Battery Corrosion.
One BIG problem with system11 games are the batteries. The CPU board has mounted at the top center a 3-AA battery pack. This keeps audits, adjustments and high scores in memory when the game is powered off. But if the batteries are neglected and grow old, they can leak their corrosive fluids on the CPU board, ruining the board. If this has happened, there are a number of components directly below the battery holder than are often affected. For this reason, and to aid in the replacement of PIA chips for other reasons, I will list where these large 40 pin PIA chips connect. This way you can "buzz out" the chip legs and make sure they still connect to their intended components (because often battery corrosion can eat these traces). If even a single trace to one of the PIA or support chips is broken, this can cause the entire CPU board to not "boot".
PIA and Support Chip Connections.
Here's a list of all the PIAs connections (except for the sys11-sys11b sound PIA).
PIA U41 (display)
pin 1 = gnd
pin 2 (pa0) = src5 pin 2, j22 pin 11
pin 3 (pa1) = src5 pin 3, j22 pin 12
pin 4 (pa2) = src5 pin 4, j22 pin 13
pin 5 (pa3) = src5 pin 5, j22 pin 14
pin 6 (pa4) = src5 pin 6, j22 pin 15
pin 7 (pa5) = src5 pin 7, j22 pin 16
pin 8 (pa6) = src5 pin 8, j22 pin 17
pin 9 (pa7) = src5 pin 9, j22 pin 18
pin 10 (pb0) = src2 pin 2, j22 pin 19
pin 11 (pb1) = src2 pin 3, j22 pin 20
pin 12 (pb2) = src2 pin 4, j22 pin 21
pin 13 (pb3) = src2 pin 5, j22 pin 22
pin 14 (pb4) = src2 pin 6, j22 pin 23
pin 15 (pb5) = src2 pin 7, j22 pin 24
pin 16 (pb6) = src2 pin 8, j22 pin 25
pin 17 (pb7) = src2 pin 9, j22 pin 26
pin 18 (cb1) = src1 pin 2, j21 pin 11
pin 19 (cb2) = u49 pin 5, sr19 pin 7
pin 20 = +5
pin 21 (r/w) = pin 21 on all PIAs, j21 pin 17, u36 pin 1, u13 pin 18, u16 pin 1
pin 22 (cs0) = pin 22 on all PIAs
pin 23 (cs2) = u37 pin 12
pin 24 (cs1) = pin 24 on all PIAs (a13 address bus), u14 pin 6
pin 25 (E) = pin 25 on all PIAs, u32 pin 10, u35 pin 1, u35 pin 3, u32 pin 13, u29 pin 10, u11 pin 18, j21 pin 19
pin 26 (d7) = pin 26 on all PIAs, u16 pin 9, u28 pin 8, u25 pin 17, u26 pin 19, u27 pin 19
pin 27 (d6) = pin 27 on all PIAs, u16 pin 8, u28 pin 13, u25 pin 16, u26 pin 18, u27 pin 18
pin 28 (d5) = pin 28 on all PIAs, u16 pin 7, u28 pin 14, u25 pin 15, u26 pin 17, u27 pin 17
pin 29 (d4) = pin 29 on all PIAs, u16 pin 6, u28 pin 7, u25 pin 14, u26 pin 16, u27 pin 16
