TV colour comes and goes...

A

Artist 2004

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#1
My ageing Sony TV has been losing colour intermittently over the past year with increasing frequency, both with UHF antenna and equipment connected using SCART, namely VHS video recorder, DVD player, satellite receiver. With some equipment the problem was more acute than others. The problem does not affect system colours, e.g. menus, teletext.

I took it to a local repairer who improved it but not wholly successfully. Unfortunately no-one could explain what he had done.

Now I get colour constantly except when I connect the video recorder. Any suggestions as to the cause?
 
Llew

Llew

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#2
Maybe your repairer just re-adjusted the colour reference oscillator trimmer (a common problem with some Sonys).
If the colour is still dropping out, it could be the associated components around this area (PAL decoder IC) taking the oscillator out of range, or the IC itself.

OSD and Teletext graphics are generated locally and go to the CRT aft of the decoder, as does RGB from your scart, so won't be affected. Does your other equipment use the RGB input of your scart, or composite (CVBS)?

CVBS from your VHS recorder goes to the PAL decoder, which would give the same symptoms as above, but unfortunately doesn't explain why you still have colour from off-air signals. Have you the model number of your Sony?

Llew
 
Llew

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#4
LOL, thought we'd been over the problem before. These Sonys... :-doh! O-Ha
 
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spiney

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#5
just to expand on what Llew said ......

The complete colour image is formed from 3 separate pictures combined (red green and blue). But, these can be "derived" in different ways.

1) The SCART lead - with its many wires! - carries these 3 pictures separately on 3 different wires, in either RGB (straightforward) or YUV (matrixed) modes. You may be able to select which mode, on both tv set and/or SCART connected devices. Which one is used doesn't really matter, it's still really 3 different pictures, and should always give you colour, from any device connected to TV set via SCART.

2) Off air, on analogue transmissions, the tv has to "lock onto" the colour subcarrier (PAL system, in Turkey?), to re-derive the colour signals from transmitted luminance (Y) and chrominance (UV). If it can't "find" the subcarrier, then you'll just get Y, which is the monochrome picture!

It's easy to get Y, over quite a broad tuning range! Getting UV is harder, your tv has to be more precisely tuned. Also, as components age, the "default" frequency of your set's PAL oscillator can drift, and may need re-adjusting to get any "colour lock" at all, almost certainly that's what the repairer did.

(As components age, it may still be possible to get off-air colour by very carefully re-tuning, until eventually this won't work at all!).

3) But, this "subcarrier" version of the colour signal is also on the SCART lead, as a single signal on just one wire. If that mode is selected, then a TV which has problems getting the broadcast subcarrier may also have problems "locking onto" the SCART version, even though the SCART one doesn't involve any tuning!

4) You may still be using the video recorder subcarrier mode output, either in UHF (aerial) or SCART (CVBS) form, rather than one of the 3 wire SCART modes. See if you can change this on setup menus. Or, try carefully re-tuning whichever TV channel you're using for the video recorder output.
 
A

Artist 2004

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#6
Thanks for you interest Llew, and yours Spiney and Gameboy - I've just seen them and haven't had a chance to study them yet. And yes, Turkey uses PAL, but different sound system.

Sony Model: KV-M2151U
VHS recorder SCART o/p is CVBS only.
Satellite receiver SCART o/p is selectable between RGB and CVBS.

I set out today to see if the problem was confined to CVBS as opposed to RBG. Murphy's law kicked in and I had good colour all day on both systems. So I'll give it more time and post results later.

It's likely that the repairer only adjusted something, or replaced a basic component, as it was in a small rural town in Turkey and it was ready next day. If it had needed a Sony component it he would have had to send for it.

Are you able to identify for me where the oscillator trimmer is? I'd like to have a bash at tweaking it.

Cheers.
 
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#8
I had the same TV - I understand that SONY had a problem with this TV but never did admit it 'O'-red

Sound more likely to be the dry join problem to me...

This was the icing on the cake, for me, with SONY. I had a video recorder that would produce blue flecks on the bottom of the picture when recording in long play. After being returned twice to SONY they told me it was 'within tolerance' and not to use long play! :-doh!

I wasn't happy, and the dealer replaced the recorder even after eight months.

Picked a Panasonic and never looked back - perfect picture whatever.
 
Llew

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#9
Artist 2004 said:
Thanks for you interest Llew, and yours Spiney and Gameboy - I've just seen them and haven't had a chance to study them yet. And yes, Turkey uses PAL, but different sound system.

Sony Model: KV-M2151U
VHS recorder SCART o/p is CVBS only.
Satellite receiver SCART o/p is selectable between RGB and CVBS.

I set out today to see if the problem was confined to CVBS as opposed to RBG. Murphy's law kicked in and I had good colour all day on both systems. So I'll give it more time and post results later.

It's likely that the repairer only adjusted something, or replaced a basic component, as it was in a small rural town in Turkey and it was ready next day. If it had needed a Sony component it he would have had to send for it.

Are you able to identify for me where the oscillator trimmer is? I'd like to have a bash at tweaking it.

Cheers.
Sorry, haven't got a circuit board layout, but here's the schematic of the chroma IC, with the trimmer that can be adjusted. Just a question of finding it on the board!

