http://www.pinrepair.com/sys3/#cpu

Another interesting note is sometimes upon power on, the CPU board won't boot. Instead it will make strange squawking noices. If you've measured the +5 volts at the CPU board and found it to be in the 4.95 to 5.15 volt range, try a small test. While the game is on and squawking, change the +5 volt adjustment pot on the power supply (in either direction.) If the game now stops squawking and boots, measure the +5 volts. If it is in the 4.95 to 5.15 volt DC range, then leave it at that adjustment. If you have to repeat this procedure in the future to get the game to boot, suspect a problem on the CPU board with chip U11 and the two 1 mfd capacitor to the right and left of that chip at C20 and C21. Also check resistors R5 and R6 (originally 330k ohms, but was changed to to 680k in later CPU boards to be less sensitive to the watchdog circuit.) As a bit of history to this for example, on Cue Ball Wizard R5/R6 were 330k resistors and a 6116 RAM was at U3. By Wipeout resistors still R5/R6 were 330k but U3 RAM was a 6264. Then by Stargate R5/R6 changed to 680k ohms (and of course U3 was 6264 RAM.) But the base CPU board is the same with the only difference being these components.