Questions tagged [crt]

Anything related to Cathodic Ray Tubes (CRTs), i.e. specially built electronic vacuum tubes where an electron beam is focused and deflected on a phosphor-coated surface in order to display an image.

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Why don't most electrons hit the anode in a cathode ray tube or electron gun?

In a cathode ray tube or electron gun, electrons liberated from the cathode by thermal emission accelerate towards a ring-shaped anode, from the potential difference between cathode and anode. If an ...
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1 answer
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Effects of too-frequent serrations in vertical sync pulse on analog horizontal deflection oscillator

Normal analog TV video signal has a vertical sync pulse with serrations to help keeping the horizontal oscillations in sync. Also, as I understand it, in case of an interlaced video, these serrations ...
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2 answers
70 views

An overview of the inside circuit of a CRT [closed]

I want to know how the inside circuit of a CRT looks, from what I've understood it is that you heat the cathode, then some of the cathode electrons are released, then it gets focused and accelerated ...
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4 votes
1 answer
522 views

Is it possible to use CRT tubes for audio amplification?

I was wondering if it's possible for me to use the tubes in an old CRT TV to build an audio amp (specifically a guitar amp). If not, would I be able to salvage something else (like an old radio) to ...
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0 votes
1 answer
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Thermionic cathode heater filament conundrum

An old CRT I have specifies 6.3 V (DC, I believe) on the heater filament, resulting in a 0.6 A filament current (spec). But I measure the filament resistance as 1.8 Ohm. At V = 6.3 V that would result ...
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Questions about deflection coil interlock on CRT TVs to restore beam brightness control

Electronics noob here, with experience in science and research. I am trying to make a music visulaiser out of an old monochrome CRT TV by connecting the horizontal and vertical deflection coils to an ...
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0 votes
2 answers
106 views

Fixing composite video distortion caused by brightness changes

I'm modifying an old CRT to take NTSC composite input (it only accepts RF over coax.) I have got a good signal going in but it has this weird distortion going on. When the image is dark the pixels may ...
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1 vote
2 answers
146 views

Mystery Monochrome Monitor

I rescued an old monochrome monitor from the e-waste, but the cord had already been cut. So now I’m trying to see if I can get it working. I know… This is of an era that rather than have a connectors ...
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1 vote
2 answers
90 views

Components of a CRT whine

I noticed something as a kid with my Atari 2600 (and better ears). We can hear the 15khz horizontal freq but I noticed that the whine changes slightly (while the line frequency doesn’t) based on the ...
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-2 votes
1 answer
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Digital to analog in an old 35mm film recorder [closed]

I'm looking at an old film recorder from 1985, the Polaroid Freeze Frame, the back of the machine pictured here: From here: https://www.radiomuseum.org/r/polaroidco_freezeframe_video_recorder.html I ...
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4 votes
0 answers
164 views

How to understand a complex diode-resistor function generator circuit?

I'm reverse-engineering a CRT anti-pincushion circuit and it uses a complex diode-resistor circuit to approximate the function X-k×X×Y², where X and Y are the deflection voltages. My question is if ...
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2 votes
0 answers
51 views

Why does changing CRT to HDTV lose antenna channels? [closed]

We have an internal antenna that is connected to a tiny CRT TV through a digital converter box. I recently replaced this CRT TV with an HDTV, and I removed the digital converter box since the HDTV ...
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0 votes
2 answers
55 views

Will discharging work if the grounding chassis isn't connected to the mains or otherwise grounded?

Suppose you have a CRT screen and you want to dismantle it for whatever reason. The high-voltage anode needs to be grounded in order to avoid the risk of electrocution. The metal grounding chassis of ...
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0 votes
1 answer
133 views

Neon bulb lamp replacement for surge suppression

I'm restoring an HP 141T and it has a broken neon lamp which is used I believe as surge protection in the following configuration: On the right is the CRT. I believe the only purpose for such lamps ...
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0 votes
2 answers
118 views

Are fluorescent tubes dangerous?

I'm disassembling a Sega GameGear. The capacitors inside are all rated 50v or lower, so it shouldn't be hazardous in that regard (I will discharge them anyway just to be sure). However, the metal ...
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1 vote
0 answers
107 views

How to get static on CRT screen instead of black screen?

The TV in question is a Sony Trinitron KV-14M1D CRT. I know it sounds backwards but I need the screen to show white noise for a project (oscillograph); but there seems to be a static block that ...
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0 votes
3 answers
126 views

Old tvs, how did storing settings work, and what changed in the tv when we tuned a channel?

