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Tuning issue 48K

crazylarrycrazylarry
edited October 2009 in Hardware
Hi. I have just bought a 48K rubber key version and am having trouble tuning it in. I have tried two newish CRT televisions but get the same picture.
I can just about see the Sinclair Research logo, but there are lots of white lines on the left hand side of the screen. I provide a picture here (excuse the bad quality):

DSC00067-1.jpg

Would the composite video mod be recommended?

Cheers

Matt
Post edited by crazylarry on

Comments

  • Mad FritzMad Fritz
    edited October 2009
    Welcome to WOS and: yes, I allways recommend the composite mod, even if the TV-picture has better "quality" than in your case.

    BR
  • crazylarrycrazylarry
    edited October 2009
    Hi BR. Thanks for the welcome! So you would recommend the video mod even though it might not fix the problem I am seeing?

    Cheers.
  • Mad FritzMad Fritz
    edited October 2009
    Yes.
    If it works with the composite mod (which is not a big deal, just solder a cinch cable on modulator input and ground, a capacitor as mentioned in the proper mod is a plus but not a must just for testing purpose) then you at least know the modulator causes the problems.
    If not, then the experts here can give you further advise.

    Best Regards

    Mad Fritz
  • crazylarrycrazylarry
    edited October 2009
    It worked! First time I have ever soldered something in my life! Great stuff.
    However, whenever anything in colour is on the screen it starts rolling. Has anyone seen this problem? Many thanks.
  • rokoroko
    edited October 2009
    Mad Fritz wrote: »
    Yes.
    If it works with the composite mod (which is not a big deal, just solder a cinch cable on modulator input and ground, a capacitor as mentioned in the proper mod is a plus but not a must just for testing purpose) then you at least know the modulator causes the problems.
    If not, then the experts here can give you further advise.
    Where a low impedance common collector stage is already present in the Spectrum, it is possible to mix RF and Composite onto the 'TV' connector: Insert a 10 pF capacitor in the RF signal directly behind the Cinch connector, then simply add the Composite signal over a 100 - 200 Ohm resistor direct to this connector. Then Video as well as RF can be taken from the same 'TV' connector. Works fine for me.
  • crazylarrycrazylarry
    edited October 2009
    roko wrote: »
    Where a low impedance common collector stage is already present in the Spectrum, it is possible to mix RF and Composite onto the 'TV' connector: Insert a 10 pF capacitor in the RF signal directly behind the Cinch connector, then simply add the Composite signal over a 100 - 200 Ohm resistor direct to this connector. Then Video as well as RF can be taken from the same 'TV' connector. Works fine for me.

    I'm not exactly clear as to what this all means! But I would appreciate any help regarding the rolling screen problem. Many thanks.
  • rokoroko
    edited October 2009
    Could it be that your Spectrum is an Issue 2?
  • Mad FritzMad Fritz
    edited October 2009
    Did you apply the "proper" mod using an electrolyte capacitor or just a straight connection from modulator input?
  • crazylarrycrazylarry
    edited October 2009
    Hi guys. It's an issue 4A. I only applied the straight connection from the modulator input. Cheers.
  • crazylarrycrazylarry
    edited October 2009
    The rolling screen issue isn't as frequent now. But when I set the screen to flash, or when it loads a game the screen jumps. If I stop loading or stop the flashing, the screen returns to normal. Cheers.
  • HerculesHercules
    edited October 2009
    You mention the composite mod has helped reduce the problem.

    Things to check:-

    We can now rule out RF tuning here as your going composite via phono cables to phono input on the television, so...

    I would put it down to RF interferance being picked from the modulator itself. Maybe try someway of screening the modulator from picking up internal noise that may effect the picture.

    After completing the composite mod, the second cause could be a cheap phono cable (make sure you use a well screened phono cable to connect the Spectrum to the television) to minimise interference).
  • rokoroko
    edited October 2009
    A mod with two capacitors, reducing interfering noise coming from within the Spectrum: http://user.tninet.se/~vjz762w/rebuild.html
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