DIY Analog Oscilloscope From Old TV

Oscilloscopes are useful for troubleshooting electronics. But when my oscilloscope broke recently i decided to take the DIY approach to replacing it. Unlike modern TVs, old CRT TVs have 4 wires that control all the motion on the screen. By inputting a signal into these wires you can use the TV as an oscilloscope and see the signal on the screen!

Supplies

Old CRT(Tube) TV

soldering iron

solder

Audio amplifier(i just removed one speaker from my dad's stereo system and used the wires connecting the two speakers as the output.)

16 gauge insulated wire

wire cutters and strippers

screwdriver

multimeter

Step 1: Disassemble the TV

This is pretty easy. Just take out the screws from the case and pull the back off. The back of the TV has a weird locking mechanism so be sure to pull it out carefully to avoid breaking the circuit board in half, which ruined my first attempt at doing this project. once the back is off DO NOT TOUCH ANY PART OF THE TV!!!!! The big tube can hold 5,000-30,000 volts of charge even when the TV is unplugged. clip a jumper wire onto something grounded and clip the other end onto a screwdriver. Be sure that you are holding only the insulated part of the screwdriver and not touching the metal part and then carefully slide the end of the screwdriver under the suction cup that is stuck onto the tube. you might hear some pops and crackles from it discharging.

Step 2: Find and Disconnect the Deflection Coil Inputs

Now look for the large coil of wire that is wrapped around the tube. there are four wires connected to it. these wires go to the two separate coils wound together to form one coil. First disconnect them from the circuit board and use a multimeter to test which sets of wires have continuity to each other. tape together the sets of wires so you know which ones go together. now reconnect one of the sets to its place on the circuit board but leave the other set disconnected. now turn the TV on. there should be a line across the screen. if the line is horizontal then the wires connected to the board go to the vertical coil. if the line is horizontal than the wires go to the horizontal coil. now disconnect all the wires and connect the vertical coil wires to an audio cable.

now connect the wires from the horizontal coil to the vertical coil wires from the circuit board.

Step 3: Connect the Audio Amplifier

Now you need to connect the output of some kind of audio amplifier to the audio cable. You can use a cheap 420w amplifier board from eBay or do what i did and tap into the wires connecting the two speakers in my dad's stereo system because it has a built in amplifier. the audio input of the amplifier is your oscilloscope input. Be sure to not input more than 1v into it.

Step 4: Test Your Oscilloscope!

Now connect your computer's headphone jack to the amplifier input, play a song(i suggest skrillex) on it, turn on the TV and you should see the waveform of the music on the screen. If it doesn't work leave a comment and I will reply with troubleshooting help ASAP. Once you get it working, you can use a 10-1 or 100-1 oscilloscope probe to lower the voltage of the input, allowing you to troubleshoot electronics projects with this oscilloscope.

Step 5: Enjoy Your Oscilloscope!