How To: Make a CRT TV Into an Oscilloscope

Introduction: How To: Make a CRT TV Into an Oscilloscope

About: An electrical engineer who likes to make things.

This is the simplest possible way to make a CRT (cathode ray tube) TV into an oscilloscope, it can be done in about half an hour.

Supplies
-A CRT TV (color may work, but I'm not sure)
-Some wire
-A soldering gun
-Rubber gripped pliers (for safety)
-A screw driver

Step 1: Identify Wires

After undoing all screws remove the cover from the TV.
Inside wrapped around the CRT are two coils of wire, one controls the vertical deflection of electrons, the other controls the horizontal deflection.
Find where these coils of wire attach to the circuit board, and desolder one coil.
Place the cover back on the TV(for safety) and plug in and turn on the TV.
If you see a horizontal line, you desoldered the vertical deflection coil.
If you see a vertical line, you desoldered the horizontal deflection coil.

Step 2: Placing Wires

Desolder the vertical coil if you haven't already and attach extra wire to the vertical coil, this will have to be long enough to come out of the TV so you can attach a voltage source.
Now desolder the horizontal coil, and solder it to where the vertical coil was.

Step 3: That's It

Really, it's an oscilloscope now.

Step 4: How to Use It With Music

I use mine to watch the waves created by music from my mp3 player
First take an old pair of headphones and cut one off, then strip away some of the insulation.
Now you should have multiple exposed wires, one will be slightly thicker than the others and wll have a thin coating of insulation on it - scrape it off.
Attach this wire to one end of the vertical coil, and the small group of wires to the other end.
Now plug it into a sound source, remember your attaching your mp3 player (or whatever) to a giant coil of wire, and there's chance it could break.

6 People Made This Project!

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131 Discussions

Hi ..?
This is the third TV burnt !! ?
It was showing that line and then after 7 minutes suddenly disappear! it is happening every time
Why that does not work with me?
The TV is working but the screen is black.
The horizontal coil supposed to handle the 60hz what is the wrong ?
I even could not try that circuit you suggested ...

5 replies

Sorry I took so long to respond! And I'm sorry about all the TVs; that's too bad.

The TVs don't work at all any more? And does anything actually burn? Do any components inside look like they failed?

Moving the deflection coils shouldn't make anything change in a way that would break the TV

no problem
actually I finally did it! and I find out what was the problem
thank you very much for your help :) and your instructions.

Hello! I think I got the same problem as you at the time.

I can't get no line or point... The Tv is on, but the screen stays black. On the front panel the led blinks, wich is not habitual...

Do you have any idea? Is my Tv not old enough? I tried on 3 different TVs and only on of them works just fine (apparently the oldest one).

Thanks!

Tim

Try connecting a "dummy" coil to the disconnected output. Try to choose a coil of similar impedance to the yoke. (1-2mH, 5-10 ohms).

Next time try using a small black and white unit. The simpler the better.

This is so cool, I found this old tv years when clearing out a storage room for my old employer. I'm gonna try to do this, but I'm very new at soldering, so I think I might try another project first. This one has a jack input behind for receiving signals. Maybe I could reroute it for the oscilloscope input?

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8runo

1 year ago

I nailed it second try. Really easy and fun nice instructable

hi! I've already done this with an old crt tv but I was wondering if it would be ok to connect the tv's own audio wiring to the coils so I can just input an audio signal (somewhere in the circuit) and use the tv's own amp to drive the coils, I haven't done it yet because I think it might be dangerous but what do you think?

2 replies

I like the idea! If you find the speaker(s), it should lead you right to the TV's amplifier, and if it's an integrated circuit (a chip) you might be able to look it up online for more info.

There's always danger working inside the TV because of the high voltages. As for this specific modification, the amplifier is not designed to drive the deflection coils. This could potentially lead to excessive heating which, in the worst, case means fire! I don't think that's particularly likely, but if you try it, be safe!

Thanks! Yeah in fact I was able to input my own audio into the tv amp and hear ir through the speaker. So I'm gonna proceed now... I'll be posting images soon

I am not surprised people are killing TV's. It is not uncommon for Large, color displays to have protection circuitry that shuts the system down in the event of a deflection coil failiure. When these things were new they were very costly and vulnerable to permanent damage from burn-in. Any one this worked well for no doubt noticed how intense the trace is at normal brightness. Normally that beam scans the whole frame. My advice is to find yourself a small black and white crt to work with. Early Macintosh computers (SE, Plus, SE/30, etc) are excellent for this. Very rugged.

As for the input, direct feeding the vertical yoke is awfully crude. In order for this to behave anything like a real scope from the signal's point of view, you need a buffer, an amplifier, and an impedance matching network. Otherwise referred to as the scope's vertical amplifier. If you don't know what that means or how to put that sort of thing together, if the TV you're working with has an audio input, I would recommend finding the wires leading to the TV's speaker, sending them to the vertical yoke, and putting your signal through the audio input. If you're using a monitor or sound is no good, you could also use any old stereo power amp that can drive low impedance speakers.

Hi
I do all the instruction for 3 tv !!!

One of them dosnt work anymore
and the rest show that the herizontal line but when I contacted to the signal sources still show me that line

There is no wave shape. :(

7 replies

What type of signal source did you use? It's possible that it wasn't strong enough. A good source to test with is a battery connected to a potentiometer. You can put the center pin of the potentiometer on one end of the vertical coil and ground the other, then you should be able to move the line up and down.

First I want to thank you

I am sorry if I am gonna bothering you
I want asking you
I don't think I get it !

I connected with my laptop and then my phone and I played some video on YouTube that had 20~3000 Hz
Is not enough ???

And you are suggest that I should to connect the v-coil with battery and potentometer just like that without a laptop ???


Not a bother at all! Your laptop or phone should work fine, was the volume turned up high?

And yes, no laptop. I've attached a crude image of the setup.

Test circuit.png

Hi...
It is me agin :)

It is ok if I choose a 9 volt battery ?
And what would you suggest for the pot ?
1 kohm good ?

Both of those should work, but you might want an additional resistor of 100 to 1000 ohms in series with the battery to limit its current. You can also just limit it by how far you turn the pot.

Now, this reply is getting a bit longer than I had hoped...but I think on my TV the vertical range was only about a volt, if even that, so I imagine a AA (or AAA or D) battery would also work fine, and with the 9V battery you might only have a small range on the pot that's visible on the screen. If the voltage goes too high or too low (negative) the line will disappear completely!

I'm also not sure what the resistance is in the coils (if you have an ohmmeter you can always measure it!) and I'm not sure how much current they can handle, which is why I recommended the additional resistor - to prevent the battery's full voltage from falling directly across the coil.