Quoted from iluvak9:
I turned the game off and back on again, and found the game was not able to restart and it appears that the MPU flash test only gets through four or five flashes before it stops and the game freezes in the same state as it was in when it went crazy during the lamp diagnostic test.
Is it the 4th or 5th flash? I'm not familiar with the Weebly MPU, but for the original Bally 2518 (from http://techniek.flipperwinkel.nl/ballyss/rep/index2.htm#flash):
The Fakers Guide: no fourth flash means U10 (6821 PIA) is bad.
Techno Guide: The U9 CPU chip now tests the first 6821 PIA chip. There are two of these chips on the MPU board, which are identical and interchangable. The test for both is the same.
To determine if a PIA chip is good, the U9 CPU does the following:
- The CPU accesses, by means of input RS0, RS1, CS0, CS1 and CS2 each of the two full byte registers used to store the port initialization information. If does this, one register at a time. After it completes the first register, it repeats for the second. It goes through 256 tests similar to that used to check each byte in U7 (second flash). If each time the CPU writes a word into the register, it can read the same word back, it continues to test until completion.
- The CPU accesses, by means of input RS0, RS1, CS0, CS1 and CS2, each of two full byte registers used as data output registers when PA0 to PA7 and PB0 to PB7 are used as outputs. It does the same type of test on each register as described just above. Again if no faults are found, the test is continued until completion.
- The CPU then accesses, by means of input RS0, RS1, CS0, CS1 and CS2, the two ports CA2 and CB2. The port is initialized as an output. The port is then written into to see if it can store a "1" and then a "0".
- A total of 4 x 256 + 4 (=1028) test steps are required to test the PIA chip. However, there are internal buffer amplifiers used with the PB0 to PB7 output registers and CB2 port register which can not be tested by the CPU. Access is only to the register; if the buffer is open, it does not interfere with the registers ability to be written into and read from by the CPU. It is this uncertainity that reduces the accuracy of these test to 99.5%.
The Fakers Guide: no fifth flash means U11 (6821 PIA) is bad.
Techno Guide: Same test is performed on U11 as was performed on U10. See above.