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A component of a board from an appliance has failed and I would like your help identifying it, in order to replace it.

Below is a picture from the board, the arrow points to the failed component:

photo of PCB

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    \$\begingroup\$ How do you know that it's died if you don't know what it is? What's on the other side of the board at that location? It looks to me as though something on the other side has been overheating. \$\endgroup\$ – brhans Aug 21 at 21:56
  • \$\begingroup\$ The reason I believe it has died is the black mark on the board, like it has been fried. There’s nothing on the other side. Just a couple of resistors near it. \$\endgroup\$ – Christos Polydorou Aug 21 at 21:59
  • \$\begingroup\$ If your post included details on what the "appliance" is and what you think the circuit board does it may help. Please post the details into your question, not in the comments. \$\endgroup\$ – Transistor Aug 21 at 22:16
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    \$\begingroup\$ Gotta love the fusible traces on it. :) \$\endgroup\$ – rdtsc Aug 21 at 22:40
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  1. I'm not convinced that the surface-mount device (resistor?) pointed at with your red arrow, has necessarily failed. Yes, something in that approximate area has got hot, but that doesn't mean it was this SMD.

  2. If you reverse-engineer that part of the PCB and draw the schematic (assuming you can't get a schematic any other way), this would help you to understand more. For example, I've marked the location of a through-hole component with a light-blue line on the edited version of your photo below. That component seems to be in parallel with the unidentified SMD component. That would be odd, if both components were resistors, so at least one of those two parallel components is probably something else.

    Edited close-up of part of the PCB, from the original image in the question

    The PCB may have got hot in the area of that through-hole component, rather than the SMD component next to it. If I was trying to diagnose that PCB, I would be drawing a schematic of the part of the PCB, to help with understanding the design.

  3. The main reason I wanted to write this answer, was to highlight this point: It seems that at least one relevant solder joint is "dry", perhaps actually now loose (fractured) and therefore either high-resistance and/or intermittent. I've marked it with a solid green arrow on the edited copy of your photo above.

    That "crescent" of darkness you can see in the solder joint, is classic of that type of problem. Notice how the suspect solder joint is very "crystalline-looking" - compare that with the shiny solder joint below it. Many repair engineers would reflow all suspect solder joints on a board like that.

    Therefore it's possible that:

    • no component has actually failed;

    • the suspect solder joint is the actual cause of the problem;

    • the PCB has got hot due to high current going through the higher-than-normal resistance of that suspect solder joint, to whatever is connected to the black wires on the right of your photo in the question (I'll guess perhaps some kind of motor?).

    Obviously component failures are also a possibility. However no component values can be identified from the photo you supplied.

    Someone in front of that actual PCB would need to investigate further, to see which solder joints are faulty, and which components (if any) have failed. Since this is a mains-powered device, please be very careful if you decide (at your own risk) to do any troubleshooting - both because of the potentially-lethal voltages, and also in case something mechanical (e.g. a motor) suddenly and unexpectedly moves, while your hands or face etc. are close to it. If in doubt, contact someone local to you who is qualified / experienced for this type of work.

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    \$\begingroup\$ Christos - FYI repair questions are not usually on-topic here, unless you provide "design-level" information e.g. a schematic diagram. I know you asked this as an "identification" question - I'm just letting you know, before this question goes too far in the direction of a repair question. \$\endgroup\$ – SamGibson Aug 22 at 0:08
  • \$\begingroup\$ Thank you for your help Sam! \$\endgroup\$ – Christos Polydorou Aug 26 at 7:21
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It doesn't look failed to me. It's a thin film resistor with no top. There no way to determine if it should have a black epoxy top or not without seeing a part number, working unit or schematic.

If it did fail, then it's likely that the value has changed, finding another unit will be necessary to determine the value.

Usually when resistors fail, they also show signs of heat damage on the part (which is not apparent in the pic above) and\or on the PCB below. There are also PCB trace fuses on the PCB and they are intact.

High Power Thin Film Wraparound Chip Resistor

enter image description here
Source: http://www.vishay.com/docs/60076/php.pdf

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  • \$\begingroup\$ It probably should have a black top like the nearby one. It just blew off the top, I think. \$\endgroup\$ – jonk Aug 21 at 23:57
  • \$\begingroup\$ Some thin film resistors come 'out of the box' like that. The resistors that I have seen blow their tops don't look as clean as that one does. \$\endgroup\$ – Voltage Spike Aug 22 at 1:34

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