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ZX81 1981 "ISS 3" Motherboard??

dreamscapedreamscape
edited August 2014 in Hardware
I took my ZX81 apart today never seen inside one before so had a look and saw a mainboard I've never seen here or online before?

IMG_20140818_160323.jpg

IMG_20140818_160449.jpg

IMG_20140818_160628.jpg

IMG_20140818_160720.jpg

I'm guessing this is a first revision board? it's got 1981 stamped on the board?

Any other info on this board? :???:
Post edited by dreamscape on

Comments

  • balfordbalford
    edited August 2014
    Nope, there were two revisions of the ZX81 motherboard:

    - Issue 1 (hand layout, most common, green solder mask)
    - Issue 3, your board (CAD layout, sold from approx. 1983 onwards, may have green or red solder mask)

    Issue 2 boards have not been discovered in the wild or documented, although there is a USA Issue 1 which has the same basic layout as the UK Issue 1 but with CAD laid out traces.

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • dreamscapedreamscape
    edited August 2014
    Thank you, very informative :)
  • balfordbalford
    edited August 2014
    No problem :) Looking at the above pictures again I see a date code of 8317 on the ULA so that tallies with the above.

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • dreamscapedreamscape
    edited August 2014
    Fantastic, great to know which board i have. What were the changes made between the revisions out of curiosity or was it purely layout?
  • balfordbalford
    edited August 2014
    Issue 3 boards tend to have the 2C210E ULA, which has a better (but still not great) chance of working with more modern TV's.

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • dreamscapedreamscape
    edited August 2014
    Oh that's good as i was hoping to avoid any modification to the machine such as the composite mod.

    Thanks for you're help very helpful indeed!
  • moggymoggy
    edited August 2014
    It'll work with the older CRT colour TVs but not so well with the modern LCD/plasma types as they expect a PAL signal that's no so out of whack as the signal that comes out of a zeddy.
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