A Tale of Two Power Supplies

Haze the New Guy

The next stop is the Autiotek AT-PS4. Our first impressions are good, other than the initial odor of cheap petrochemicals. There is a three-wire power cord, suggesting a ground. There is a fuse holder, suggesting fusing. Since résumé padding is a real thing, we will need to get inside to validate these claims. That task again presents us with six screws, in one way better than the old unit, and in another way worse.

New supply opened

As clean inside as it was outside.

Already this is looking very nice. The six screws are arranged so the top cover braces the front and rear panels, preventing the disturbing flexing that occurred when we examined the first unit. Unfortunately, self-tapping screws were used, and these were already spinning a bit in their holes before our experiments were done. Soft materials will do that, which is why plastic and soft metal panels in cars and machinery often include those little spring-steel clips for catching the screw threads.

The interior layout is very clean. The total separation between the high and low-voltage sides is exactly what we want. The transformer looks to be good quality and the fuse holder is definitely being used.  The ground wire is actually connected to something, an otherwise frequent oversight in direct-import kit. Even better, it is attached to the chassis and a transformer leg at a single point, where it should be. On the low voltage side, the wiring is clean and bundled, the PCB layout is spacious and thoughtfully designed even if the material seems a bit cheap, and there is plenty of insulation, even on parts that don’t necessarily require it. Someone planned this layout instead of just throwing things together.

Regulator in new supply

Welcome to the regulator side.

The problems emerge in the details. On the low-voltage side, complaints are minor. The red multi-way terminal is visibly deformed. A power resistor operating at high temperature is mounted on the PCB instead of being well ventilated elsewhere, although it is mounted high and won’t bake components above. Useful vent holes on the bottom were drilled in exactly the place where the transformer body blocks them, making them useless. And the more disturbing thing was the discovery of a few poor solder joints on the PCB. These would have eventually failed, and that repair led to a second discovery: the wiring on the low voltage side is copper-coated aluminum.

Copper-coated aluminum is solely a cost and weight-saving measure. It can be tolerable in some low-voltage applications where things never move, but it doesn’t meet formal electrical standards in many jurisdictions and is mechanically weak. Just try offering a box of mysteriously cheap, off-name plenum cable to a network professional who has seen the stuff before. We thought about doing so as a side-feature for this review but didn’t want to risk being stoned to death with Mountain Dew bottles.

Fortunately, the mains power cord turned out to be actual copper, so no black mark there. Instead, we found something stranger. The cord employed the IEC color scheme of brown, blue, and yellow/green, but the blue wire turned out to be connected to the hot lead from the mains. Even more strange, the blue lead was correctly wired (deliberately, or otherwise) to the fuse holder. Unfortunately, the output from the fuse did not go to the switch. Instead, it was tied to the transformer, the transformer output went to the switch, and the switch then returned to the mains neutral using the brown conductor.

And what does give it a genuine black mark is that the ground, though present, was tack-soldered to a terminal. A proper ground lead must be compression crimped into a suitable ring terminal. The reason is that in a worst-case failure, high currents could flow through the ground long enough to loosen the solder. The ground lead should be the very last thing to go as the entire device is burning to the ground, and only a compression crimp guarantees that level of endurance.

New supply ground

Not quite grounded in reality.

If the internal color swap with otherwise correct polarization had been the only thing wrong, we could have at least rated this “not dangerous” while still noting the other issues. But a switched neutral is poor practice and the tack-soldered ground is a definite “no.” We appreciate the effort that did go into designing this device correctly but in the end, it lost its passing grade on a couple critical points.

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Aaron Vienot

Engineer by day, hobbyist by night, occasional contributor, and full-time wise guy.

35 Comments
    • cegras
    • 3 weeks ago

    Great article!

    Reply
    • LiquidSquid
    • 3 weeks ago

    Thanks for the trip down memory lane. I have a few of these 13.8V supplies around (Car battery voltage for running HAM equipment and other car related crap)
    What is cool is a tiny SPS wall-wort for $10 can have more output power than one of these behemoths, and is much safer and far more power efficient. However, the SPS will also be far more noisy as far as electrical noise.

