Mains interference?

Discussion in 'Plasma TVs Forum' started by TimSoane, Oct 6, 2002.

  1. TimSoane

    TimSoane
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    I have small bands of distortion across my TH42PW4B. It seems to be associated with the mains lead. Take off the ferrite core and it gets much worse. With the core back on, it is better and in moving pictures hardly notices, but it shouldn't be there. I'm using an S-video connector from a Bose 1-2-3 and Sky+ receiver. Any suggestions. Plugging in the Bose supplied video cable also helps, but not if near a mains cable.
     
  2. ShaggyDragon

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    Hi there, I can't help your problem except to say that I have exactly the same problem on the S-Video input from Sky + to my Toshiba 42WP27 (Panasonic 5 series). The interference can be described as stripes of increased brightness moving across the picture. This is especially evident on the menus and when you change channel.

    This is my 2nd Toshiba as I thought the 1st was faulty due to this problem. This panel has exactly the same problem. I also get this problem when using the component output from an X-Box console. Dark colour images experience a similar problem with diagonal interference lines moving from right to left on the picture.

    I have experimented by moving the panels onto the dining room table with the power and signal cables as far apart from each other as possible. I also switched off virtually all items in the house including wireless hub - just in case it was causing the problem. None of this made any improvement.

    Not sure what to try now. Any help will be really appreciated.

    Andy.
     
  3. derekrcross

    derekrcross
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    sorry to hear your having trouble have you checked out the electrics for loose connections that you have a good earth and are you sure your not getting interference from lighting have seen this before caused by dimmer switch worth a look
    good luck
     
  4. ShaggyDragon

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    Thanks for the suggestions, I've just tried plugging it into an APC 1400 UPS. That provides an excellent smooth power source and a good earth. Also, I tried switching off all items in the house - including lights. Still the same problem.

    I'm pretty sure that the output from my Sky+ SVideo socket is fine, also I tried the component output from my X-Box in the shop on another Toshiba plasma - it too was perfect.

    Running out of ideas here chaps.. Can anyone help?

    Andy.
     
  5. TimSoane

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    Nice to hear that I am not alone. I have had the following reply from Panasonic. I have yet to try all of them. Some I had already tried... The one I am stuck on is using the original plug, because I cut it off the lead to fit the monitor...

    Tim

    QUOTE

    In response, I would explain that In order to provide you with a full response, I have taken the opportunity to consult with our resident technical support advisors. They have explained that THE MAINS LEAD IS FULLY MOULDED AND SHOULD BE LEFT AS SUCH. SOME CUSTOMERS REMOVE THIS PLUG FOR EXTENSION PURPOSES. ENSURE THE MAINS LEAD IS NOT MODIFIED.

    THE SOURCE EQUIPMENT MAY BE TOO FAR FROM THE UNIT. TRY REDUCING THE LENGTH OF WIRING BY BRING THE UNITS CLOSER. THIS WILL MINIMISE INTERFERENCE IF BEING PICKED UP ON THE CABLE.

    THE FERRITE CORES ARE MAINLY USED FOR THE PC CONNECTION INPUTS (SEE PC CONNECTION DIAGRAM IN INST BOOK) AND SHOULD NOT BE NEEDED FOR NORMAL VIDEO USE.

    THE FACT THAT THE SIGNALS IMPROVE WITH THERE USE INDICATE THAT SOME FORM OF RADIATED INTERFENCE IS BEING PICKED UP.

    TRY SWITCHING OFF SOURCE EQUIPMENT FROM THE MAINS TO ELIMINATE ANY FORM OF EMISSION FROM THESE UNITS.

    ALSO TRY USING A DOUBLE SCREENED CONNECTION LEADS. THIS SUGGESTION WAS MADE BEFORE BUT NO RESPONSE WAS MADE.

    WHICH INPUTS ARE BEING USED ON THE PLASMA PANELS FOR CONNECTION?

    FINALLY, ENSURE THE TERMINAL PCB IS CORRECTLY INSERTED AND THE 4 SECURING SCREWS ARE WELL TIGHTENED. TRY REFITTING THE BOARD.

    IF THIS FAILS TO RESOLVE THE ISSUE, THEN YOU SHOULD ARRANGE FOR YOUR DEALER TO VISIT AND ASSESS THE SITUATION.

    I trust that the above information will be of assistance to you. However, of course, if you should have any further queries, please do not hesitate to contact us on 08705 357357 or [email protected] and we will endeavour to assist.

    UNQUOTE
     
  6. symanski

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    This is a massive subject, so I'll only be able to cover a tiny amount in this post. There's many many books written on the subject, but I'll cover the two parts here.

    Ferrites.
    These are filters that you put directly on to the signal or power lines. The material acts as a load to the signals carried, but only over a certain frequency range. Typically, 10MHz to 600MHz but this does vary. For reference, TV & Video goes up to 6MHz.

    Ground Loops.
    A ground loop is exactly what it sounds like, you've got a loop around your equipment all connected to ground. The problem arrises when you don't have perfect grounds, and noise is present on the loop, probably from one item. I have seen this in home-ciinema systems appreaing as streaks down the TV.

