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Decided I would try and fix the remote for this 3 speed fan I have a home since it is summer now. Here's the circuitry I'm dealing with here:

enter image description here

So here our are some notes:

  • There was some battery leakage when I opened it up, but I cleaned the battery contacts. Would this be harmful to say the ceramic resonator or capacitors?
  • I replaced the IR bulb with no luck (in the right orientation)
  • All contacts look good, nothing looks like it burned up

My next move was to replace what I think is a fuse below that NPN transitor. Can anyone confirm that little red thing is indeed a fuse? If so, I have a bunch of these standard green ones lying around that I could put in.

EDIT:: Here's the bottom: enter image description here

codebender
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    No, that's a diode. Did you measure voltages? – Ignacio Vazquez-Abrams Jun 25 '15 at 15:23
  • Yes so its showing 2.8V for the two AAA in series, seems fine right? – codebender Jun 25 '15 at 15:31
  • There are far more voltages in the circuit than just from the batteries. – Ignacio Vazquez-Abrams Jun 25 '15 at 15:32
  • Yeah, definitely a diode, 1N4148-ish looking. – John D Jun 25 '15 at 15:33
  • Show the other side of the PCB: The remote must have an IC somewhere, probably a plastic blob (a COB or chip-on-board package), which decodes the buttons and modulates the IR LED. Also, does the LED light up when you press the buttons? You can use a camera to see the IR light emitted. – jms Jun 25 '15 at 15:33
  • @IgnacioVazquez-Abrams ah I like your thinking. Well I'm getting about 300mV over the LED, Nothing over the resisors or the resonator or the tiny capacitors, and 2.8 over the 47uF cap.

    Its hard to measure the effects of button presses in its form factor unfortunately.

     – codebender Jun 25 '15 at 15:46
  • There isn't much on that thing. If there's a chip on board on the back, then there's a chance a trace broke there when the board flexed (dropped, stepped on, etc.) I've also had the resonator (the yellow thingy) quit after a remote was dropped. Without a way to test things, we're just shooting in the dark, here. If you want to try replacing the yellow thingy, it is a 455kHz ceramic resonator. Even Amazon sells them, so it shouldn't be too hard to get a replacement. – JRE Jun 25 '15 at 15:50
  • If you replaced the red diode, then did you pay attention to which way it went in? The black stripe is important, it tells you which way it needs to go. – JRE Jun 25 '15 at 15:53
  • @JRE ya luckily the trace tells you orientation, and remember the fatter end of the LED being the negative side.

    I'll try and replace the resonator though, it probably has suffered a few drops as well :)

     – codebender Jun 25 '15 at 15:57
  • The little red thing shouldn't just be replaced if you can avoid it, unless the PCB gives a type number, what with it also possibly being a zener or special curve glass diode. Most likely is a 1N4148 or 1N4444 or some such, but without proper testing and/or type number and/or schematic one cannot be sure enough to just simply replace it. – Asmyldof Jun 25 '15 at 16:21

2 Answers2

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The "little red thing" is a diode. Without physical evidence of damage, it's probably fine.

Nick Johnson
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Battery leakage typically just corrodes the battery terminals. If it leaks onto the circuit board and gets between pins of devices, it could cause some issues but that is rare. Isopropyl rubbing alcohol and a small brush or cotton swab will usually clean it up very well.

The "IR bulb" is an IR LED, and appears to be wired correctly. But where did this replacement come from? There are literally a million different types of LED's; getting an exact match can be quite difficult. Generally, they don't "burn out" the way a traditional bulb would, so there is very little chance the original is defective unless it is broken, melted, or burnt-looking (or smelling) in any way.

Is the new LED soldered correctly?

A tip: try pointing the remote at any modern type of video recorder (such as a cellphone) and press a button. Modern (CMOS-imager based) video recording devices are usually sensitive to IR, so if the circuit it working, you should see the LED light up on the recording. An example of a remote being visible by webcam can be found here.

rdtsc
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  • Ya it's not lighting up, I could try putting the old one back it.

    But neither would work if the resonator gave out right? I'm going to try replacing that first.

     – codebender Jun 25 '15 at 15:55
  • Unfortunately the cell-phone requires qualification. Response to a 1A/1.6V IR power LED (850nm, not even the 930nm standard) for many Samsung and iPhone models is negligible even in low light (others remain untested by me), due to a built in IR filter, so I can imagine a normal 5mm LED not showing up at all on those. Cheap is what to look for: No budget for optical filters. Most Logitech WebCams also have IR filtering. – Asmyldof Jun 25 '15 at 16:18
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    I duly qualify my comment with the following evidence. A Samsung Galaxy 4s is also capable of picking up the emissions. While I do not have an arsenal of devices to test this against, I stand by my comment that many CMOS imagers are sensitive to IR, and could work for this purpose. A more definitive measuring device would be an IR Test Card. – rdtsc Jun 25 '15 at 17:13