As with any equipment with high voltages floating around, it is imperative that you make any adjustments with the TV switched off unless you are confident (that's my get-out clause :) ) - and that the trimmer adjustment will be verysmall.

Llew
 

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spiney

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#10
Yes, but I'd like to point out, Artist has just paid somebody to - presumably - do an alignment? Using - presumably - proper test equipment. Now we're saying "try random fiddling"!

I can't see that it's actually the dry joint problem. Surely that would be intermittent according to temperature etc, whereas the problem sounded consistent! But, if so, can be v difficult to find, and then it's a soldering iron!

I'd say, do try a video rec output to tv channel retune, first, before doing anything else.
 
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#11
Yes, but I'd like to point out, Artist has just paid somebody to - presumably - do an alignment? Using - presumably - proper test equipment. Now we're saying "try random fiddling"!
You can call it what you like, Spiney, but it's a quick fix on these Sonys that often works. The trimmer used in this chassis can be suspect, replacing it with a 22pF fixed capacitor is a possibility.

I agree that it doesn't sound like a dry joint from the symptoms though.


Llew
 
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spiney

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#12
All fair enough, Llew, Artist says he wants to tweak, which is up to him of course, it's just he says it was working better!

"To tweak, or not to tweak: that is the question....

.... to tweak, perchance adjust ......

the thousand natural shocks the PCB is heir to;

.... and thus the native hue of PAL colour
is sicklied o'er with the pale cast of monochrome
with this regard their currents turn awry".

(with apologies to whoever wrote the original!).
 
A

Artist 2004

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#13
I love a good twiddle. My experience of twiddling in a long career of twiddling is that I have about a 50% chance of making things worse (approximates to Spiney's viewpoint) which is the same as a 50% chance of making things better (approximates to Llew's viewpoint).

I have a bit of a problem tuning a TV channel to my VHS recorder, I broke my remote about 8 years ago and a Sony replacement with hundreds of buttons and hidden compartments and sliding doors was expensive. So my TV channels have been stuck on BBC1 and 2, ITV and Channel 4 and one channel for my VHS recorder ever since I left England :D . That's why I'm using a SCART connection between it and the TV.

I've been trying switching my sat receiver between CVBS and RGB, and I'm getting flashes of B&W on CVBS but RGB is rock solid. I must read back and see what I can deduce from that.

Thanks for the diagram Llew, I'm 50% decided to live with it... if I take the plunge and whack that trimmer I'll post the results.

Spiney, rural TV repair men in Turkey NEVER have proper test kit! In fact no tradesmen EVER have the tools they need. I just made a 100 mile round trip to collect my extending ladder from storage so a local house painter can paint my house..... :-rofl2
 
Llew

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#14
Fine Artist, let us know if you need further help.

BTW my Bush portable TV is Turkish made, 10 years old and no problems so far, despite plenty of rough handling and extremes of kitchen temperatures. But then I don't suppose it was assembled by the horny hands of rural craftsmen :-rofl2

Llew
 
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#15
Yes, artist, that's what we'd expect, partially working on CBVS means the PAL decoder still has some difficulty locking in, but the repairer probably improved things a bit! The RGB way avoids using PAL, so of course it works fine! So, is there still an actual problem?

OK, I don't know what the repairer did, but he might have optimised the colour lock on broadcast tv properly, ie at centre of capture range. You don't want to make that worse. If determined to tweak, at least clearly mark the current setting with a felt tip, or something!

Here in good 'ole blighty, spare remotes are easily available, original and generic, eg from Grandata www.grandata.co.uk (huge range, not listed online). I'd have thought Turkey must have at least one distributor providing a similar service, who could ship you one from within the same country!

Can't you re-tune your video using the front panel controls?
 
A

Artist 2004

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#16
The only problem I've got is playback with the video recorder and DVD player because the o/p is fixed at CVBS.

Unfortunately the TV front panel doesn't have any tuning controls so I can't retune it to the video recorder.

On all the internet searches I've done for replacement remote controllers I've found many "compatable" types, e.g. channel selection, basic teletext etc, but when you look at the specifications, if they provide any, none have tuning functions. I'll have another try...

Now, my pocket PC has a program which emulates a programmable remote controller. It should be possible for someone to capture infra red signals as a file and send them to me on internet...... I must start a new thread on that one!

At the moment the problem is not great so I think I'll put off adjusting the trimmer and just live with it.
Thanks a lot everyone for your guidance and explanations, I really appreciate it.
 
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#17
Well, www.grandata.co.uk do manufacturer original remotes, and international postage, the cost might not be worth it, but at least you can ask via email at the website!
 
A

Artist 2004

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#18
spiney said:
Well, www.grandata.co.uk do manufacturer original remotes, and international postage, the cost might not be worth it, but at least you can ask via email at the website!
I'll give them a try - I'm sure some relative or friend can bring it out this summer looking for a free holiday in the sun!
 
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#19
Grandata shop is opp Wembley Stadium, easily reached. Give your friend the tv exact model number (!), all the stuff off the back and in the manual!
 
A

Artist 2004

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Two 80cm offset dishes.
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#20
spiney said:
Grandata shop is opp Wembley Stadium, easily reached. Give your friend the tv exact model number (!), all the stuff off the back and in the manual!
Thanks for that. Model number is easy, I've still got the manual, it's a UK machine so no problems with foreign model numbers and the remote also has its own number.
 
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