years and have seen a lot of harsh temperature environments. Outside of that, these good Japanese caps tends to last for many decades, for the most part (there are, of course, certain series from these brands that are an exception and have been known to fail a lot... but again, for the most part, these brands are reliable.)

On the other hand, most Taiwanese, Korean, and Chinese brands haven't had anywhere this good of a track record when it comes to reliability (some even downright terrible, especially the very obscure Chinese brands no one has ever heard of.) So when dealing with anything outside of the Japanese brands mentioned above, the general advice is to pull caps and test out of circuit.

There are now cheap multi-function component testers (like GM328 and similar) that can do capacitance and ESR measurement on capacitors... and they are decently accurate - which is quite handy for those of us who don't have an o-scope or more expensive LCR meters.

Chances are, if you work on a lot of PSU and audio equipment (especially non-commercial units), you will find the component tester mentioned above a very valuable tool, as it will be able to find bad caps very quickly.

I'm not sure if I'll use the PSU (I've already ordered and installed a replacement) but all good to know anyway.

It's a pretty decent PSU. With a full recap, it should provide at least 2 decades of useful life. Of course, it all comes down to having the time to do it. Some people don't, and that's understandable.