How to convert the TV in my boombox? - Page 1
Forum section: electronics / projects

author: optonox
author_rank: Newbie
timestamp: November 18, 2018, 10:44:47 am
content: Hi,hereis a picture of my boom box with built-in analog TV.Is it possible to somehow get the TV in this to connect to a composite video cable - or is there some other way I can control the TV signal that comes out of it?Thanks for any help.

author: Bratster
author_rank: Frequent Contributor
timestamp: November 18, 2018, 07:10:32 pm
content: Get an RF modulator, then you can put composite video and audio into that and send the RF output into the antenna port on your boombox.As long as it can tune in TV channel 3 or 4.Something like this:RCA Compact RF Modulator (CRF907A)https://www.amazon.com/dp/B0014KKV7WSent from my Fi Moto x4 using Tapatalk

author: Ian.M
author_rank: Super Contributor
timestamp: November 18, 2018, 07:39:32 pm
content: It will still be a crappy mono CRT display, with very questionable reliability (as its got to be something like 30 years old), so IMHO the best option would be to totally remove the CRT assembly and remove or disable any associated HV circuitry, storing the parts if you ever want to be able to restore it to collectable condition, then figure out how to integrate a touch-screen media player running Android.

author: james_s
author_rank: Super Contributor
timestamp: November 18, 2018, 08:06:36 pm
content: What's with this stupid trend of hacking up classic stuff and installing crappy touchscreens in everything? If you want a touchscreen Android device, just carry around a tablet. The CRT is the only unique aspect of those old portable setups. They are actually quite reliable, the only fault I can recall ever encountering was a bad electrolytic capacitor and that was in a cheap Chinese B&W set that had a lot of hours on it.Mose of those inexpensive B&W TVs were based on one of just a few ICs that handled all of the video processing. Many of the TVs had composite input but some did not. If you want to add it to that TV the first step is to look at what IC is in it and then find a datasheet. If you are lucky, the components to handle the composite input may already have locations on the board you can populate.

author: Ian.M
author_rank: Super Contributor
timestamp: November 18, 2018, 09:21:07 pm
content: Well the original idea was you could go somewhere, and take easily portable entertainment with you: Music, radio or even watch a broadcast ball-game. It was never the device of choice for sitting around watching cable.The TV signals it uses are no longer transmitted, and the need for a separate signal source outputting composite video (and maybe a modulator if you don't want to mod the boombox for a composite video input) removes the easy portability advantage.Modding it to add an Android device is the nearest you'll get to its original functionality, if there's a livestream of the events you want to watch.Of course its a very niche concept, and I personally would rather use a phone or tablet + good bluetooth speakers, and sell the boombox to a collector who will value it in orginal condition.

author: Whales
author_rank: Super Contributor
timestamp: November 18, 2018, 10:03:47 pm
content: Please don't convert it into a tablet case. Intentions about 'original function' aside the consequences would be nothing different.RF demodulator cans sometimes have composite video outputs. Otherwise you can try and follow the RF can's output to other chips on the board and see if they output composite video.If you don't have any easy way to ident composite video: I'd plug a composite cable into another TV and use it as a 'probe'. Worth putting something like a 1K resistor + 100nf or smaller cap in series with it to reduce the risks of damage. Don't do this if you think it's too cramped and near HV bits, however, use your judgement, I have no clue what it looks like inside your unit.

author: james_s
author_rank: Super Contributor
timestamp: November 18, 2018, 10:41:56 pm
content: These will all have standard composite video in there somewhere, like I said initially, look for the big IC on the TV board and then look up the datasheet. Almost all of this sort of thing have a separate TV chassis in there, I've never seen it all fully integrated into the main unit. The TV will likely be based on one of two or three different ICs and will be a very basic unit.Personally I have an old rackmount agile modulator that I use as a TV transmitter in my house, I just select a channel frequency and connect a composite video source and I can pick up the signal on any of the old TVs I have.B&W CRTs have a unique look that is not really replicated by any other technology. It looks especially cool watching old shows that were made in that format.

author: optonox
author_rank: Newbie
timestamp: November 19, 2018, 12:03:14 am
content: So, assuming I do not go the touchscreen route:The basic steps to get started are to unscrew as much as possible and try to find the "IC" that goes to the TV?By "IC" you mean integrated circuit - right? Can someone provide me an example of what I am actually looking for? What does it look like?

author: Whales
author_rank: Super Contributor
timestamp: November 19, 2018, 07:46:26 am
content: There will be many ICs, and they come in all shapes/sized/brands. You are after one that sits between the RF can and the big chips acting as amplifiers before the tube.Sidenote: it sounds like you might not be familiar with CRTs. CRTs have unusual high-voltage hazards, even after you have turned them off and unplugged them. If you're not familiar then please do some research about this and how to discharge them.

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2018, 05:02:03 pm
content: Whatever you do the first step is to carefully remove the back cover and take a look inside. The TV will almost certainly have a distinctly separate chassis which is connected by a few wires to the rest of the boom box.CRTs do use high voltages but a little tube like this will have an anode voltage of only about 6kV at a few microamps. It will hurt if it zaps you but extremely unlikely to cause any real harm. Just be careful poking around blindly.

author: N2IXK
author_rank: Frequent Contributor
timestamp: November 20, 2018, 04:30:05 pm
content: With a schematic, it should be relatively easy to find a point after the video detector to inject your composite signal. A standard composite video signal is around 1 VPP into a 75 ohm load, with negative going sync pulses. You may need to invert or level shift your input signal to match the circuitry in the monitor.

author: optonox
author_rank: Newbie
timestamp: April 23, 2020, 09:39:07 am
content: I should update this with:There is no BNC connector input in this boom box.The only video input option is "antenna in" which I am assuming is if I plug in one of those satellite dish looking antennas.Is there any devices that take component video in and output an RF signal (transmit the RF signal, not over coax)?

author: james_s
author_rank: Super Contributor
timestamp: April 23, 2020, 08:42:04 pm
content: I wouldn't expect a BNC, they were only used on pro gear."Antenna" would have traditionally been a telescopic whip, a pair of "rabbit ears" or a rooftop Yagi, ie the classic outdoor TV antennal. Satellite dishes were rare in that era.What you describe is called an RF modulator. Any RF modulator can transmit over the air if you connect it to a suitable antenna instead of using a direct cable from the modulator to the antenna jack. The professional ones are typically higher power but even a cheap one will work at close range. It's not going to be as powerful as a real TV transmitter but it's not legal to transmit at high power anyway. Look for brands like Holland or Blonder-Tongue, surplus professional broadcast gear.