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DVR power supply testing

Discussion in 'Troubleshooting and Repair' started by Ed Sowell, Sep 5, 2018.

  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It doesn't look like that resistor has gotten hot in service, and eventually failed. I suspect it failed all of a sudden due to a massive overload.

    I would be checking for semiconductors that have failed short circuit.

    If this resistor happens to be a gate resistor for a mosfet, then I would be expecting more failures than just the mosfet and this resistor. However it looks like a wirewound resistor, and that's not what would be used in that location.

    If you're really keen, since it's open, find a replacement, solder it in the copper side (that will be easier) and see if it fails.
     
  2. H2814D

    H2814D

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    Nov 4, 2017
    Ed...I think you better start working on those soldering skills if you want to get this thing working again. :)

    Any chance you had a lightening strike near the time of failure? Does that power supply have a fuse anywhere? Is it blown? (Don't just put another fuse in there and hope that works. You may damage more stuff.) If so, a good chance several components will need to be removed and tested to troubleshoot the problem. Like those three legged black things (power transistors) attached to those heatsinks; THAT CAPACITOR THAT NO ONE ELSE SEES A BULGE IN :); That purple resistor with the possible burn mark.

    Once you remove the components, google the numbers/letters on them so you can know what you have (or ask here) and then search youtube for the proper testing procedures. You can do this. If nothing else, it has now become a challenge. :)
     
  3. Ed Sowell

    Ed Sowell

    37
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    Aug 1, 2016

    It appears to connect to the black rectangular transistor mounted on the adjacent aluminum heatsink.

    I'll do that, assuming I can identify it. It looks like the markings are partially obliterated. I have a good electronics store nearby that might be able to help.
     
  4. Ed Sowell

    Ed Sowell

    37
    3
    Aug 1, 2016

    I've done a few board component replacements over the years so I'm pretty sure I can do the resistor at least. Oh, and I've watched some YouTubes on capacitor replacement so I close to being certified, right?:)


    No lightning. However, this all began with a failed heatsink fan on the DVR motherboard. The fan shaft broke at some point, and I suppose it's possible that the motor armature got jammed. Not sure that would do it.

    No fuse.


    I have begun to see this as a challenge, so I might pursue it to the (hopefully not bitter) end. However, If I do find a replacement for the PS I'll probably go that route to get the security system back in service.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It might help if you can take a good photo of that.
     
  6. Ed Sowell

    Ed Sowell

    37
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    Aug 1, 2016
    A friend with more experience in this stuff has offered to take a look at the PS for me. I've asked him to send me a photo of the burned out resistor when he gets it off the board.
     
  7. Ed Sowell

    Ed Sowell

    37
    3
    Aug 1, 2016
    here it is

    BadResistor.jpg
     
    Last edited by a moderator: Sep 21, 2018
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
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    Ignore that resistor for a moment.

    You mention it connects to a transistor at one end. I suspect the other end connects to an IC. Get a good picture of both. They need to be good enough that we can read the markings and preferably see all the dust and dirt on the device. We'll be looking not only for what they are (from the markings) but for indications that either or both have failed.

    Next we should b able to tell you how to test the transistor, but if they're cheap enough I would be replacing the transistor and the chip and hoping that's enough to get it operational again (oh, and of course, replacing the resistor).

    There are also some passive components that I'd be testing and I'd be replacing the output filter capacitors regardless of whether or not they looked damaged.

    Also be prepared to order from a specialist parts seller to ensure you get quality parts -- and hope they're all still available.
     
  9. 73's de Edd

    73's de Edd

    2,678
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    Aug 21, 2015
    Sir Ed Sowel . . . . . . . ( my Mom upgraded . . . . .and got me the extra " d " back on day one )

    I also am seeing no pooch-out or distortion of the center E-caps cross scoring . . .I believe that it is just a lighting aberration / reflection cause.
    STILL looking for your fuse up in the corner where the AC power comes in.
    I concur in that now open 0.56 OEM metal film resistor to be associated with the power device on the other side of the heat sink. Need to know what that unit is . . .be it a power FET 3 leads . . . . or a custom power IC with electronics and POWER FET included. Which will use more than 3 leads.
    Your units electronics uses the 12vdc supply WHILE your outdoor cameras frontal IR LED cluster uses the 52VDC supply portion.
    VERY interested . . . . . in how that device ohms out between its connections possibilities.

    " If this resistor happens to be a gate resistor for a mosfet "
    maybe in series with the drain or source . . . .but I wouldn't expect that low of resistance and hefty of a wattage to EVER be used with a mere FET gate.

    73's de Edd
    .....
     
    Last edited: Sep 15, 2018
  10. Ed Sowell

    Ed Sowell

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    Aug 1, 2016
    I want to report success! Here's a summary, based on what my volunteer circuit guru told me:

    The original problems were identified as a visibly blown 0.56 Ohm resistor at R355. Continuing though the circuit, the MOSFET Transistor at Q351 (W9NK90Z) was bad. These tested bad from the beginning. After replacement, there was 52 volts and 12 volts on the vertical PCB, but the voltage was not being sent to the wiring harness outputs. Other transistors were removed and tested, with not much help.

    Still dealing with incorrect voltage at one of the outputs, another visit to the forum led to replacing the IC(CM6800UBX) on the vertical board, sourced in China. That was the last problem! Apparently, it had gone out along with the Q351 MOSFET and the 0.56 Ohm resistor. With all PS voltages now correct, the system worked perfectly after reassembly. I was a happy camper indeed when the display lighted up with "Lorex," and images filled the screen with images, one after the other, as I cautiously plugged the cameras in one at a time.

    Yet, one has to wonder how long it will last. If the original problem was failure of the processor fan, it's going to happen again since the replacement fan appears to be exactly like the OE. So, I'm now thinking about an upgrade. Haven't found it yet, but there must be a higher quality one out there somewhere. I'm thinking steel shaft, ball bearings, and quiet.

    There's a photo earlier in this thread showing the OE fan on the board. Basically, it's a 45x45mm, 12v, 2-wire heatsink fan with outboard tie-down pins. I believe it was commonly used in laptops, DVRs, etc. a number of years ago. From the photo, you can see that a larger one could be fitted using the 4 other post holes, seen about a 1/4" farther out... about 50mm center-to-center. If anyone can suggest a source of a quality replacement, I'd appreciate it.

    Many thanks to all in this discussion.

    Ed
     
    (*steve*) likes this.
  11. Ed Sowell

    Ed Sowell

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    Aug 1, 2016
    Oops. This fan photo in in my thread "lorex-dvr-what-is-this", where this not is also posted.
     
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