Miniature 5" B and W TV

[Pete_kaye]

I was given a used caravan/kids Tv which worked Ok for about an hour then the picture disappeared although the sound and radio part still work fine.the screen is completely blank >i don't know the maker but it has a label of the sellers as HHS trading Manchester.It has a blue clear plastic case and runs from 12 volts or via mains adadptor.
Anyone recognise it or the fault? I don't know much about Tv's but happy to proceed with caution.

[Nickthedentist]

Basic things first... are the tube heaters lit? Look for a dull orange glow in the tube neck. You'll need to look in near darkness.

Nick.

[Pete_kaye]

I am at work right now and Tv is at home but any more hints or directions to useful info would be helpful .

[KeithsTV]

I have a 5" TV, bought at a local supermarket a few years ago. Its performance under strong signal conditions (we live within sight of Emley Moor) is pretty poor but it came with a circuit diagram which I can scan it and send it to you if you wish. I think these Chinese made TVs are very similar. There was also some information on common faults, which unfortunately didn't include a no picture fault, in the July 2004 issue of Television.

Keith

[Pete_kaye]

I have removed set from cabinet and,in complete darkness, can see two tiny red lights in the end of the tube and also some light in the 4 corners of the screen only .There is a set of dark bands across when I tune to station .After 3 minutes there was distinct acrid smell so I switched over to the radio part and it subsided .I noticed a small 2A fuse which was intact but looked a bit brown.Everything else looked Ok .Are there any places that are dangerous to touch eg tube?

[arjoll]

Maybe dodgy capacitors - are any of the electrolytics looking distressed?

[Steve_P]

I've not got the circuit, but I would want to know that the heater volts were right, and this would probably lead to the Line Output Stage and Line Oscillator stages. It will probably have a diode split LOPT, and I would start by replacing the transistor associated with this. The Line Output Transistor.

Something has gone low in volts or value. What and why, I don't know without seeing the set or the circuit.

Cheers,

Steve P.

[KeithsTV]

Here's the circuit of the TV I have plus info from the television article. If the tube heater is on, the 10.8v supply is present although it may be low - check the voltage. I guess there may be a problem with the line output stage possibly a shorted diode. The 90v supply for the video output may be low which would affect the 1st anode supply and may cause a dim or non existant picture.

Keith

[Pete_kaye]

I have decided to offer this set for FREE in The 'For Sale' section.

[matthewhouse]

Hello, I am now the owner of this TV and have got it working as such.

After connecting the tube to a scrap chassis of the same type I was able to get a picture. I did not want to swap my scrap chassis for the original one as mine had been modified no end by me about 5 years ago and the radio PCB had snapped. The LOPTr was getting red hot and checking, fitting components in the working chassis proved that it was good as were many other parts. As the LOPTx on the good chassis was missing the suction cup connector (i just hooked the EHT wire into the button) i decided to swap the LOPTx the LOPTr was getting red hot and the heater was no longer lit, so I fitted the working LOPTx into the non worker and fitted the suction cup and the TV now works.

However the picture is always snowy even when connected to an external aerial. I will probably swap the tuners over, but is there anything else I should check?

Cheers,
Matty

PS. Thanks Paul for reopening this thread.

[HamishBoxer]

Check the antenna jack also SAW filter

David

[matthewhouse]

Check the antenna jack...

Sorted, thanks. Yep the bit that connects to the tip of the plug had somehow broken off. A replacement from the other board sorted it.

Cheers,
Matty