    This is what I believe is your problem, based upon two facts. First, disconnecting one item helped, and secondly, the filtering by the ferrittes also helped.

    Now you've identified the problem, how do you fix it? You've got to identify the real source. Start with stripping your system down. Go through all your sources and only put it in in isolation. Then start adding to your system until you find the worst offender.

    Adding more ferrites to your signal cables can also help. But improving the grounding can too. It's a difficult problem to completely eliminate.

    All the best,

    Dr John Sim.
     
  7. TimSoane

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    Thank you John. Very helpful. I am encouraged to try a few more experiments.
     
  8. ijwoo1

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    SNAP. I have a PW5 and the TUPTA600. I'm beginning to wonder if this is contributing to the "flicker" I have been describing in other threads.

    My bands of varying brightness roll vertically, they appear to be present on all video sources. RGB, Svid and component via the tuner, including the internal tuner output itself. I can live with it because its barely noticeable at normal viewing distance, but its certainly there as you describe. Particularly on Sky menus and in between channel changes.

    I have actually screened the mains cable just in case the proximity of it to the main video cable was causing the problem. I used heatshrinkable shield around the external insulating sleeve of the original cable. The shield is earthed. This has made no difference at all though.
     
  9. Paul D

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    I checked my PW5B to check for this interference, and there is zero moving banding etc.

    I know this will be no comfort to you, but though it would give you extra info if you call out Panasonic and they try to say it is normal etc.

    I'm sure i read something on AVS forums about the tuner box being the source of very bad banding and flickering, but since yours is subtle maybe it's something different.
     
  10. ShaggyDragon

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    I'm very confused as to why some of us are experiencing some pretty serious interference on these Panasonic/Toshiba devices when others seem to have perfect pictures. I have now eliminated all possible sources of RF that I can:

    1. I have nothing switched on in the house except the XBox and plasma.
    2. The Xbox has been tested through S-Video and component and the plasma has the purest mains supply I can get (APC 1400).
    3. The screen has been moved into a room far away from speakers and other electrical devices.
    4. The mains cable and signal cables are positioned as far away from each other as possible.

    The banding is still present. This is the 2nd plasma to exhibit these problems. What can I do?
     
  11. MysT

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    Hi all,

    I'm not sure if this is what's being described as banding but I have observed what looks like rain in the background which is most prominent on a freeze frame of a grey image. I can also see interference in the form of dark flecks moving from right to left horizontally every 1/3 of a screen in height. I'm almost convinced this is being caused / picked up by SKY+ or my JS box or VGA cable, more testing will be required, I do not see any problems watching a DVD via component or using a PC connected to the VGA input so I'm fairly sure it's not the plasma itself, I tried ferrite cores and they made no difference what-so-ever.

    I did get what's best described as banding using s-video out from SKY+ both on the plasma and when using s-video in on my PC's graphics card, I put that down to the SKY+ box itself and upgraded to using RGB.

    Has anyone been able to completely eliminate their SKY+ box as the problem?
    How is everyone's SKY+ box hooked up? anyone using a JS convertor to VGA?

    Cheers,
    Chris.
     
  12. symanski

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    ShaggyDragon,
    have you disconnected everything to the screen first? Banding is not necessarily because some other device in the house is coupling on to your signal leads, but rather conducted emissions from the devices already connected. Hence, you my have a noisly ground connection, in a loop, and causing the banding effects. This is something that I have observed in the past with CRT TVs. My advice is to strip down your system so that you've only got one source connected to your screen and work from there. To do anything else at this stage is folly.

    MysT,
    How good is the SCART lead going in to the Plasma VGA unit? It's not something that's been reported before. Feel free to email me.

    All the best,

    Dr John Sim.
     
  13. ShaggyDragon

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    That was the first thing I tried. If you imagine a plasma in an empty room connected to mains. The Xbox is connected to it by either SVideo or Component (not both at the same time). The cables have been run as far apart from one another as possible. At one stage I plugged both units into an APC 1400 UPS to try to smooth the power. It was still doing the same thing.

    As this is the 2nd screen that exhibits this problem, could Toshiba have a faulty batch of 42WP27s ?

    The X-Box was tested on a plasma screen in the demo room of the plasma supplier. This was with all of the demo equipment in the shop switched on. Surely this is would cause far more interference than I get in a house with absolutely no electrical items switched on?

    Best regards, Andy.
     
  14. symanski

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    Try a DVD player rather than an XBox.

    As for interference, you've to two types. Conducted and radiated. Radiated is like radio transmissions which couple on to signal lines. Conducted is directly via an lead from one device to another. So you might not have a radiated emission problem, but you could still have it via a lead between devices.

    If you go right back to a single source, and you've still got the problem (and with ferrites on the cable - as many as you can find), then there's not much else you can do.

    All the best,

    John.
     
  15. clam

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    Well you me to the list of people suffering "banding". I have a 42"PW5 and I get this problem as described by all above.

    As with others here it does seem to be limited to the S-Video connection which I use for Sky+. I have to say that I don't notice it when watching actual programs, it only shows itself on the menus's and between channel changes where the blue background is the only thing visable.

    It would seem that it's a Sky+ S-Video problem, but there are a couple of exceptions.....

    ijwoo1 seems to have it on all connections via the tuner box

    fulabeer - do you have Sky+ connected with S-Video ??

    MysT - I think your on the right track, what we need is someone who gets banding on the S-Video connection with Sky+ but has a JS box to tell us if it happens on that too....

    failing that, Dr Sim could you lend out one of your magic boxes for us to test ??
     
  16. ijwoo1

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    I did some more 'viewing' of the phenomenon.

    I just want to differentiate between Flicker and Banding. Whether they are related I do not know, but the two are distinctly recognisable.

    The banding causes a sort of flicker but I also get flickering without banding, if that makes sense.

    I have a DBS20 early panasonic Digibox which is connected to an RGB/Svid convertor which then feeds to the Tuner. Banding is exactly as every one describes on Sky. What I can't make out though is if the banding is still there on the normal picture and not just between channel changes, its certainly less noticeable on the normal picture. Perhaps because its masked by flicker !

    Anyway flicker is present on all inputs, this is different to the banding I get with Sky. However, I do also notice banding when viewing ITV via the Tuner.

    From all this I conclude that :

    The "Banding" is Sky digibox or RGB/SVid convertor specific and not just SVid. Other Svid sources do not show banding but DO flicker.

    That the "Banding" on ITV is a coincidence and just RF interference on the aerial feed. Other tuner RF channels show NO evidence of banding.

    The "Flicker" is present on all sources regardless of signal type and occurs with and without the presence of "Banding"

    This all sounds very negative, so to put it in perspective; I wouldn't swap it for CRT :)
     
  17. Paul D

    Paul D
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    I use the SKY+ box via the "Ferrit" screened Syncblaster cable.
    (RGB scart to 15 pin VGA input etc)
     
  18. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Moving bands are almost definately hum bars as John has said. In my experience this is caused for the reasons John has said also. In you r home the thing I found to most often cause this phenomenom is the aerial system. Disconnect the aerial form your sources and see what happens.

    It might also be an idea to get an electrician to check the earth bonding of the consumer unit/s in your home. It wouldn't be the first time that this has been the source of such a problem.

    Gordon
     
  19. ShaggyDragon

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    Yes it is particularly evident with the SVideo output from Sky+. Yesterday I decided to make an Scart to RBG cable and give that a try. WOW - what a difference. The picture is clean and stable, with no banding interferance at all.

    Assuming that JS's Scart to Component converter will produce a similar (obviously not identical) picture to this, I'm going to send in an order. Also, RGB doesn't allow "Just" modes, so watching the 4:3 material that is prevalent on Sky is a bit of a pain in Zoom or 16:9. The component input allows the "Just" mode.

    All I need to do now is find a convenient method to switch 3 component sources, without the need for a £1799 purchase of an amp.

    Andy.
     
  20. symanski

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    The good news is that component switching amplifiers are becoming more available. I read in one of the magazines of one which was at the lower end of the market which has this.

    As for banding, I think trying Gordon's suggestion would also help. Everything else I've already stated in this thread, and would only be repeating. Adding extra ferrites might be a good idea as Sky and Plasma screen are essentially very fast embedded computers, and these can be noisy (electrically speaking).

    All the best,

    Dr John Sim.
     
  21. MysT

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    Hi,

    Just an update, most of the problems I was experiencing went away when I changed my scart lead (thanks for the advice John)for a Supra AV6 cable, 72 quid! ouch but well worth it, next will be the VGA cable for a VanDamme one and I hope that will do the trick with the remaining interference.

    Cheers everyone,
    Chris.
     
  22. SimonA

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    You can add me to the list of people seeing the banding on S-video from my Sky+ box.
    I have a scart RGB going through a JS Box into the VGA input and that signal is completely clean.
    I also use the S-Video connection from the Sky+ box, (purely because of the greater aspect ratios available on the AV input on the Panny 5, used for those channels that don't transmit 16X9)
    and get the banding on the blue background when changing channels.
    Looks like I'll have to fiddle with connections as well.

    Are we sure that the problem is not with the S-video ouput from the sky+ box? Is anyone using this connection to a panny 5 and getting a clean signal?

    Cheers

    Simon
     
  23. ShaggyDragon

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    I'm glad that many of us are experiencing the same problem with Sky+ and SVideo. I just wish there was a solution.
     
  24. symanski

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    One person did buy an S-Video converter and then upgraded to Sky +. While he could use the S-Video from Sky +, the converted S-Video was better as it was free of bands etc. Picture quality was, therefore, better.

    Typically, if you have Sky + I would say to stay with the S-Video output it has. However, there does seem to be the case where you can get better results if you don't!

    All the best,

    Dr John Sim.
     

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