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Thread: PSU heatsinks electrified?

  1. #21
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    Quote Originally Posted by jayjr1105 View Post
    Measured -165v DC and 123v AC across those heatsinks. The secondary side heatsink acts like a ground. Same result when probing black lead to the chassis.
    That's a strange meter with both AC and DC voltage on the same selection; how does one switch between settings?

    meter.jpg

    As well as replacing the capacitors (which you have already done), you might want to consider oiling the fan.
    Last edited by ashiekh; 03-09-2019 at 11:29 PM.

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    Quote Originally Posted by asf14tomcat View Post
    Rm1000x . Pfc heatsink connected with (-) 380vdc . They add small resistor (0 ohm) between them
    Still need a picture? . I have some 1000x dead in my room
    Please do. I can't check myself until Monday (if I'm not too busy). If I'm wrong, I'm wrong. Wouldn't be the first time.

    Is it just the RM1000x or do you have others?

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    I've been wrong more times than I can remember; it is the route to getting things right.

    This is turning into a most important thread, in that it involves safety.
    Last edited by ashiekh; 03-10-2019 at 11:12 AM.

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    Quote Originally Posted by jonnyGURU View Post
    Please do. I can't check myself until Monday (if I'm not too busy). If I'm wrong, I'm wrong. Wouldn't be the first time.

    Is it just the RM1000x or do you have others?
    Not only 1000x . sea fsp sama is same . we talk about safety reason . yes this is safety .
    4944becb5ff2bdace4e3.jpg
    3a69cd713448d6168f59.jpg
    db1de70d1e34fc6aa525.jpg
    I remember one or maybe two cheap unit I have repaired in the past isolate the Heat sink with high voltage ( not grounded)

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    Jon Gerow (03-09-2019)

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    Quote Originally Posted by asf14tomcat View Post
    Not only 1000x . sea fsp sama is same . we talk about safety reason . yes this is safety .
    4944becb5ff2bdace4e3.jpg
    3a69cd713448d6168f59.jpg
    db1de70d1e34fc6aa525.jpg
    I remember one or maybe two cheap unit I have repaired in the past isolate the Heat sink with high voltage ( not grounded)
    Good to know. I'll research further.

    FYI:

    http://www.giangrandi.ch/electronics.../smpsfix.shtml

    "Keep also in mind that heat sinks very often are not grounded and they can very well be at mains voltage."

    Note "very often" and not "always".

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    Quote Originally Posted by Stefan Payne View Post
    I don't want to open the HXi
    I just realized one can test if a heatsink is grounded without opening up the unit; one can often get a DMM probe to touch the heatsink through a vent and them find the resistance to the case and compare this to when the leads are shorted. This must be done on the unpowered unit and I cannot be held responsible for any damage that might result (the capacitors might still be holding charge).

    DO NOT USE THIS METHOD ON A LIVE POWER SUPPLY.

    Do not do this unless you know exactly what you are doing and are willing to take responsibility for your actions; if you think I am exaggerating the dangers then it is best you don't try.

    https://www.dailymail.co.uk/news/art...-computer.html
    Last edited by ashiekh; 03-10-2019 at 12:20 PM.

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    The PSU wasn't plugged.
    probably the bleeder failed.

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    Quote Originally Posted by ashiekh View Post
    I just realized one can test if a heatsink is grounded without opening up the unit; one can often get a DMM probe to touch the heatsink through a vent and them find the resistance to the case and compare this to when the leads are shorted. This must be done on the unpowered unit and I cannot be held responsible for any damage that might result (the capacitors might still be holding charge).
    This sounds like a horrible idea. LOL!

    The vent holes are so small. Yes, a probe easily fits through them, but getting the probe to touch the heatsink and not touch the surface of the housing would be like playing a game of Operation.



    Though I suppose you could use some insulated probes with just an exposed tip, but I'm not sure I have a set.

    I'll play with this on Monday if I have time. I'm not so much curious as to IF the heatsinks are energized right now. I'm more inclined to find out WHY. What part does it play in the design. What's the benefit?

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    Quote Originally Posted by jonnyGURU View Post
    What's the benefit?

    Better thermal contact?

    I had no problem measuring resistance with the supply off as there is no issue if one slips; I tried on a few supplies I had sitting around.

    I do NOT suggest this approach to measure the voltage.
    Last edited by ashiekh; 03-10-2019 at 05:26 PM.

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    Quote Originally Posted by jonnyGURU View Post
    I'm not so much curious as to IF the heatsinks are energized right now. I'm more inclined to find out WHY. What part does it play in the design. What's the benefit?
    It's an EMC reason. The heatsink has to be tied to a static potential (either positive or negative), otherwise higher common mode currents will be built up because of an higher stray capacitance to earth. If it's better to connect the heatsink to the positive or negative DC link voltage depends on the used topology. It makes a difference for flyback converters as the high voltage DC link node with the heatsink connected can be used to add stray capacitance to the transformer which can help for EMC.

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