Williams D8224 (Type 2) sound board on-board RAM jumpering Guide.
The D8224 sound board uses the Motorola 6808 CPU chip. Since the Motorola 6802 CPU chip is 100% compatible it can also be used as a drop in replacement. So, what is the difference between a 6808 and a 6802? The 6802 has on-board RAM in addition to the functions provided by the 6808 though it is not enabled by default.
This can be very handy when repairing these boards if the 6810 RAM chip has failed. Some, but not all 6810 failures can be repaired by fitting a 6802 and enabling the on-chip RAM. If the faulty 6810 is affecting the buses then you will also have to remove the 6810 from the board. I test the 6810 RAMs in circuit using a Fluke 9010A troubleshooter with a 6808/6802 POD.
Fortunately Williams thought of this when designing the Sound boards and so by removing jumper W14 the 6802's on-board will be enabled (this pulls the RAM Enable signal, pin 36 of the 6802 to a high state), however, unlike the other jumpers on the sound board it is not the zero ohm resistor type, but rather a track on the board.
The photo shows the jumper cut position under R30 highlighted in red.
To enable the internal RAM of the 6802 CPU perform the following actions:
Remove the 4K7 resistor at R30.
Cut the track under R30 as shown above
Refit R30 in the original position.
To disable the internal RAM of the 6802 CPU perform the following actions:
Remove the 4K7 resistor at R30.
Fit W14 (a zero ohm resistor) offset to the original position of R30 as shown in the photo.