    Reply
      • ludi
      • 3 weeks ago

      Indeed, although the attractiveness of a bench supply is that the power switch and terminals are Right There for attaching whatever. The coworker I referenced in the video segment is squarely in the millennial generation and had somehow turned up one for hobby use, so that’s a pretty good sign that these things are as popular as ever among the DIY crowd.

      Reply
    • dragondaddybear
    • 3 weeks ago

    I love the dual post style. Also, I really love the humor.

    Reply
      • juzz86
      • 3 weeks ago

      Me too! Good job ludi, a great read mate!

      Reply
    • continuum
    • 3 weeks ago

    Slightly off-topic question, what’s with the grey text in parenthesis after the links? Is it some attempt at WCAG 2.0 compliance without proper tags in the CMS? Or some attempt at footnotes without actually doing footnotes? Just curious since I’ve never seen a site do that before…

    Reply
      • Ben Funk
      • 3 weeks ago

      It seems to be a way to differentiate a real link from an automatic one.

      Reply
        • ludi
        • 3 weeks ago

        Bingo. It also gives mobile users an easier way to determine if they want to visit the link, since mouse-hovering isn’t implemented as conveniently on a touchscreen.

        It may or may not be used [ever again / by any other authors / cheese ], but I thought I would try it out as an experiment.

        Reply
    • willmore
    • 3 weeks ago

    Before anyone says it again, at the voltages you’re going to find in low voltage sides of these boxes, the caps aren’t going to give you any shock at all. Now, in a modern switching mode power supply, the front end caps can have more than 2x peak AC voltage on them which is around 340V. That will gladly kill you.

    Reply
      • ludi
      • 3 weeks ago

      Yep. And as it happens, both designs in the article (and all three designs shown in the video feature) are constructed such that they bleed down pretty quick when shut down. Since neither I nor the TechReport could invest the proper resources to discuss all possible hazards illustrated in this review, we opted to cover it with multiple, plainly-worded, “don’t try this at home” disclaimers.

      Reply
    • willmore
    • 3 weeks ago

    Can you get some close up shots of the control board and pass transistor for the older power supply? We can probably pull some date codes off of there. Can you see what value the large resistor on the output is? It’s likely a shunt for overcurrent protection. I’d be the control board has an LM723 on it.

    Nice teardown–now on to the new design…

    Reply
    • DPete27
    • 3 weeks ago

    “See how I just nonchalantly fingered the solder terminals on the bottom of those larger capacitors without verifying that they’re discharged (or stating this step had been done prior)…don’t do that”

    I applaud the video content and i think it’s a strong start in the right direction. If I can offer any constructive criticism (no offense intended) it would be to spice up the delivery of the [admittedly dry] review content from the speaker. The effects were a welcome addition to keep things lively, but [IMO] the idea is to make this [boring] power converter sound like the coolest/funnest thing on the planet.
    Obviously most of us Millennial+ viewers are turned off by the LTT-style of delivery, but remember that Gen-Z is responsible for probably an order of magnitude more views and likes comparatively. I’d say that LTT generally doesn’t have the most in-depth or insightful content, but their STYLE of delivery is what attracts views in droves.
    I don’t have the answer whether to go full psycho on the video content in order to cater to the younger crowd while allowing the written content to continue drawing readership from the older generations, or if there’s a happy medium that can be struck.

    Reply
      • ludi
      • 3 weeks ago

      If that’s what you think people want, I’ll wait for you to make that video 🙂 It’s harder than it looks.

      Reply
        • DPete27
        • 3 weeks ago

        I absolutely agree.

        Reply
    • chuckula
    • 3 weeks ago

    Bonus safety tip since I see a nice big blue capacitor in there: Capacitors often hold substantial charge if you turn off the power supply without discharging them.

