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Old 2nd Feb 2019, 11:35 pm   #1
19Seventy7
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Default Odd image

I have bought a 5.5 inch B/W TV (working, kind of) to be able to watch TV and use some games consoles whilst my Hitachi is in its current state.

I have just received my adapter, coax to 3.5mm and i plugged my VCR and i have been met with an odd image.

Could this be convergence or is something else faulty?

The first image is just a solid colour, the second a frame from a tape and the last, no signal, just snow.

Thanks
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Old 2nd Feb 2019, 11:41 pm   #2
60 oldjohn
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Default Re: Odd image

What make, number of TV is it ? Also what VCR?


John.
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Old 2nd Feb 2019, 11:48 pm   #3
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Default Re: Odd image

Its a Maxim 5.5 inch TV. (Its a generical, various branded TV)

Model number: MX11-07

VCR: LG LV210 (VCR isnt too great, but doesnt have the “waves” issue on other TVs

Thanks
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Old 3rd Feb 2019, 12:46 am   #4
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Default Re: Odd image

It needs a new capacitor
Same saga again but this time it is the power supply.
There is loads of mains ripple.
It could be a series regulator if it has one such as 12 volt sets do.
The picture looks about the right size so the regulator is less likely to be the problem.
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Old 3rd Feb 2019, 12:57 am   #5
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Default Re: Odd image

Oh... great.

It is a 12v set so there is chance. I’ll leave the set off. How would i know what capacitor if i cant find a schematic or diagram?

Thank you for your reply.
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Old 3rd Feb 2019, 1:01 am   #6
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Default Re: Odd image

It will be the big one next to the rectifier and mains transformer. If it has been used in 12 volts for a long time in a caravan (cumbersome car accessory) or such like it may not have been noticed.
Try it on batteries and if it is all right then it is the big capacitor in the power supply.
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Old 3rd Feb 2019, 1:12 am   #7
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Default Re: Odd image

That looks like hum bars, caused by excessive ripple on the power supply. You'll notice the wavy edges on the picture, visible even when there's no signal from the VCR (the 'snow' looks ripply, too.)

These small TVs use a separate plug-in power supply, also called a mains adaptor, AC adapter or 'wall wart'. This is the first thing to suspect. Try another power supply. It's a 12 volt TV, so see if you can find another 12 volt DC power supply in your house. They're common on things like internet modems / wireless routers, external hard drives, other small LCD TVs and PC monitors. Just borrow the power supply from the other device and plug it into your TV, then see if the results are any different.

Before using another mains adaptor, check the rating is 12V DC and 500mA or greater e.g. 12v 1000mA or 12v 2A. The output plug needs to be centre positive - usually marked like this:

(-)---(o---(+)

These days it's rare to find centre negative power supplies, where the + and - are the other way round, but I have to mention it. The wrong polarity will most likely mean your TV will not work at all, and could be damaged.

You could also test your TV using batteries instead of a mains adaptor, if you happen to have enough suitable batteries lying around ( 8x C cells, usually), but it's probably not worth buying a set of batteries specially for testing. Try using another mains adaptor first.
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Old 3rd Feb 2019, 1:50 am   #8
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Default Re: Odd image

Quote:
Originally Posted by Refugee View Post
It will be the big one next to the rectifier and mains transformer. If it has been used in 12 volts for a long time in a caravan (cumbersome car accessory) or such like it may not have been noticed.
Try it on batteries and if it is all right then it is the big capacitor in the power supply.
Oh, so its most likely to be the plug itself, and not the actual TV?

The seller did in fact have it in a caravan. I probably have some more 12V adaptors up in the loft amongst christmas decorations so i can try one of them as Hamid suggested.

If that doesnt work, ill search for some C batteries and try that.

Ill report back tomorrow whats happened with a different adaptor if i can find one.

Thanks

Quote:
Originally Posted by hamid_1 View Post
That looks like hum bars, caused by excessive ripple on the power supply. You'll notice the wavy edges on the picture, visible even when there's no signal from the VCR (the 'snow' looks ripply, too.)

Before using another mains adaptor, check the rating is 12V DC and 500mA or greater e.g. 12v 1000mA or 12v 2A. The output plug needs to be centre positive - usually marked like this:

(-)---(o---(+)

These days it's rare to find centre negative power supplies, where the + and - are the other way round, but I have to mention it. The wrong polarity will most likely mean your TV will not work at all, and could be damaged.
As you said, the snow is ripply too. There are what i’d call “bubbles” on either side of the screen.

If the adaptor isnt marked (-)—-(o—-(+) how would i know? I guess if its marked as (+)—-(o—-(-) is negative?

Thanks
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Old 3rd Feb 2019, 2:26 am   #9
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Default Re: Odd image

You can test the mains adaptor with a multimeter.

Set the meter to DC volts. (20v range or higher. Black lead connected to COMmon terminal on meter, red lead to volts/ohms.) Touch the red probe to the centre of your mains adaptor's output plug and the black probe to the outer metal part. Observe the reading on the meter.

A regulated power supply should read 12 volts. An unregulated one (as originally supplied with the mini TV) will give a higher reading, probably around 16v. If the power supply is centre negative, the multimeter will read -12v ( that's minus 12v) or around -16v instead. If the mains adaptor is far outside the range of 12-16v, it's unsuitable for your mini TV.

