ZX81 Dark Screen

Frequently Asked Questions about the Sinclair ZX81
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RWAP
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ZX81 Dark Screen

Post by RWAP » Mon Oct 31, 2011 10:41 am

Some early ULAs used in the Sinclair ZX81 lacked what is known as the 'back-porch latch'. This circuit proves essential when you need to connect a ZX81 to a modern LCD / LED television set, or even when trying to use it with a colour TV.

The issue presents itself as a very dark grey screen when you switch on the ZX81, which is not good when you are using black text - in fact on most TVs, it is illegible.

There have been several do-it-yourself circuits on the internet, but you can now purchase the ZXVid module which replaces the innards of the TV modulator used on the ZX81, providing both a fix for the back-porch latch and also providing composite video out for a strong stable picture.

See viewtopic.php?t=628 for more details

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