Step 15: General troubleshooting

• Make sure the interrupter works (refer to Step 2).
• Make sure your coil passes Step 6, “Low Power Testing”.
• Make sure the fuse is installed.
• Make sure the stack of standoffs that connect the driver board to the resonator board is securely installed, including the screws on the resonator board.
• Make sure the 78L05 and 78L15 are not switched.
• Make sure C4 and R4 are installed and properly soldered.
• Make sure the IGBTs are soldered in properly.

A dead bridge is a dead short

If you attempt to re-test your coil right after a severe failure by simply putting in a new fuse and trying again, you’re likely to just blow the new fuse as well. A damaged bridge acts as a dead short and will blow fuses instantly, possibly also tripping a circuit breaker upstream. Check your IGBTs if you’re in doubt!

If the fuse blows immediately upon plugging in the coil, you have a severe solder bridge, a backwards rectifier D4, a backwards bus capacitor C11 or C12, or improperly isolated IGBTs. Unplug your coil immediately and inspect your driver for issues.

If immediately after the fuse blows you look at the output of the interrupter and see a solid red light that doesn’t turn off, your interrupter has latched up high, outputting a 100% duty cycle and overloading your coil. This is caused by the microcontroller crashing, which is typically due to being too close to the coil with your interrupter and picking up noise. It can also be caused by a low battery level.

Other causes of failure during operation include running the coil at high power for too long, drawing too much current from the coil by pulling an arc with a metal object, or running at high power in a non-optimal environment that de-tuned the coil.

• Make sure you and the interrupter are the full length of the fiber cable away from the coil.
• Switching IC1 and IC2 is known to cause this problem.
• Make sure the coil is properly grounded.
• Make sure the batteries in the interrupter are fresh.
• Double-check your interrupter’s soldering. Bad joints will sometimes pick up noise from the coil.

Turning up the power when the spark doesn’t sound clean or is performing weakly will not make the problem go away! It’s better to not increase the power, but try to track down the problem.

How to check your IGBTs

Use a multimeter to check that your IGBTs behave like a diode between pins 2 and 3. On a resistance measurement setting, the pins should read open in one direction and a near short in the other direction. Some multimeters have a diode test feature which shows you the diode voltage drop, which is a better test. A complete open or short in both directions indicates dead IGBTs.

Your driver is working (hooray!) but there is internal flashover inside the secondary. You can confirm this is the case by watching your Tesla coil in a dark room and observing a glow from the acrylic cap on the bottom of the secondary, indicating the spark is on the inside. Check for dangling wires or bits of glue or other stray debris inside the tube. Use a flat-tip screwdriver to pry off the endcap. If you see burned tracks inside the secondary, use a file to remove them and drip some varnish over the area.

• Add more varnish to the secondary.
• Check your grounding.