RCA Portable CRT TV - video signal and tuneup guidance - Page 1
Forum section: electronics / projects

author: prestonian
author_rank: Newbie
timestamp: April 11, 2022, 10:05:51 pm
content: Hello,I acquired a working RCA portable color television (model number is worn off label).How can I get some video running on this unit? It has VHF/UHF/ANTENNA input. I imagine that I can buy a modulator/converter of some sort?Are there any technical health checks I should perform before putting it into service?I understand that the technical considerations for maintaining and servicing these televisions is a huge domain, but I'm very interested in becoming a steward of the technology and would appreciate any resources or material to start off with.Thanks

author: james_s
author_rank: Super Contributor
timestamp: April 11, 2022, 10:14:18 pm
content: What you need is called an RF modulator, you should be able to find one on ebay or at a thrift store fairly easily. An old VCR will work too. I wouldn't mess with it unless you try it out and it isn't working properly, if it ain't broke don't fix it.

author: BrokenYugo
author_rank: Super Contributor
timestamp: April 11, 2022, 11:03:32 pm
content: RF modulator and cheap 300-75 matching transformer (attach to the the VHF screws).

author: Terry Bites
author_rank: Super Contributor
timestamp: April 12, 2022, 11:10:20 am
content: TV modulatorshttps://www.ebay.com/itm/183760647062?hash=item2ac8fcf396:g:5tcAAOSwaGhcpQmIabound on ebay etc- the problem will probbably be getting an anlog source to drive it.

author: GLouie
author_rank: Regular Contributor
timestamp: April 12, 2022, 04:09:57 pm
content: Assuming this is North American NTSC, another option to use the TV is to look for a north american digital TV converter. When the USA transitioned to DTV, converters were offered to convert over-the-air digital TV to the old analog RF channel 3 or 4, which you can hook to the old TV antenna input. Mine has a coax RF output, so in this case the OP would need a simple 75 to 300 ohm "balun" transformer. This assumes OTA DTV broadcasts are available. I find old rabbit ears work OK in my urban area.I think you can find converters from HDTV to analog composite/S-Video/RGB, plus the RF modulator, would also allow viewing. Sound might have to be handled separately.This TVs might have a host of age-related problems from bad caps to cracked solder joints and anything in between. Do note that the CRT probably has about 20kv on it and the deflection yoke several kv, which can be dangerous if you try to do any physical alignments.

author: Bicurico
author_rank: Super Contributor
timestamp: April 12, 2022, 04:55:47 pm
content: Most TV'd have a Compositor Video plug, solder Pad for Thaís plug or at least a trace to feed Compositor Video in.Otherwise you need a modulator that takes a composite video input and outputs a modulated RF signal. Some VCR, Sat receiver, etc. Used to have a modulator built-in.Anyway, I would say that you can get an old CRT with composite video for free, so don't spend money on a modulator or similar.

author: CaptDon
author_rank: Super Contributor
timestamp: April 12, 2022, 05:15:56 pm
content: The power supply in that unit is basically rectified A.C. line equal to about 145vdc, The 12vdc input drives an inverter that generates 145vdc. Those were nice little T.V.'s in their day and were common on bigger pleasure boats and RV campers. If you have a VCR it probably outputs on Ch3 or Ch4 analog and often VCR's have a direct video in which may possibly pass 'out' through the same built in modulator.

author: james_s
author_rank: Super Contributor
timestamp: April 12, 2022, 05:33:25 pm
content: Quote from: Terry Bites on April 12, 2022, 11:10:20 amThat's no problem at all. DVD players are plentiful, even old VHS machines and laserdisc players are not too hard to find still. If you want OTA there are the digital converter boxes that they made many millions of during the transition to digital, Raspberry Pi and similar SBCs have analog video out, classic video game consoles, etc. I must have dozens of sources of analog video in my house.

author: Bicurico
author_rank: Super Contributor
timestamp: April 12, 2022, 06:37:36 pm
content: Quote from: james_s on April 12, 2022, 05:33:25 pmIt's not the analog source, it's the RF modulator.This no longer common, but can be purchased as a stand alone device.

author: james_s
author_rank: Super Contributor
timestamp: April 12, 2022, 06:46:54 pm
content: Quote from: Bicurico on April 12, 2022, 06:37:36 pmThese are cheap and plentiful, I still see them at thrift stores regularly and there are hundreds of them on ebay, this is just one random example:https://www.ebay.com/itm/234249112857

author: BrokenYugo
author_rank: Super Contributor
timestamp: April 12, 2022, 07:05:49 pm
content: Quote from: Bicurico on April 12, 2022, 04:55:47 pmLack of 12 volt supply option on a TV this size suggests to me that this likely a "hot chassis" set with a non isolated supply, you can't just add a composite jack unless you don't mind mains riding on it.

author: CaptDon
author_rank: Super Contributor
timestamp: April 12, 2022, 08:33:23 pm
content: Yugo, Did you read My post? I remarked how the internal power supply actually operates. It is hot chassis and it DOES have a 12vdc input option.Look at the O.P.'s picture of the model/serial/power sticker. The power plug has several pins and a 'bump' so you can't insert the plug wrong. The T.V. came with a 120vac power cord and a 12vdc power cord, although most folks lost one or the other. Which ever one they didn't use got pitched. I worked on several of these, generally coming from the local marina or the 'Carnies' when the carnivals were in town. They are HOT CHASSIS and as you mentioned NOT suited for direct video input tied to chassis. The antenna inputs are isolated via baluns.

author: prestonian
author_rank: Newbie
timestamp: April 14, 2022, 10:51:51 pm
content: I'm back with an update. I obtained an RF modulator and transformer. It took time to arrive at the connection scheme shown in the attached photo. Nothing worked well until I connected a jumper between the ANT and VHF (for reasons I don't understand). Then everything kicked in. After some adjustments to the color/picture knobs on the front of the unit, I arrived at a very crisp picture (Xbox source) with nice color.I decided to take a look inside the chassis. It's not a pretty sight (dust and spiderwebs). Photo attached.Finally, about 75% of the line cord is wrapped in electrical tape. I'm inclined to replace it.