I think I broke a SMD diode on my Leopold FC750R PD. Would appreciate it if someone can help me find the correct replacement pt#. [help]

TLDR: Hoping someone can both double check my logic here and recommend a replacement part # (and a place to source it if you’re feeling generous) for the SMD diodes used on this board (FC750R PD).

Full story: I am working on a board for a friend and desoldered the old switches and soldered in new switches yesterday. After I finished up (but foolishly not before I started) I used Switch Hitter and Aquakeytest to check the board. I saw that R-Windows and R-Ctrl were not working. I realized there is no R-Windows because it’s the Fn key on this board but that didn’t explain R-Ctrl. I checked the switch with multimeter and confirmed it was working. I was worried I lifted a trace at first but after scratching my head for a while I determined that I most likely broke the diode for R-Ctrl carelessly at some point. In retrospect it’s fairly obvious because it looks visible different than the other working diodes and I was able to get R-Ctrl to active by bridging past it to the switch traces with some tweezers.

I threw a couple annotated images together of the PCB, the diode in question, and the traces for R-Ctrl to explains some of the troubleshooting I’ve already done (https://imgur.com/a/5zMXsgB). The diode in question is D59.

I already purchased these diodes off amazon based off some googling and searching in this sub (link). Based on my research I was looking for 1N4148 in an SMD package. The product from amazon linked above says its a “1N4148W” in a SOD-123 package. I’m not sure what the W designation at the end means. The package size is different from the diodes on the board (larger width and height, but very close length), but the dimensions are close enough that I think it should fit on the traces. Could anyone confirm/deny that these going to work for me? If not, what is the appropriate diode? I ordered off amazon because I promised my friend his board back a week ago and I’m still not done with it because because I’m good for nothing and I wanted to get back to him ASAP.

I’m guessing those are 0805’s (imperial, 0.08 x 0.05 inches) but your length seems to be off by a bit, and SOD packages are not as flat/rectangular from my experience. I’d recommend redoing your measurements in inches and searching for a diode that matches. The specific part number doesn’t really matter much.

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If there is only the key with the diode that don’t work then that means that no MCU IO pin has been fried, you are lucky guy :slight_smile:

As said @hadi SOD123 and the supposed 0805 footprint on your board are not the same… but if the pins of your SOD123 diode more or less land on the PCB pads then you should be good to go.
It will not be the prettiest repair but hey if it works it works.
1N4148W reference is ok, don’t bother with the W :wink:

Now you will first have to desolder the fried diode before soldering the new one.
It is rather easy when you know how to do it … and you can detroy tracks or lift pads if you don’t (I know that by experience :smiley: )

Method 1(prefered):

  • use a hot air soldering station.

Method 2 with an iron:

  • use the biggest iron tip you can have.
  • put as much solder on it as you can.
  • heat the component trying to heat as much of the component side surface as you can, ideally both pads if your tip allows it.
  • both solder pads solder should melt and your component should gently slide away.

Here is a video that more or less show the process:

If you are super lazy and don’t care about how the repair looks you can use a through hole diode. Don’t even need to desolder the bad one so long as the positive leg connects to the positive pad and same for negative. Once it’s attached just bend the diode over and apply electrical tape if you think there is danger of a short anywhere.

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It’s dirty as hell but the easiest to do if you have a though hole 1n4148 laying around :smiley:
Just be sure the broken diode is not conducting current anymore.

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Thanks for the help @hadi, @rico, and @rpiguy9907

I managed to get the old diode off with a soldering iron, some copper braid, and no small amount of perseverance. I got the SOD 123 diodes in the mail and manged to get a new diode soldered on the pads (messy as hell) in the correct direction after checking the checking the orientation with a multimeter. The R-Ctrl key now registers properly!



One more keyboard saved :slight_smile: