The MOS 8701 chip creates the clocks used by the Commodore 128 and later Commodore 64 machines. If your display is sized completely wrongly, or if you have a "no signal" error on your TV, this could be at fault. It is unlikely to be the cause of a displayed black screen which the TV (which is very different to a blank screen which the TV can't display).
Our 8701 chips are tested in our Commodore 128 to check all clocks are working correctly. When replacing an 8701 chip (which is easy to do as they're usually socketed) please be aware that a bad connection caused by a dirty socket may cause the Commodore 128 to enter the monitor on start-up. If this happens, a clean of the socket will usually fix it.
