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Fully Functional Television Oscilloscope

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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.
 
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Step 1: 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.
double_g1 month 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 month 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.

Slashmaster2 months ago

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.

NeoRecasata6 months ago
color tv works even if it dosen't have the horizontal scanning pot
CoronaAndOzone10 months ago
OMG, that is awesome! I'm making one!
robot7971 year 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_ robot79711 months 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
vernors11 months 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_ vernors11 months ago
yes, but remember that each coil takes a different amount of voltage to go the same distance
T_T_11 months 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?
jackscrap11 months ago
i have a similar problem, and an extra coil, please explain how yo proceeded, Jerkey.
musick_081 year 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?
jackscrap1 year 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
stealthop1 year 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)  stealthop1 year 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)  cardboarddude1 year 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)  cardboarddude1 year 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.
jungkurth3 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
Brofist!
jhoeffer1 year 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. :)
zapro2 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)  zapro2 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.
Djdavies832 years ago
Hi Andybiker and Aeternusjunk, I've been wanting to try and locate the data in pin on a Syma S022 Chinook Tx and the output pin on the Rx as the chips not labled , I need an oscilloscope for this so I did some searching and this is the best that I have found good job!


now the questions for you both, I have a 5.5" black and white plustron TV/FM radio that runs on 12V, Same kinda thing as used here, single channel that needs to be tuned each time.

The wires from the board to the coils are labled H1/H2 and V1/V2, that saves a bit of work but now I am wondering about the amp ciruit, is there anyway to make it run on 12V, it would be really nice to have the whole thing on 12V to save on transformers and also run it from a battery if needed.

I will of course be doing model specific instructable, Aeternusjunk, would you mind if I used this build as a foundatio, use the odd paragraph here and there?

Great work dude!
laserjocky (author)  Djdavies832 years ago
And I suppose *technically* you don't need the voltage regulator either.
laserjocky (author)  Djdavies832 years ago
Hi Djdavies, and thanks! You may use information from my instructable as long as you say that it came from this one and you don't make money off of it. I think that's the basic summary of the license it's under.

The main problem with a 12v power supply is the op-amp used in the amp circuit. Everything else will be fine, but the TL082 requires a minimum of +/-7v to operate properly. This means you'd need at least a 14v battery to run the amp. So close, yet so far. It might still work, so test it! However, there are low voltage op-amps such as this one that would be a good replacement. Basically you are looking for a 2 channel, through hole, dip-8, +/-6v supply (or lower) op-amp. Anything that fits that description should work. If you're running things from a battery, just chop off the AC rectifier section and you're gold. This is everything before and including the 4 diodes, but I recommend keeping the filter capacitor.
jgfresh2 years ago
dude u should hav made a new housing :)
laserjocky (author)  jgfresh2 years ago
I know right?? It would have looked a lot better. Oh well, as long as it works I'm happy.
yeah
234BUG2 years ago
Could the ociloscope measure 220v?
laserjocky (author)  234BUG2 years ago
Sure. The circuit is theoretically capable of attenuating the input to 1/1000000. But please be careful when playing with your mains power. AND, the amp has no protection to prevent destroying the circuit if you accidentally have it set on a more sensitive setting. The thing that allows you to hook up large voltages is a 10MegaOhm resistor on the rotary switch. If that one isn't selected, get ready for some sparks.
magnet183 years ago
Would it work to find what drives the 30kHz horizontal signal and wire it into a signal divider circuit?
Wouldn't this let you choose the frequency, giving a lot more flexibility and make it more useful?
Or is that just so complicated that it isn't worth it?
the 30Khz signal is amplified not only to make the horizontal line, it also is used to generate the 16KV+ for the picture tube. changing the frequency will change the voltage to the tube and probably blow the driving transistor.
laserjocky (author)  magnet183 years ago
You could certainly try that, but I'm guessing that circuit occurs before the flyback transformer, since the flyback drives the high voltage, high frequency horizontal sweep. You'd most likely need an oscilloscope to determine which area to modify, and that is just paradoxical. Another option may be to replace the trimpot that controls the desired frequency with various resistor values to see if the control circuit can be modified easily that way. I haven't tried this, but it's worth a shot if you're looking for increased time resolution. Just remember that the fundamental reason for the high voltage signal is to overcome the impedance (frequency dependent resistance) of the deflection coils. If you want high time resolution, you will need to modify the circuit somewhere before the flyback.

The other problem, as I'm now realizing (or re-realizing) is that any signal of high enough frequency to warrant preserving the high horizontal scanning frequency will itself be very high frequency, subject to the impedance of the vertical deflection coil. You would need a another independent flyback transformer just for your input signal. This sounds like a lot of work to me.
Thanks, good thing I have plenty of flybacks lying around :)
I think I'm going to need to severely modify some things, considering the ancient monitor I want to use dosen't have a full image displayed.

Ill let you know what happens.
Gas Mark 53 years ago
Thank you for this brilliant instructable. I have identified and removed the wires connecting the horizontal deflection coil, and get a nice pretty vertical line on my screen. However, when I solder the vertical deflection coil in place of the horizontal, I still get a vertical line on my screen, only this time the line is only about 5cm long, whereas before it ran the entire length of the screen. I've tried reversing the polarity, to no effect. Does anyone have any suggestions?
If it makes a difference, it's a 5.5 inch b/w portable tv...

Thanks!
just reconnect them to where they were and loosen the screw of the defection coil assembly. rotate it 90 degries and fasten the screw again. use the now horizontal coil for your audio signal.
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