Picture of Fully Functional Television Oscilloscope
There are a few Instructables and otherwise internet based instructions on how to modify a television set into an audio visualizer or other simple oscilloscope-like device. This Instructable will show you how to create an actual lab oscilloscope worthy of a poor, amateur electronics enthusiast. The final product has optional audio output, variable input voltage from millivolts to hundreds of volts, as well as manual horizontal frequency locking. The total cost for this project was around $20.

To give proper credit, this Instructable is an improvement on Magnelectrostatic's at http://www.instructables.com/id/How-To-Make-A-CRT-TV-Into-an-Oscilloscope/. I wouldn't have been able to complete my mod without it. Thanks!

UPDATE (12-28-10):
This mod is not capable of displaying much outside the human audible range (20-20k Hz).

Also, since TVs are highly variable in design, this Instructable is intended for people who can do their own experimenting. This of course requires experience in electronics. Your TV will probably be different from mine. My instructions may not apply to what you're working with. They're guidelines. I hope they help you modify your available resources by providing ONE particular example.

Step 1: Safety

Picture of Safety
This project involves working in close proximity to the television's exposed flyback transformer and high voltage capacitors, which are both potentially lethal devices if you do not take proper safety precautions.

First, the obvious step: Is it plugged in? Unplug it! Isn't it funny that this is the exact opposite of what a tech normally tells you...

When you remove the shroud, be careful not to rip any wires from the circuit board, and do not touch any of the exposed contacts. Identify large capacitors and take note of their voltage ratings. 50v and above are especially dangerous, and should be discharged with a well insulated screwdriver across the contacts prior to tinkering if possible.

UPDATE (12-28-10):
Ok, ok, I generally dislike disclaimers because they are almost never legally sound. But for those of you who don't get the idea from the above paragraphs...

Don't attempt this unless:
you have a solid grasp of high voltage safety practices.
you have a solid grasp of electronic equipment in general.
you have someone around to call 911 or give you CPR.
you have experience working with mains (120VAC) power.
you are not a moron.

I take no responsibility for damage to your health or equipment. All damages incurred are the sole responsibility of the end user.
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JohannaL2 months ago

do you by any chance have a eagle file or pcb lasyout?

Hi hoping someone with some knowledge can help me out. Im using 2 of these in a performance and have one working perfectly in lissajous/xy mode. This tv is a really old black and white one like the one used here. The other is really old as well but is a colour tv. I had an amp connected to the horizontal coil and it was working fine. I then connected the other side of the amp to the vertical as well for x/y and once i switched on the power... bye bye amp. It fried it.
So i have another amp and everything else is working but i havent tried the vertical coil again. I measured the 2 wires coming from the vertical with a multimeter and im getting a reading of almost 60 Ohms. All other coils on both tvs are nowhere near this level of resistance but my electronics knowledge is very small so im not sure what this means. Can someone shed some light and tell me if it's still possible to use this coil with an amp?


So wonderful! I'll add a link to our "Music You can See" 'ible. This is incredibly awesome

jgodalla7 months ago

Very nice and clear instructions - thank you. I have modified a TV as per the instructions, and have a nice blue horizontal line now being driven by the vertical output of the main board (horizontal output is disconnected and sealed off for safety). The leads to the vertical deflection coil now terminate at two binding posts on the front of the TV to accept inputs from various devices. However my blue horizontal line occupies just the centre half of the screen leaving about 75mm blank either side. It seems to work OK, because a 9v battery across the binding posts shifts the line to [almost] the top of the screen, and ac inputs appears as sine (-ish) lines, but can anyone tell me what to tweak to spread the line fully across the screen?

laserjocky (author)  jgodalla5 months ago

I had this problem too. If your TV has ring tabs on the back of the tube, the long cylindrical glass part, then rotating those rings might help a little. I think that's what worked for me.

Did you say it's capable of 20 KHz? Or 20 Hz? Or both? I was confused
laserjocky (author)  Engineeringmaster1069 months ago

Both. The signal is hard to see at those extremes, but I could see 20kHz in my version.

Cubytus1 year ago

I tried to build it, but for some reason the sound from the loudspeaker is really weak, and the horizontal line barely moves. Any idea?

laserjocky (author)  Cubytus1 year ago

This circuit should be able to push plenty of current into a speaker. It's possible the coils in your TV are lower impedance than mine and are using more power. Try disconnecting the circuit output from the coils and have it go only to the speaker. Does that make the speaker louder? If so, you'll need a more powerful circuit. If that doesn't help, check your resistor values to make sure you're getting the amplification you want.

Nikola0101 year ago

I have one question, how horizontal beam works? Does controller linearly increases voltage from 0V to i don't know how much or? If so, how much is that voltage and if i make circuit that can make refresh rate more than 60Hz, and control it refresh rate, can i make it work on much higher frequencies? Of course i know how much restriction inductor make, but in theory if we forget about that coils on sec.

laserjocky (author)  Nikola0101 year ago

Someone asked me this a long time ago and I think we finally decided that making the modification you describe is a lot of trouble, probably more than it's worth. You could, in theory, make a controller to sweep the e-beam horizontally much faster than 60Hz. Really that's what the flyback transformer does. You end up needing huge voltages to sweep at rates of thousands of Hz because of the inductance of the coils.