Since you mentioned you have Virgin Media, you can try the power supply from their Super Hub - I'm pretty sure it will match the requirements of your TV.
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Old 3rd Feb 2019, 2:56 am   #10
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Default Re: Odd image

Although with a faulty (reservoir) capacitor, it may well still give a reasonable reading off- load with a multimeter, but the humbars on the picture suggest it is faulty.
The good news is it's definitely not a convergence fault, as it is a monochrome set and convergence only applies to getting the three beams to align on colour sets!
I have a similar set bought from Woolworths about 12 years ago (for about £10, I couldn't resist: I'd always wanted a USSR Vega 5" set, but they were getting expensive second-hand), used it for an hour to see that it worked, put away as an emergency spare for when my main TV and the spare failed, but, meanwhile, analogue TV was switched off and Work threw out a decent LCD 19" ex-CCTV colour monitor, then my set-top boxes and DVRs didn't have RF out, and I ended up buying a 32" widescreen LCD TV new from ASDA for £149 a couple of years ago...

Last edited by G8UWM-MildMartin; 3rd Feb 2019 at 3:07 am. Reason: extra waffle
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Old 3rd Feb 2019, 3:08 am   #11
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Default Re: Odd image

Yes, a multimeter alone may not detect a faulty mains adaptor, that's why I suggest trying a different mains adaptor. The multimeter test will hopefully rule out any unsuitable adaptors from being used, which could damage the TV.

Just to add, if you want to try a mains adaptor from something else like Christmas lights, make sure it is DC output and not AC. Some Christmas lights adaptors give AC output, marked 12v~ (wavy line) instead of a solid line with dashes which means DC. An AC-AC adaptor will not have a polarity symbol marked on it, either. I'm wondering if the seller gave you the wrong mains adaptor by mistake.
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Old 3rd Feb 2019, 3:38 am   #12
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Default Re: Odd image

I will look tomorrow at adaptors to make sure they are DC. I did wonder myself if the adaptors have been mixed up. If they have could the TV be damaged?

Thanks
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Old 3rd Feb 2019, 4:04 am   #13
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Default Re: Odd image

From the pictures, the TV doesn't seem obviously damaged but the power supply you used was either rated for too low a current or defective.
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Old 3rd Feb 2019, 2:50 pm   #14
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Default Re: Odd image

Oh thats good i guess. Power supply should be fairly easy to find.

Thanks
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Old 3rd Feb 2019, 3:04 pm   #15
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Default Re: Odd image

Update: the adaptor is 12V —- 400mA and the input is 230v~

Thanks
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Old 3rd Feb 2019, 3:37 pm   #16
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Default Re: Odd image

I don't know how similar the internals of your TV are to the Nikkai-badged one that Maplin sold, but in that one, there's a 470uF capacitor (C400) on the main PCB (inside the set) across the incoming power, and also a 2200uF capacitor in the mains adaptor. The mains adaptor is a simple unregulated thing (transformer, bridge rectifier, smoothing capacitor) giving around 16V.

There's also a 2A fuse inside the set in series with the incoming +ve line. While I doubt it draws 2A, it may suggest that a 400mA adapter is not going to be able to supply enough current.

I traced out the circuit of the Nikkai one (hand-drawn as ever for me). If anyone wants a copy, please PM me. It's a 3MByte .pdf so too large to post here.
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Old 3rd Feb 2019, 3:40 pm   #17
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Default Re: Odd image

Quote:
Originally Posted by InsertNameHere View Post
Oh thats good i guess. Power supply should be fairly easy to find.
Yes, most of us have various spares, and 12V centre positive is fairly common.

I recently had the situation where my ADSL router suddently stopped working, and I was mightily relieved to find that it was the plug-in power supply (wall wart) that was faulty - despite giving a satisfactory output reading on a multimeter. Swapping for another wall wart brought it back to life.

One other thing to beware in addition to the polarity is that there are almost endless varieties of those concentric power plugs, some of which look nearly identical but may have different-sized centre pins and/or outer diameters. You can sometimes (just about) get away with a plug with a large-pin hole on a socket with a small centre pin (though you may get an intermittent connection), but a large pin won't go into a small hole!
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Old 3rd Feb 2019, 3:57 pm   #18
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Default Re: Odd image

I'll keep an eye out for that, I have no idea where I'm going to get a power supply as I don't actually have any others.

All the Christmas decorations have the typical MK plugs. I'll message the seller now to see if he has given the wrong plug and could swap.

Thanks for your help, much appreciated.
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Old 3rd Feb 2019, 4:43 pm   #19
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Default Re: Odd image

Quote:
Originally Posted by InsertNameHere View Post
Update: the adaptor is 12V —- 400mA and the input is 230v~
I think this is the problem - the current rating 400mA is too low.

I've found a photo of an identical set - see attached. On the back it says Power 12v DC 1000mA. Double-check what yours says, but I'm pretty sure it will need more than 400mA.

By all means, ask the seller if he/she can exchange your power supply for the correct one, but if not, they are very easy to obtain. Many electronic items such as internet routers use 12v power supplies rated 1000mA or more. Millions of thse power supplies have been made. Many are sitting unused in people's houses since they've stopped using the device they came with. Ask any friends / neighbours if they have any that they don't want.

Remember, the current rating of the power supply can be higher than that required by your TV, e.g. 1500mA, 2A - it won't do any harm, but the voltage needs to be be the same.
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Old 3rd Feb 2019, 4:44 pm   #20
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Default Re: Odd image

Quote:
Originally Posted by InsertNameHere View Post
I'll message the seller now to see if he has given the wrong plug and could swap.
Failing that, they are available for under a fiver, such as this one from eBay. This is just one that a search threw up. Other suppliers are available, and may have cheaper offerings.
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Last edited by Dave Moll; 3rd Feb 2019 at 4:46 pm. Reason: quote added for clarity as hamid 1 and I cross-posted
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