pin 30 (d3) = pin 30 on all PIAs, u16 pin 5, u28 pin 17, u25 pin 13, u26 pin 15, u27 pin 15
pin 31 (d2) = pin 31 on all PIAs, u16 pin 4, u28 pin 4, u25 pin 11, u26 pin 13, u27 pin 13
pin 32 (d1) = pin 32 on all PIAs, u16 pin 3, u28 pin 18, u25 pin 10, u26 pin 12, u27 pin 12
pin 33 (d0) = pin 33 on all PIAs, u16 pin 2, u28 pin 3, u25 pin 9, u26 pin 11, u27 pin 11
pin 34 (reset) = pin 34 on all PIAs, u15 pin 40, u43 pin 4, sr19 pin 3, q39, r69
pin 35 (rs1) = pin 35 on all PIAs (a1), u25 pin 9, u26 pin 9, u27 pin 9, u11 pin 16
pin 36 (rs0) = pin 36 on all PIAs (a0), u25 pin 10, u26 pin 10, u27 pin 10, u11 pin 14
pin 37/38 (irq) = pins 37/38 on all PIAs, r70 (rt leg), u32 pin 1
pin 39 (ca2) = u49 pin 3, sr19 pin 4
pin 40 (ca1) = src1 pin 5, j21 pin 15
PIA U42 (display)
pin 1 = gnd
pin 2 (pa0) = src4 pin 2, j22 pin 3
pin 3 (pa1) = src4 pin 3, j22 pin 4
pin 4 (pa2) = src4 pin 4, j22 pin 5
pin 5 (pa3) = src4 pin 5, j22 pin 6
pin 6 (pa4) = src4 pin 6, j22 pin 7
pin 7 (pa5) = src4 pin 7, j22 pin 8
pin 8 (pa6) = src4 pin 8, j22 pin 9
pin 9 (pa7) = src4 pin 9, j22 pin 10
pin 10 (pb0) = src3 pin 2, j21 pin 3
pin 11 (pb1) = src3 pin 3, j21 pin 4
pin 12 (pb2) = src3 pin 4, j21 pin 5
pin 13 (pb3) = src3 pin 5, j21 pin 6
pin 14 (pb4) = src3 pin 6, j21 pin 7
pin 15 (pb5) = src3 pin 7, j21 pin 8
pin 16 (pb6) = src3 pin 8, j21 pin 9
pin 17 (pb7) = src3 pin 9, j21 pin 10
pin 18 (cb1) = src1 pin 3, j21 pin 12
pin 19 (cb2) = src1 pin 4, j21 pin 13
pin 20 = +5
pin 21 (r/w) = pin 21 on all PIAs, j21 pin 17, u36 pin 1, u13 pin 18, u16 pin 1
pin 22 (cs0) = pin 22 on all PIAs
pin 23 (cs2) = u37 pin 10
pin 24 (cs1) = pin 24 on all PIAs (a13 address bus), u14 pin 6
pin 25 (E) = pin 25 on all PIAs, u32 pin 10, u35 pin 1, u35 pin 3, u32 pin 13, u29 pin 10, u11 pin 18, j21 pin 19
pin 26 (d7) = pin 26 on all PIAs, u16 pin 9, u28 pin 8, u25 pin 17, u26 pin 19, u27 pin 19
pin 27 (d6) = pin 27 on all PIAs, u16 pin 8, u28 pin 13, u25 pin 16, u26 pin 18, u27 pin 18
pin 28 (d5) = pin 28 on all PIAs, u16 pin 7, u28 pin 14, u25 pin 15, u26 pin 17, u27 pin 17
pin 29 (d4) = pin 29 on all PIAs, u16 pin 6, u28 pin 7, u25 pin 14, u26 pin 16, u27 pin 16
pin 30 (d3) = pin 30 on all PIAs, u16 pin 5, u28 pin 17, u25 pin 13, u26 pin 15, u27 pin 15
pin 31 (d2) = pin 31 on all PIAs, u16 pin 4, u28 pin 4, u25 pin 11, u26 pin 13, u27 pin 13
pin 32 (d1) = pin 32 on all PIAs, u16 pin 3, u28 pin 18, u25 pin 10, u26 pin 12, u27 pin 12