Cubytus1 year ago

Maybe my question is silly, but in lieu of the TL082, would it be possible to use a pair of LM741? Does it make any difference in this application?

laserjocky (author)  Cubytus1 year ago

Sorry for the slow reply. For this application it probably doesn't matter, since the signal quality is going to be heavily distorted by the TV magnetic coils. You can use a 741 here. If you needed higher quality signals then the TL08x series is better than the 741. TL08x has higher slew rate and higher input impedance. In short it's a more ideal op-amp. I used the TL082 because it was at Radio Shack and it contains two op-amps.

double_g1 year ago

I have a perfectly good oscilloscope on the desk behind me, but I still want one of these haha. Pretty neat project!

laserjocky (author)  double_g1 year ago

Thanks! When I made it I had no access to oscilloscopes and this was supposed to be the solution to that. It's not the most accurate thing in the world but it did the job. Now I work in an electronic materials lab and I am surrounded by them. Go figure.

Well I have just successfully made the first part of the build. I used a 2004 Sharp color TV that was laying around. Everything was successful for the most part. I have the same problem many others have with the slightly short horizontal line, but the line does oscillate with the music. My main question is whether or not it is feasible to hook up the speaker in the tv for music playback.

color tv works even if it dosen't have the horizontal scanning pot
OMG, that is awesome! I'm making one!
robot7972 years ago
can anybody tell me how to trick the tv into working
without conection the horizontal deflection coils
i have a tv and it does not funktion without them
and i need an x and y
T_T_ robot7972 years ago
try putting a resistor in place of the coil, probably 5-10 ohms, or you could measure the resistance of the old H-coil, then find a resistance close to that
Sun Gear2 years ago
If you had 2 inputs, one going to the V-coil and the other to the H-coil, would that be able to make a vectorscope?
T_T_ Sun Gear2 years ago
yes, but remember that each coil takes a different amount of voltage to go the same distance
T_T_2 years ago
Is there any way to make a square wave appear as a square?
Is there any circuit that might be able to do that?
jackscrap2 years ago
i have a similar problem, and an extra coil, please explain how yo proceeded, Jerkey.
musick_082 years ago
I want to make one of these for high voltage systems (around 220 vac), if I were to use a portable TV, would I follow these steps, or would there be other changes I would have to make since they operate off of 12 vdc?
jackscrap2 years ago
i am attempting this ion a computer monitor, it has a for cables labeled vhot, vcold, hhot hcold switched them, as you suggested, but all i get is a horizontal bar that moves up and down, also it fries anything connected to it I've pulled tvs apart before so i'm sure they are the right cables, i'm running out of media devices to try, can you offer any help? by the way i searched for quite a while this is the best Oscilloscope tutorial I've been able to find thanks
stealthop2 years ago
i have tried to do this twice now , both times the tv caught fire. it really stinks too. so my tip would be keep a fire extinguisher nearby and do this outside . proceed with caution!! ;)
laserjocky (author)  stealthop2 years ago
Yikes! Someone who knows CPR would be good too. Any ideas as to the why of fry?
I opened up a small tv and connected an audio source to it, but the display only shows a horizontal bar that "fattens" with the music. It does not show waveforms. What did I do wrong?
laserjocky (author)  cardboarddude3 years ago
That's strange. This is after you put the vertical scan wires on the horizontal coil, right? The high frequency horizontal scan is so fast that you wouldn't be able to see the waveforms. That's why they are replaced. If that's not the issue, then it may be that the TV doesn't support this mod.

The audio source physically deflects an electron beam in this mod. If the deflection coils are complex or have other circuitry attached to them, this might not work. I've tried this with computer monitors before and I ended up with a oscillating thick line. I couldn't figure out how to make it work.
Yes, I'm pretty sure I replaced the wires correctly, and now i just have a thick oscillating horizontal bar like you said.

So is there no hope for this tv set!?
laserjocky (author)  cardboarddude3 years ago
Probably not. When was it made? Newer models probably have fancy correction circuitry that messes up the basis for this mod. My TV was an Emerson 1987 black and white model.
jungkurth4 years ago
I made one of these from a Popular Electronics article in the late 70's - and used a color set. Made a simple bandpass filter, and had the low-midrange-highs split out to the three colors, which was amazing. Brought a whole new world to "watching" Pink Floyd Animals...Pigs on the Wing? Dogs? Unreal!
How did you split it into three colors? I have one of these I made from a B&W TV but happen to have a 10" old color TV I had planned on experimenting with.
Sorry for the delay, have been offline for a bit. Easy to do, harder to explain, but tbasically, the three dots in a color set are controlled by three sets of 2 wires - and you have accesss to drive the audio output through them to control the voltage that then moves the h and v dots - into lines - into lissajou patterns.
I would hug you right now for the choice of music! 8D
jhoeffer3 years ago
I had the same problem with it not taking up the whole screen so I switched the h coil and v coil inputs then i rotated the coils so that the line was horizontal again. Worked like a charm and now my line is rainbow colored. :)
zapro3 years ago
Sorry to muck around, but the wires for the Horizontal deflection does NOT carry 15.000 volts.

The Vertical coil is usually driven at about 80-130 volts peak.

You should be aware, that the Horizontal coil is wired in parallel with the flyback transformer, and the high voltage will change when removing the coil from the circuit, raising or lowering the high voltage (usually the latter)

The highest voltage you'll find in a TV set is the EHT Flyback connected to the picture tube via the thick cable in a suction cup looking thingy. On a B/W set you'll have approximatelt 10 Kv (Kilovolt) on this, and on a Color monitor Approx. 25 Kv.

I have done this mod a couple of times, and have replaced the Horizontal coil with an other inductor to keep the circuit working correctly. Around 400 uH of inductance should do it.

I added a Schematic cutout showing the Horizontal coil connected across the Flyback.
Screen Shot 2011-09-20 at 00.12.08.png
laserjocky (author)  zapro3 years ago
Whoops, sorry for the late reply. Thanks for enlightening me on this zapro. I vaguely remember trying to measure the voltages of the coils when I was working on this and my voltmeter didn't particularly like it (the display went all wacky). It may have been the high frequency but my guess at the time was very high voltage.
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