Fix a Non-working Electronic Fly Swatter

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Introduction: Fix a Non-working Electronic Fly Swatter

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first to…

A friend brought me her new electronic fly swatter she bought in another city. It never worked and taking it back would be too difficult. In addition, her swatter was modelled after a tennis racket. It was not the exact unit shown here. She and her husband really enjoy tennis. So, it was important to make the swatter work for her.

Step 1: Open the Case and Examine the Circuit Board

This is the circuit board from the unit shown in the introductory frame. My friend's circuit board was similar, but not identical.

Beginning from the right side and moving to the left, you see the battery leads from the switches and the red "on" LED. One of the resistors limits the current to the LED. The other provides the correct bias current to the transistor (the black object at the lower right corner of the circuit board). Transformers cannot work with direct current. The transistor switches on and off rapidly to create a rising and falling voltage for the transformer to step up. Next comes the transformer. My friend's unit has only one capacitor for storage of the charge while it builds up to the maximum charge of the capacitor. This unit has two capacitors and four diodes. I did not check it out thoroughly, but I believe the diodes and the capacitors make a voltage multiplier. At the far left of the circuit board are four bleeder resistors to dissipate the charge on the capacitors when one is finished using the swatter. The bare wires are the high voltage wires to the grid wires in the yellow swatter frame.

Step 2: What I Found

The photo shows the transistor. When I opened my friend's swatter, the smooth flat front of the transistor was largely blown away and looked like a miniature bomb crater. That was a good clue for identifying the problem.

Sometimes you can check a transistor while it is in the circuit by using the diode check function on your meter. You are looking for current to flow in one direction between two legs, but not in the other. My friend's transistor blocked all current in both directions. That was further confirmation the transistor was defective.

While this one has numbers on the face that can help to identify a replacement, there were none on my friend's transistor. NPN transistors are more common than PNP. I guessed these circuits use a low voltage NPN switching transistor, like a 2N2222. These are very common and available at Radio Shack on a blister pack.

Step 3: Replace the Transistor

I did not wick the old solder away from the holes in the circuit board, but melted the old solder with a small wattage soldering iron from below while pushing the leads into the holes from above.

Always use a heat sink when soldering the leads of semiconductors, like transistors. They can easily be ruined by too much heat.

When I finished soldering the transistor leads, I made sure the solder joints looked good. Then I put the circuit board back into the swatter frame and closed it up. (On the one shown here, the battery leads broke and had to be soldered back in place at the battery holder and one of the switches.) When I put the batteries in and pressed the switches, I rested a screwdriver on one of the grid wires and moved it near to the next grid wire. A large spark leaped from the next grid wire to the tip of screwdriver.

The transistor is the most likely component to fail in a circuit like this. Also check any diodes. I believe my friend's new swatter failed when tested at the factory. A high voltage wire was too close to part of the low voltage circuit. High voltage probably flowed back to the transistor and blew it to pieces.

Update: (September 15, 2009) The fly swatter shown in these pictures became weak in its output and then stopped working altogether. The transistor seemed to test good, but when I replaced it the LED lit again. Still, there was no spark when resting a screwdriver on one grid wire and moving it toward the next grid wire. I checked the capacitors and diodes. All seem to be good. I took ohmmeter readings on the transformer windings. The secondary read 268 ohms, but the secondary windings on an identical working unit showed 423 ohms. I am suspicious the secondary winding of the transformer has a short between its windings. Findings a replacement transformer at a reasonable price is not likely. I will probably buy a replacement fly swatter.

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    64 Comments

    0
    Shrandal
    Shrandal

    4 weeks ago on Step 3

    I replaced the regular batteries with 18650s and now it explodes wasps and or any other bug I tried 12 V and now it’s fried

    0
    Phil B
    Phil B

    Reply 4 weeks ago

    My guess would be that you blew the transistor.

    0
    Shrandal
    Shrandal

    Reply 4 weeks ago

    Yes I most definitely did I also fried at least one of the Resistors and it also melted the switch wires Post a picture when I get home Also I'm very impressedbut I had a response On a 7 year old post thank you also the circuits in the Harbor freight ones are not nearly as well put together

    0
    Phil B
    Phil B

    Reply 4 weeks ago

    If there is that much damage, the transformer may have open windings or shorted windings. The cost of repair will soon exceed the value of the fly swatter’s replacement costs.

    A safer way to boost the power of an electronic fly swatter would be to learn about voltage multiplier circuits and add a stage or two to that circuitry in the fly swatter. Those can also get into some lethal voltages and lots of caution would be needed. Most voltage multiplier circuits will include a bleeder resistor to remove the charge in a number of minutes so there are no accidents.

    0
    Shrandal
    Shrandal

    Reply 4 weeks ago

    They are only 2.99 at harbor freight tools have a few of them just messing around with them for fun.

    0
    kishort
    kishort

    6 years ago

    sir if anyone get in touch with secondary side of this circuit, can it cause of high electric shock which can lead to fatality accident???

    0
    jerrymonkey123
    jerrymonkey123

    Reply 6 years ago

    actually it is powered by two aa batteries.the current is very small and even the voltage is steped high,the amp will be low and amp is the most danger thing.

    0
    Phil B
    Phil B

    Reply 6 years ago

    I have accidentally received a shock from the secondary side of this circuit. I did not enjoy it and plan to avoid it in the future. But, it was not enough to be fatal.

    0
    kishort
    kishort

    Reply 6 years ago

    thank you sir for good advice!

    0
    MinuS5
    MinuS5

    6 years ago

    fly swatter is working perfectly but it produces noise sometime even if there is no mosquito

    0
    Phil B
    Phil B

    Reply 6 years ago

    A snapping, sparking noise? You might operate it in the dark to see if you can determine where it sparks.

    0
    arockia jegadees
    arockia jegadees

    6 years ago

    My bat was working condition.but it not get mosquito dead sound and not get dead blink light.

    0
    Phil B
    Phil B

    Reply 6 years ago

    You could have any one of several problems from weak or dead batteries to a broken wire connection to a defective transformer or a failed transistor. If you have the ability, or a friend who does, methodically check the circuit from beginning to end. Otherwise, these bug killers are not expensive and you may simply need to buy a new one.

    0
    Chetan KumarS
    Chetan KumarS

    Reply 6 years ago

    HI Phil, Can i use this mosquito circuit output as input to glow 1w LEDs connected in series/parallel.

    0
    Phil B
    Phil B

    Reply 6 years ago

    I really do not know. I doubt it.

    0
    ImdadH
    ImdadH

    6 years ago

    Thanks

    0
    Phil B
    Phil B

    Reply 6 years ago

    Thank you for looking and for your comment.

    0
    DuartmaN
    DuartmaN

    7 years ago on Introduction

    Hoe can I construct a transformer like that?

    0
    Phil B
    Phil B

    Reply 7 years ago on Introduction

    As someone commented, many of these components are in the flash circuit of disposable cameras. It seems, though, you could get the same effect with two transformers and a diode. Connect the second transformer's secondary to the output of the first transformer. Connect a diode to the primary of the second transformer for the low voltage current to switch the transistor on and off. The second transformer could be a lighter duty, lower wattage transformer.

    0
    DuartmaN
    DuartmaN

    Reply 7 years ago

    thanks, I will try it :)