NESRGB Grey Background Fault

Recently I have become aware of a fault in all NESRGB boards shipped between 15th and 23rd of January 2014.

The latest batch of NESRGB boards have a new RAM chip, the AS7C3256A-12TCN. The previous boards used a CY7C1399BN-12ZXC CY7C1399BN-15ZXI. These two parts are functional equivalents, however, the use of AS7C3256A-12TCN introduced a subtle bug in the program. The background colour value is not updated in some games.

Correct operation:

background_fault_blue.jpg (43850 bytes)

Faulty board operation. The background is grey in many games:

background_fault_grey.jpg (56181 bytes)

Solution #1: Replace the RAM Chip

By removing the AS7C3256A-12TCN and soldering a CY7C1399BN-15ZXI in its place, correct operation will be restored.

board_ram.jpg (70772 bytes) ram_chip.jpg (28659 bytes)

desolder_ram_2.jpg (40899 bytes)

This solution is only suitable if you are skilled at SMT soldering. If you have never soldered SMT parts before please do not attempt this procedure.

To remove the old RAM chip:

To solder on the new RAM (CY7C1399BN-15ZXI) chip:

Solution #2: Reprogram the PLD

See the software page for programming details.