    So you need to watch out for a scenario where you run the power supply, fully disconnect it from the wall, and still have to worry about the potential for getting a nasty shock if you open it up to do work without making 100% sure the Capacitors are discharged

    Reply
      • dragondaddybear
      • 3 weeks ago

      When I was younger that was an evil trick I would do. I’d hand a charged cap (using a transformer and a battery to charge it) to someone and shock them. It was a take on the sock box I did in school. Very appropriate/fun/evil way to learn electron flow, basic circuits, and transformers.

      Reply
        • crabjokeman
        • 3 weeks ago

        We used to play “pass the capacitor” in lab, where we’d soft toss around an electrolytic capacitor and try to catch it by the cover to avoid getting shocked.

        Reply
    • chuckula
    • 3 weeks ago

    Sweet article and finally some subject matter on TR that can get you killed if you don’t do it right!

    Reply
      • Krogoth
      • 3 weeks ago

      “Our shilling can’t repel potential of this magnitude!”

      Reply
    • Krogoth
    • 3 weeks ago

    Unlimited Power!!!!!!

    Reply
    • redocbew
    • 3 weeks ago

    OMG WHO IS THIS WTF SO SAD

    Reply
    • usacomp2k3 (AJ)
    • 3 weeks ago

    Enjoying the read so far. Does Aaron have a forum handle that we recognize?

    Reply
    • In the video he clarifies that he’s ludi—as well as in the comments yesterday where he accidentally doxed himself, lol.

      Reply
        • ludi
        • 3 weeks ago

        Aaron? Never heard of him. *flips trenchcoat and scurries off*

        Reply
        • Can one of the mods ban this joker for running multiple accounts? 😉
          Seriously though, thanks for your work on this, it could be life-saving information and will directly impact my future purchasing decisions (in a good way).

          Reply
          • usacomp2k3 (AJ)
          • 3 weeks ago

          Great job sir! I really enjoyed the rest of the read. My dad’s dad was a big electrical hobbyist (worked for Ma Bell back in the day) and while the curiosity is genetic, the skill is not. It’s still somewhat black magic to see someone understand what’s going on.

          If you’re even in the Orlando area, you’d love Skycraft (https://www.skycraftsurplus.com/). They have all sorts of vintage electronics like old Agilent Oscilloscopes.

          Reply
            • ludi
            • 3 weeks ago

            Thanks!

            My dad is a lifetime electronics technician and also a hobbyist. I had the early advantage of learning a lot from him early in life, including proper soldering technique, and then went deep into DIY audio around 15 years ago. There are also a lot of good YouTubers that enjoy delving into electrical equipment, which is a great teaching shortcut that didn’t really exist 10+ years ago.

          • Mr Bill
          • 3 weeks ago

          Well written, useful, interesting, and humorous… [quote]We thought about doing so as a side-feature for this review but didn’t want to risk being stoned to death with Mountain Dew bottles.[/quote]
          You should write reviews more often.

          Reply
            • ludi
            • 3 weeks ago

            Sadly, I don’t tax my computer hardware as much as I used to, and that gives me less relevant material in which to geek out. The video editing and encoding for this review was the hardest I’ve worked my main desktop system in over a year, and my last from-scratch system build was a low-end Skylake HTPC nearly three years ago.

            If TR sticks around for a while and I find something interesting, I’d be open to doing it again.

          • Aether
          • 3 weeks ago

          Great lunchtime read; thanks!

          Reply
    • Captain Ned
    • 3 weeks ago

    The traditional “brand name” for inferior Chinese-sourced components is “Yum-Cha”.

    Reply
      • ludi
      • 3 weeks ago

      Interesting. I’ve been heavily into DIY electronics for a while and hadn’t heart that slang yet.

      Reply
        • ludi
        • 3 weeks ago

        *heard

        Reply
        • GhostofNappa
        • 3 weeks ago

        I’m not sure what this Yumcha is, but it sounds like a Raditz to me.

        Reply

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