pin 33 (d0) = pin 33 on all PIAs, u16 pin 2, u28 pin 3, u25 pin 9, u26 pin 11, u27 pin 11
pin 34 (reset) = pin 34 on all PIAs, u15 pin 40, u43 pin 4, sr19 pin 3, q39 (top leg), r69 (rt leg)
pin 35 (rs1) = pin 35 on all PIAs (a1), u25 pin 9, u26 pin 9, u27 pin 9, u11 pin 16
pin 36 (rs0) = pin 36 on all PIAs (a0), u25 pin 10, u26 pin 10, u27 pin 10, u11 pin 14
pin 37/38 (irq) = pins 37/38 on all PIAs, r70 (rt leg), u32 pin 1
pin 39 (ca2) = src1 pin 8, j21 pin 18
pin 40 (ca1) = src1 pin 6, j21 pin 16
PIA U38 (switch matrix)
pin 1 = gnd
pin 2 (pa0) = u30 pin 4
pin 3 (pa1) = u30 pin 3
pin 4 (pa2) = u30 pin 10
pin 5 (pa3) = u30 pin 11
pin 6 (pa4) = u39 pin 4
pin 7 (pa5) = u39 pin 3
pin 8 (pa6) = u39 pin 10
pin 9 (pa7) = u39 pin 11
pin 10 (pb0) = u40 pin 2
pin 11 (pb1) = u40 pin 17
pin 12 (pb2) = u40 pin 4
pin 13 (pb3) = u40 pin 15
pin 14 (pb4) = u40 pin 6
pin 15 (pb5) = u40 pin 13
pin 16 (pb6) = u40 pin 8
pin 17 (pb7) = u40 pin 11
pin 18 (cb1) = gnd
pin 19 (cb2) = u49 pin 11, sr19 pin 8
pin 20 = +5
pin 21 (r/w) = pin 21 on all PIAs, j21 pin 17, u36 pin 1, u13 pin 18, u16 pin 1
pin 22 (cs0) = pin 22 on all PIAs
pin 23 (cs2) = u37 pin 11
pin 24 (cs1) = pin 24 on all PIAs (a13 address bus), u14 pin 6
pin 25 (E) = pin 25 on all PIAs, u32 pin 10, u35 pin 1, u35 pin 3, u32 pin 13, u29 pin 10, u11 pin 18, j21 pin 19
pin 26 (d7) = pin 26 on all PIAs, u16 pin 9, u28 pin 8, u25 pin 17, u26 pin 19, u27 pin 19
pin 27 (d6) = pin 27 on all PIAs, u16 pin 8, u28 pin 13, u25 pin 16, u26 pin 18, u27 pin 18
pin 28 (d5) = pin 28 on all PIAs, u16 pin 7, u28 pin 14, u25 pin 15, u26 pin 17, u27 pin 17
pin 29 (d4) = pin 29 on all PIAs, u16 pin 6, u28 pin 7, u25 pin 14, u26 pin 16, u27 pin 16
pin 30 (d3) = pin 30 on all PIAs, u16 pin 5, u28 pin 17, u25 pin 13, u26 pin 15, u27 pin 15
pin 31 (d2) = pin 31 on all PIAs, u16 pin 4, u28 pin 4, u25 pin 11, u26 pin 13, u27 pin 13
pin 32 (d1) = pin 32 on all PIAs, u16 pin 3, u28 pin 18, u25 pin 10, u26 pin 12, u27 pin 12
pin 33 (d0) = pin 33 on all PIAs, u16 pin 2, u28 pin 3, u25 pin 9, u26 pin 11, u27 pin 11
pin 34 (reset) = pin 34 on all PIAs, u15 pin 40, u43 pin 4, sr19 pin 3, q39 (top leg), r69 (rt leg)
pin 35 (rs1) = pin 35 on all PIAs (a1), u25 pin 9, u26 pin 9, u27 pin 9, u11 pin 16
pin 36 (rs0) = pin 36 on all PIAs (a0), u25 pin 10, u26 pin 10, u27 pin 10, u11 pin 14
pin 37/38 (irq) = pins 37/38 on all PIAs, r70 (rt leg), u32 pin 1
pin 39 (ca2) = u49 pin 9, sr17 pin 10
pin 40 (ca1) = gnd