Tombstone Brings New Life To Board

Making revisions to existing PCBs with surface mount components often leads to creative solutions, and this insertion of a switch over a tombstoned resistor is no exception. According to [kubatyszko], “this is an FPGA-based Amiga clone. R15 serves as joint-stereo mixing signal between channels to make it easier on headphone users (Amiga has 4 channels, 2 left and 2 right). Removing R15 makes the stereo 100% ‘original’ with fully independent channels. Didn’t want to make it permanent so I decided to put a switch.”

Whether [kubatyszko] intends it or not, this solution is not going to be permanent without some additional work to mechanically secure the switch. We’ve tried this sort of thing before and it sometimes results in the contact area of the resistor being ripped off the substrate and separated from the rest of the resistor, rendering it useless. However, the creative use of the pads to get some additional functionality out of the board deserves some kudos.

We love creative fixes for board problems but it’s been a really long time since we’ve seen several of them collected in one place. We’d love to hear your favorite tricks so let us know in the comments below.

24 thoughts on “Tombstone Brings New Life To Board

  1. I sometimes do this sort of thing when I don’t have the right SMD resistor at hand. When you need two resistors to get th desired value, you can just have them touch in the middle. Three means that you get to build a kind of SMD Stonehenge.
    For more than that, it’s easiest to first solder rows of a few together on the back of some scrap FR4. You can use Kapton to hold them in place while soldering and to position them properly. This works best if you have a gap of about 6mil.

  2. An alternative solution that’s less susceptible to mechanical stress is to use fine gauge wire wrap wire. I use 30AWG wire wrap when validating my prototypes or implementing fixes or minor design changes…makes connecting traces, component leads, or test pads to the scope or logic analyzer much easier, too.

    1. 30AWG Kynar is the de-facto standard bodge wire, and the light blue variety is responsible for the alternate term “blue wire”.

      However I’ve recently switched to using salvaged magnet wire where abrasion resistance isn’t a concern.

  3. OK, I’m confused. Why in the world would you do it this way?

    There’s plenty of board space beside them. Turn the resistor 90 degrees, soldering it to only 1 pad. Flatten both of the leads of the switch. Solder one switch lead to the switch, turning it at an angle so it doesn’t interfere with the resistor. Then solder a wire jumper between the other leg of the switch and the other end of the resistor.

    Now both components have at least one leg soldered to a pad, and are flat on the board, and you can epoxy down the other leg of the switch so it’s not putting torque on a joint.

  4. Hot glue and wirewrap wires are my friends too… I would have glued the switch down somewhere and connected a wire to the tombstoned resistor and pad. At least for something that needs to get switched a few times, this is much better than having a half broken resistor or solder joint that messes up your circuit without any visible clue. Finding these errors/failures can cost you a lot more time than doing these proto-fixes with a little bit more thought and care.

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