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Improving RF-modulator output

maten149maten149
edited September 2005 in Sinclair Miscellaneous
My old 48k is working perfectly, except for
the RF-modulator output giving unclear colors, moire type effects - generally being a bit
bad and drifting with temp.

Can this be related to old CAP's being dried
up for instance? Has anyone any ideas to what
kind of service replacement I can make to improve and refresh the stability of the RF output?

I'm quite used to soldering and not afraid to attack my old speccy with a soldering iron.. :)
Post edited by maten149 on

Comments

  • absorbentgnomeabsorbentgnome
    edited August 2005
    Yeah the capacitors do tend to dry up, allowing noise and voltage drift to become present on the various supply rails. New electrolytic caps should clear it up, but there was always a fair bit of 'computer noise' on the display anyway. You can identify duff caps with localised heat, but 'cos they're so old anyway you might as well replace the lot.
  • maten149maten149
    edited August 2005
    It is all very improved now, I found
    two varicap's next to the ULA and started
    turning them ever so lightly; lo and behold, the image stabilised :D

    However, whether a design flaw or not, red text on top of green background is difficult to make out. Even though it is sharp, red color simply won't show in thin lines on the green background...

    /M
  • absorbentgnomeabsorbentgnome
    edited August 2005
    On 2005-08-12 23:58, maten149 wrote:
    It is all very improved now, I found
    two varicap's next to the ULA and started
    turning them ever so lightly; lo and behold, the image stabilised :D

    However, whether a design flaw or not, red text on top of green background is difficult to make out. Even though it is sharp, red color simply won't show in thin lines on the green background...

    /M

    Lol, a much simpler solution!
  • SpecboySpecboy
    edited September 2005
    I had a similar problem and it turned out to be the actual TV set I was using. Originally I plugged my Speccy into my TV in my living room, tuned it in and found that I was getting strange patterns on screen and intermittent loss of colour etc. Tried finetuning but couldn't get it any better. So I tried my Commodore 64 on the same TV got a cracking clear picture but only in black and white. So then tried both machines on an old Ferguson TV which I have in my bedroom. Perfect picture. Spoke to a TV engineer I know and he said part of the problem is Channel 5 which broadcasts on CH36 same as your spectrum and the other part is down to some newer TV's with digital tuners don't like old equipment such as Spectrums, old videos etc.

    Fortunately in my case I didn't have to take my beloved speccy to bits



    [ This Message was edited by: Specboy on 2005-09-15 19:02 ]
  • TimppaTimppa
    edited September 2005
    You can easily mod Spectrum to use S-Video: (much improved picture)
    1. Open modulator 2. Solder out resistor connected to tv-socket. 3. Put wire through modulators empty hole and solder it to socket. 4. Solder other end of wire to underside edge connector pin 15 (see: http://www.breezer.demon.co.uk/spec/tech/zx-edge-connectors.txt FBAS is video signal).

    Now you can connect Speccy to TV's S-Video socket. Note: on later models (+3,+2a) pin 15 was replaced with ROM2OE so this does not work, but then you can build Scart lead instead.

    Timppa
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