I don't have an EE background, but I would like to understand some aspects of old TVs. When we tuned channel what exactly changed inside the tv. Was there a circuit card in the tv where something ...
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23 votes
7 answers
5k views

How did old television screens with a light grey phosphor create the darker contrast parts of the display?

Many old television screens have a very prominent "light grey" color to the glass, I'm guessing from the phosphor, create darker areas if the effect of electrons make the phosphor glow? Is ...
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How to adjust picture geometry of a CRT TV?

I have a HD CRT TV (Silva Schneider 26 inch) which failed recently. So I took apart a working CRT TV (Philips L01-2E AA, 20 inch) and took its mainboard and connected it properly to the HD CRT tube. ...
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0 votes
4 answers
114 views

Geometric information within 1D streams of electrons/photons

How is light—or actually any frequency in the EM spectrum—self-encoding and self-modulating 3D info in its 1D self, so that it “knows,” once it strikes a surface, to discharge all the data perfectly ...
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0 votes
0 answers
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How do I safely discharge this Trinitron CRT when the HV connector seems glued on?

I'm trying to discharge a Sony PVM-1353MD which suffered shipping damage. Unfortunately, I am unable to get my tool under the HV connector. It seems bonded to the CRT with some kind of white silicone ...
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1 answer
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Are analog CRT oscilloscope becoming rare? [closed]

Back in the early 2000s I bought cheap Commodore 64 sets from eBay, we were able to get huge collections for under 100 USD. Today they are rare and commensurately expensive! Today you can get analog ...
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0 votes
4 answers
380 views

Does an isolation transformer make CRTs any safer to work with?

CRT tubes are often described in training materials as huge capacitors capable of delivering very high voltages, often enough to severely injure or cause death. Before working on them, they should be ...
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2 answers
121 views

What was the point of an "alignment scope" like Kikusui 5091, and can anything be done about it's dismal horizontal bandwidth?

I got this Kikusui 5091 used for US$ 50 bucks, as a reward for my pretty successful attempt to create a digital raster display from scratch on my oscilloscope, and finishing off my Game of Life in ...
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-4 votes
1 answer
249 views

Is safe to work with a CRT viewfinder? [closed]

While searching, I found CRTs that run at 5V-12V. These CRTs can run with very low power but is it risky to touch them? You can power these CRTs with 9V batteries but if you lick 9V batteries it ...
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0 votes
1 answer
75 views

How would I switch between either of my two outputs into one input?

I am trying to design a circuit which will switch between two RGB outputs into a CRT TV's neck board. Each of the two outputs has three pins. I have tried using the 2N3906 PNP transistor, and it works ...
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2 answers
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Why do LED/OLED HD and UHD displays have "global refresh rates"?

What is the benefit to scanning vs. individually addressing and updating lines or pixels or screen areas? Is there a standard interface to the majority of HD or UHD displays that allows the ...
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2 answers
80 views

How do I take proper voltage measurements on device with multiple voltage sources sharing the same ground?

If you recognize me, it's in reference to CRT scopes again. I don't understand how to take proper voltage readings on the circuits. An example is the heating element in the CRT. When I hook both test ...
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11 votes
2 answers
893 views

Image position and size controls vs beam alignment in a color CRT

If you look at a the shadow mask of a color CRT, you can have a pattern like this: Most TVs were purely analog and had knobs to move the picture horizontally and vertically. How does the green gun ...
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0 votes
0 answers
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Amplifier transistors not receiving change in base voltage... do I look forwards or backwards?

So I'm working on diagnosing a CRT scope that isn't responding to the horizontal controls; the trace is off screen. The two X plates are each being driven by 2 transistors in line. One X plate has ...
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6 votes
5 answers
16k views

What purpose are the transistors serving in this CRT oscilloscope circuit?

So this is part of a CRT oscilloscope diagram, and I don't understand the function of the transistors on the bottom right, Q18 and Q19. Their outputs (41 and 42, crossing through the dotted line) go ...
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3 votes
2 answers
117 views

Does the electron beam go towards the deflection plate with the higher, or the lower voltage?

So I've started tearing apart an old CRT scope to learn everything about them, and right now looking at the voltages on the deflection plates. When the trace goes down, my vertical plates read (a)193v,...
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1 vote
2 answers
292 views

How can chassis ground be used for voltage measurements in a device with components of differing voltages?

