This is a picture of a circuit board inside my elliptical trainer. It has a built-in fan that has not worked for a few years. I thought it might be a slipped belt, fuse, or something otherwise straightforward to repair. What I found instead was the burned surface mount transistor (Q5) that I identified with the red arrow on the right side. The fan is controlled by a small momentary contact switch on the other side of this board. I suspect that Q5 was used to latch the fan's supply voltage on and off.

The picture makes this transistor look larger than life. It's smaller than anything I've tried to solder. Based on what's left of the markings and the nearby transistors, I believe that it's a D882 NPN medium power type. This component seems a little undersized to act as the relay for a 14 VDC motor, but it's the only visibly damaged component. The rest of the trainer's functions operate normally.

I could try to desolder this tiny thing and replace it. It's not difficult to find it at Amazon and Mouser. I have also found it in a larger, non-surface mount package that looks much easier to work with. So there's a chance that I could wire-splice in the replacement and leave the burned one in place. That might fix it, if the part is not shorted. Since the fan doesn't turn, that seems posssible.

Of course, another option would be to leave the broken part alone and use a separate fan (as I have been). Maybe I'm being compulsive...

Any advice? I have a decent thermally controlled iron and know how to use it, but I haven't needed surface mount chops until this.

Many thanks!

Scott C. in Cary, NC

 

Transistors in this package size are actually quite easy to replace. If you have had any soldering experience you shouldn't have a problems doing this. Solder wick is the right choice for this.

But the real question is why did the original burn out? You probably should check the fan motor for functionality.

 

Any advice? I have a decent thermally controlled iron and know how to use it, but I haven't needed surface mount chops until this.

Personally, I'd use a hot air tool or soldering iron tweezers as shown below:

The problem you're going to have with a soldering iron is that you need to get the solder on all three leads melted at the same time. You could use low temp solder to keep the solder melted longer, or try to lift the leads individually. But the right tool will make the job easier.

 

hot air all the way. takes about 5-10 seconds to remove that one and place another on

If you only have a regular iron and no hot air then cut the legs with razor and wick clean the area, you can also glob solder over the top until it covers all three legs, it works but more to clean up. The new component will go down easy enough with just a regular iron and clean pads to work with.

 

Use solder wick to remove most of the solder from the single pin. Now heat the single pin while using a toothpick or other pointy object under the part and lift slightly so that the single pin is clear of solder. Now heat the other two pins at the same time and lift the part off the board. Clean up with solder wick.