Modifying the Bush STB CPU Clock

This is a relatively simple modification which will give around 30% speed increase in cpu processing, this is achived by changing the CPU clock from 48Mhz to 64Mhz syncronous with the main memory.

This modification relies on an assumption. This is that although the 7500FE is marked as a 56Mhz part, It is known that cirrus used parts capable of 64Mhz operation but stamped them 56Mhz. This was because Cirrus were unsure of their new process (newer parts have the "maverik" logo on them) and erred on the side of caution (a good thing to do).

Start by locating the 64Mhz memory crystal in the South West of the board, it is labeled X6.
Unmodified region around X6

Remove the zero ohm link R80
The R80 link removed

Attach a 4.7Kiloohm resistor between the indicated pads. Actualy any resistor between 4.7K and 10K will do, its just acting as a pull up.
Indication of the pads to connect

Congratulations! your bush STB main CPU now runs syncronously at 64Mhz with your memory.


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