The manual for my HV probe tells me to connect my ground clip to the chassis. I can see how this would be good advice for say a 12V car, because the chassis is made the ground and every component uses ...
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8 votes
2 answers
2k views

Fixing old CRT oscilloscopes... what to look for first?

I've been amassing a pretty large collection of these old scopes, and it's about time I got to trying to fix them. About half of the ones I run across and buy don't have traces. I don't need to get ...
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0 votes
1 answer
79 views

Have CRTs ever used a different raking pattern? [closed]

CRTs traditionally scan top-left to bottom-right, in a row-major raking pattern, and appear to have done so since the 1930s. This is a little unusual though, as standard mathematical orientations have ...
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0 votes
0 answers
55 views

CRT automatic focusing?

Has anyone ever heard of a circuit to automatically adjust the focusing anode on an electrostatically deflected CRT? Is there any way to even detect optimum focus other than by looking at the tube ...
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1 vote
1 answer
84 views

What receiver is appropriate for studying compromising emanations in 2019?

I'm currently reading the Cambridge Technical Report Number 577, Compromising emanations: eavesdropping risks of computer displays, by Markus G. Kuhn and published in Dec 2003. In the paper, Kuhn uses ...
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28 votes
6 answers
5k views

Why wasn't interlaced CRT scanning done back and forth?

I was studying the scanning of old CRT screens and the interlacing strategy for video, and I started wondering something. The raster scan process went top to bottom on odd lines, then back to top to ...
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2 votes
1 answer
297 views

Why doesn’t the focusing anode diverge the electron beam again?

Consider this diagram of a focusing anode in a CRT: Question: Why does the electron beam not diverge again when it enters the focusing anode (or accelerating anode) while leaving the pre-accelerating ...
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1 vote
0 answers
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High voltage output from CCFL backlight transformer?

I have an old television inverter board I've been meaning to turn into a power supply for a plate-deflected oscilloscope CRT *. I'm not really an expert on transformers, however, and though I have ...
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1 vote
3 answers
233 views

What the heck is a "radiator plate" in a CRT based oscilloscope?

I managed to pickup a used BK Precision 1474 oscilloscope for $10 and figured it would be a good gamble for the price, I powered it up and the CRT had no spot. I did some hunting and managed to find ...
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0 votes
1 answer
378 views

Where is Anode Cap connected in CRT?

On the expanding area of glass? Is inside of expanding area metal?
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12 votes
1 answer
468 views

Troubleshooting a faulty filter circuit in a PAL CRT display

I have an old CRT monitor (Phillips CM8833) which I am attempting to repair. When displaying a composite PAL signal, it only shows a black and white image, but it is still able to display RGB signals ...
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  • 373
4 votes
2 answers
478 views

TV flyback transformer replacement without RC snubber?

I need to replace the flyback transformer on my Atari SC1224 CRT monitor. The flyback I removed from this monitor has a model number of Kf4825G, and has an RC snubber attached to it, which does not ...
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4 votes
3 answers
576 views

Coating within CRT

I have noticed that a lot of CRTs have a coloured coating inside of them that would appear to have practical purpose other than maybe protecting the aquadag. Paints and plastics tend to be avoided in ...
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0 votes
1 answer
202 views

Where can I get a display screen with 30 Hz or less refresh rate? [closed]

I am experimenting with a camera recording a display screen. Based on what I have read - camera recording a screen will have flicker if the refresh rate and frame rates are not synced. My mobile ...
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0 votes
1 answer
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Could black-and-white CRT-based television sets be damaged by holding a magnet to the screen?

I know that it is possible to cause permanent (or at very least lasting) damage to some color CRT-based TV set by holding a magnet close to the screen and distorting the picture. SPECIFICALLY: it is ...
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0 votes
2 answers
780 views

Old portable CRT TV power socket

I found a nice old portable CRT TV (model "tele star 4004") without a power cable. The power socket on the back has six pins: I've never seen such a design before (and google is coming up short). ...
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3 votes
0 answers
8k views

CRT TV NOT TURNING ON [closed]

I'm a beginner in electronics repairing and I need help troubleshooting a tv which doesn't turt on, neither the power LED lights up. The board is a cheap chinese (check the attached image). When I ...
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2 votes
0 answers
286 views

Replace filtering(?) capacitor on CRT deflection Board

I am doing partial recap on CRT monitor Sony PVM 20m2e. (monitor was working, but RGB lines at the top of screen which should be hidden were visible and geometry is not top notch) I desoldered C584 ...
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