Sony KV-M1420U Television - No Colour

[mlv]

Our Sony 14" KV-M1420U television has suddenly lost its colour.

The picture is still perfect, but in monochrome. Sometimes the colour will return if the television is switched to 'off' or 'standby' and then switched back on. When the colours fails, it changes instantly from colour to black & white, as if a switch had been operated. There is no gradual fade.

The various on-screen control icons and the channel numbers still retain their colour (light green), even when the picture is in black & white.

As it's a Sony, I suspect dry joints. I also hope that the specific nature of the fault will point to a particular board or component that I can repair myself.

Can anyone give me a simple guide as to what might be the faulty unit and where it is located?

TIA

[Dave Stanton]

From the way you speak, of dry joints and Sony, are you in the trade ?

Dave

[The Natural Philosopher]

Mm. ALL color lost, not just one gun eh...

Sounds like maybe whatever picks out the color subcarrier is packing up.

Is teher a crystal in there somewhere? That runs teh PAL side of things? They occasionally give up and stop osscilatng.

I had a non sony set obnce that required a thump to get the odd color back. I opened it up and dicoivered zillions of eyelets instead of through plated holes. I resolderd every one.

Set worked another 5 years faultlessly, till it got struck by lightning...

[mlv]

No, but I have yet to own a Sony television (or radio, for that matter) that doesn't suffer from a dry joint problem once it's a few years old.

When my 21" Sony TV started playing up a while back, the technician that repaired it said he found 47 dry joints. My previous Sony TV suffered dry joint problems on two separate occasions.

Dry joints do seem to be synonymous with Sony.

The 14" TV isn't worth as much as a Service Centre would charge for the repair, so if I can identify the likely fault, I'll have a go at repairing it myself.

[mlv]

Yep, all colour lost - a perfect black & white picture.

Could be - I'm hoping someone will tell me.

The tradition thump does not bring the colour back on my 14" Sony.

[OldScrawn]

[Bob Minchin]

Mike,

are you sure about that model number? I have a sony 14" manual here and all the variants are KV-141

The UK model with UHF tuner is KV-14T1U (M indicates a vhf/uhf tuner)

If your set is similar to mine then look out for a 40 pin chip MC44007P which is the Chroma processor which has a crystal running at 4x the colour subcarrier eg 17.734 MHz. One end of the crystal connects to pin 33.

HTH

Bob

[mlv]

Yes, the model number is KV-M1420U (S/N: 6043B75). The manual listed three model numbers, so I took the details off the TV rating plate. I've had the TV a while, maybe 12-14 years!

This MC44007P chip, is it plug in or soldered? Are you suggesting the chip might need replacing, or that I should check for dry joints at its pins? Or is a faulty crystal more likely? Assuming I have the back off the TV and am looking inside, where is the PCB carrying this chip most likely to be located?

The fault has gone away for the past three days and the television is working normally with good colour at the moment. I'm sure the fault will return.

Thanks for your help.

[Bob Minchin]

Hi Mike,

It does sound like you have a model not covered by my service manual. From memory mine Tv is about 6 years old. I mentioned the the part number of the chroma processor simply to help you find the crystal. Once located you could check to see if it is oscillating. I don't know if you have the right sort of test equipment for this anyway or indeed would recognise a crystal.

As you say it is now working I would suspect dry joints. I doubt if the ICs are socketed but if they are, dirt or corrosion on the pins can be an issue. If you are comfortable with using a fine soldering iron, then reheating joints in the region of the colour crystal could do the trick.

Try

and search for Crystal to see pictures of a crystal - usually silvery metal cans , sometimes with plastic sleeves.

frequency will be a multiple of 4.433MHz either 1x 2x 3x or 4x

HTH

Bob

[Mathew J. Newton]

I've got a KV-M1421U (teletext version of yours?) with *exactly* the same problem. I haven't got round to attempting any fix yet but I did some web hunting and it would appear, as others have said, that dry solder joints are common culprits for this problem.

Looking at the Usenet posting at

echos the suggestions of others in this thread of resoldering the crystal. I will give this a shot next week and let you know how I get on.

Incidentally, I can confirm that my teletext remains in full colour, as per the description in the above URL so hopefully we could be onto winners here!

Cheers,

Mat

[Nigel]

"mlv" wrote in news:c0801k$ekb$ [e-mail]:

This is usually caused by trimmer CT332. You can either clean and adjust it, or replace it with a 15pF capacitor.

[Keiron Carroll]

In message , Nigel writes

Nigels' right here. It's a common fault. You'll see a small 'pot' next to the crystal. Note what position it's in now. With a trimmer tool, or very small screwdriver just give it a tweak and your colour will come back They go int 'dead spot' . You can put it back to it's original position and your probably going to be o.k. Ideally a new oscillator trimmer should be fitted but you'll probably be o.k. Although the crystal osc itself can cause this problem and is common on other makes, on these Sony's it always seems to be this little bugger.

Hope this helps,

Keiron

[mlv]

Keiron Carroll

????

Thanks for the information guys. Next time the colour goes (it's been fine for the last week or so) I'll give CT332 a tweak.