CRT TV, Telesensory Rainbow....Dead!!

[Andyd1970]

Hi Guys,

I have been asked by a local care home to repair a Telesensory unit, it is used by a mentally ill blind resident of there care home.

I said no problem to help out but I cant find the cause yet. Basically the unit is dead, I am getting power to the light below the CRT that is used to illuminate the newspaper/document.

So thought I would ask you guys to see if anyone can help me with some fault finding on a CRT.

kind regards

Andy

[tom66]

Re: CRT TV, Telesensory Rainbow....Dead!!

My guess would be these are two power supplies one for the fluorescent lamps and one for the CRT monitor. The left one is for the bulb, right is for the monitor.

https://www.badcaps.net/forum/attach...0&d=1370446733

The CRT looks like it only has a single voltage requirement so check if that is present, see if the rating is labelled. But possibly around 100~150V DC if it is straight B+ for CRT... Could also be a 12V or 24V monitor.

For a device which people depend on this is quite poorly made, I am very disappointed! Seriously, these units are not cheap, so you would expect they would put better components into them, and better care into assembling them.

[Andyd1970]

Re: CRT TV, Telesensory Rainbow....Dead!!

Hi, On the last picture you will see a black/red pair that goes to a PCB on the side of the unit. I unplugged that cleaned contacts and refitted it and hey presto it worked!! It worked for a good few days swtiching it on and off, until today I switched it as I was going to return it I heard the sound of the screen energising but no picture. so I switched it off and tried again later and now no sound as the screen energisies. The lights operate that are used to illuminate the newpaper etc.

Suggestions? Tom made reference to some things but sure where they are likely to be to check.

Andy

[Elysarian]

Re: CRT TV, Telesensory Rainbow....Dead!!

The sound as you switch on is likely the degaussing circuit operating (this is usually controlled by a PTC device in series so it only operates for a split second at switch-on from cold).

What this means is that the CRT's board is getting power - can't see what's under there but my initial investigation would be centered around the line output transistor and associated circuitry (these often fail short and cause a cascade failure in the SMPS or, if you're lucky, fail open and replacement will fix the fault).

You should also check for dry joints around the line output (flyback) transformer if the fault is intermittent as quite a number of the necessary voltages inside a TV are generated from that.

[goontron]

Re: CRT TV, Telesensory Rainbow....Dead!!

did anybody notice this choke is burnt?
could you take pics of the bottom of the board

[tom66]

Re: CRT TV, Telesensory Rainbow....Dead!!

Is it? Just looks like varnish to me.

[R_J]

Re: CRT TV, Telesensory Rainbow....Dead!!

I would check for poor solder connections near the plug you cleaned, I don't think cleaning it did anything but removing and reinstalling the plug possibly caused the bad connection to work for a bit.

[ben7]

Re: CRT TV, Telesensory Rainbow....Dead!!

did anybody notice this choke is burnt?
could you take pics of the bottom of the board

Either way, are those Elna audio capacitors in an smps?! The two just under that inductor.

[tom66]

Re: CRT TV, Telesensory Rainbow....Dead!!

Either way, are those Elna audio capacitors in an smps?! The two just under that inductor.

...Elna make a LOT more than audio capacitors. They also make low ESR capacitors suitable for SMPS.

[Andyd1970]

Re: CRT TV, Telesensory Rainbow....Dead!!

Hi Guys,

Thank you for all the input, so far I have checked for dry joints on the PSU, I have reflowed the 12v pins on the PCB that the PSU feeds that is located on the side of the unit. See pics of the two PCB's.

I checked that the PSU was outputting 12v to the side PCB and it is. The light system works but I guess thst is driven by the other PSU.

Andy

[Andyd1970]

Re: CRT TV, Telesensory Rainbow....Dead!!

Hi Guys,

I reflowed all the points on the PSU and the connector on the side PCB where the 12v goes in, still dead but I do get the screen degausing when I switch it on after it has been of for a while.

[tom66]

Re: CRT TV, Telesensory Rainbow....Dead!!

The CRT takes 12V? So do you have 12V when it powers up?

[ben7]

Re: CRT TV, Telesensory Rainbow....Dead!!

We are looking in the wrong spot. You can see in the first picture, white and black wires (neutral and line) going to the crt board. That is the board we need to look at.

Look on that board for burn marks, bad solder joints, or blown fuses. Test all fuses. Could you take some good pictures of that board, bottom side and a few different angles of the top side, please?

Also, have you tried un-plugging the 12v cable from the power supply, then plug it back in? Could be a bad connection on the connector contacts.

[Andyd1970]

Re: CRT TV, Telesensory Rainbow....Dead!!

Hi Tom,

I say 12v as the right hand PSU outputs 12v at switch on and the PCB to the side it feeds (see pictures) has 12v written on the PCB. I can hear a sort of low sound like a creaking sound from the rear of the monitor/PCB below it.

[Andyd1970]

Re: CRT TV, Telesensory Rainbow....Dead!!

Hi All,

Sorry to be a pain, but the care home are desperate for this back and cant afford a new one as they are soooo expensive. I have tried a few things but due to the voltages on the PCB I am not confident where to start, if it was an LCD I would be much happier due to Tom66's excellent advice.

Andy

[tom66]

Re: CRT TV, Telesensory Rainbow....Dead!!

May I suggest you offer an alternative?
A Raspberry Pi computer (£30), plus webcam (£10) plus HDMI/DVI LCD monitor (£60) can do the job of this device for around £100.

Repairing it may be very difficult, I have no CRT experience, and without schematics, it may be nigh impossible.

[goontron]

Re: CRT TV, Telesensory Rainbow....Dead!!

May I suggest you offer an alternative?
A Raspberry Pi computer (£30), plus webcam (£10) plus HDMI/DVI LCD monitor (£60) can do the job of this device for around £100.

you say raspberry PI, oh no here come the linux devs since you need to be one to get that thing setup

[Andyd1970]

Re: CRT TV, Telesensory Rainbow....Dead!!

Hi, Goontron,

I saw you mnetioned about the choke which to me looks OK, I did take some pictures as per your request, do you have any thoughts. I apriciate TOM66's suggestion, but the thing is the guy has used this for years and only wants this back. So I am trying to do all I can to help.

Andy

[tom66]

Re: CRT TV, Telesensory Rainbow....Dead!!

you say raspberry PI, oh no here come the linux devs since you need to be one to get that thing setup

No, you do not. I have set one up and it is easy as pie, seriously, blow an image to an SD card, launch video cam app, connect camera & you are done.

[goontron]

Re: CRT TV, Telesensory Rainbow....Dead!!

No, you do not. I have set one up and it is easy as pie, seriously, blow an image to an SD card, launch video cam app, connect camera & you are done.

really? i had one when the project first started and it was CLI. its GUI now?