Does anyone know what the self test positions 20-22 are for on 80's Bally games. For example, on Spy Hunter, after the usual 01-19 documented settings using the diagnostic button inside the coin door, there is a setting #20, with settable values from 00-15.

Elektra, Fathom, Centaur, Medusa also have settings in #20-22 range (some only go to #20, while some go as far as #22), all with settable values 00-15.

None of the manuals for these games document any settings above self test #19.

Bump...still wondering about these strange settings on some Bally games.

Its doing something. I'm just not sure what. I've been looking at the coding on Spy Hunter. When disassembled, there are 3 areas of code in the game ROM that call the setting for audit 20.

So, for example, audits 16-19 are stored in battery backed RAM at $2FA-$2FD. Audit 20 (the undocumented one) is stored at $2FE. When I search the code for $02FE, I get 3 hits...all in the game ROM, and they are fairly large routines.

1258: 4F clra
1259: B7 02 14 sta $0214
125C: B6 02 0A lda $020A
125F: 8A 40 ora #$40
1261: B7 02 0A sta $020A
1264: B6 02 FE lda $02FE <<<<<<<<<<<<<<<<<<<<<<<<
1267: 84 F0 anda #$F0
1269: 27 05 beq $1270
126B: 86 12 lda #$12
126D: BD 55 7C jsr $557C
1270: B6 02 17 lda $0217
1273: 8A 10 ora #$10
1275: CE 12 BF ldx #$12BF
1278: 08 inx
1279: 08 inx
127A: 48 asla
127B: 24 FB bcc $1278
127D: EE 00 ldx (x+$00)
127F: 6E 00 jmp (x+$00)
1281: BD 11 8C jsr $118C
1284: C6 20 ldb #$20
1286: 20 24 bra $12AC
1288: BD 11 9C jsr $119C
128B: C6 40 ldb #$40
128D: 96 4E lda $4E
128F: 85 08 bita #$08
1291: 26 02 bne $1295
1293: C6 C0 ldb #$C0
1295: 20 15 bra $12AC
1297: BD 51 55 jsr $5155
129A: 96 4E lda $4E
129C: 8A 08 ora #$08
129E: 97 4E sta $4E
12A0: BD 11 D7 jsr $11D7
12A3: C6 40 ldb #$40
12A5: 20 05 bra $12AC
12A7: BD 11 D7 jsr $11D7
12AA: C6 40 ldb #$40
12AC: F7 02 17 stb $0217
12AF: CE 02 00 ldx #$0200
12B2: C6 FF ldb #$FF
12B4: E7 11 stb (x+$11)
12B6: 96 51 lda $51
12B8: 43 coma
12B9: A7 06 sta (x+$06)
12BB: BD 10 7B jsr $107B
12BE: A7 05 sta (x+$05)
12C0: 39 rts
...........................................
13DF: 84 E0 anda #$E0
13E1: 26 A2 bne $1385
13E3: BD 11 1B jsr $111B
13E6: B6 02 FE lda $02FE <<<<<<<<<<<<<<<<<<<<<<<<<
13E9: 84 F0 anda #$F0
13EB: 27 05 beq $13F2
13ED: 86 12 lda #$12
13EF: BD 55 7C jsr $557C
13F2: BD 14 89 jsr $1489
13F5: CE 02 00 ldx #$0200
13F8: B6 02 12 lda $0212
13FB: 85 10 bita #$10
13FD: 27 32 beq $1431
13FF: 4F clra
1400: B7 02 12 sta $0212
1403: 86 FF lda #$FF
1405: A7 01 sta (x+$01)
1407: A7 02 sta (x+$02)
1409: 86 EF lda #$EF
140B: A7 00 sta (x+$00)
140D: BD 51 55 jsr $5155
1410: BD 11 94 jsr $1194
1413: 96 47 lda $47
1415: 2B 09 bmi $1420
1417: 96 4E lda $4E
1419: 8A 04 ora #$04
141B: 97 4E sta $4E
141D: 7E 14 79 jmp $1479

...............................................
566B: C5 10 bitb #$10
566D: 27 C5 beq $5634
566F: D6 0B ldb $0B
5671: C4 F0 andb #$F0
5673: C1 10 cmpb #$10
5675: 26 BD bne $5634
5677: F6 02 FE ldb $02FE <<<<<<<<<<<<<<<<<<<<<<<<<
567A: C4 F0 andb #$F0
567C: 27 B6 beq $5634
567E: 86 12 lda #$12
5680: BD 55 7C jsr $557C
5683: 20 AF bra $5634
5685: 39 rts

Normally that's the best way to get all the features turned on, but these settings (settings greater than #19) cycle from 00-15.

No. Settings #16-19 cycle 00-03. 16, 17, and 19 refer to score/award settings, and 18 refers to sound settings.

Was that optional hardware you could get from Bally, or a setting that affected the stock sound board (if you can remember)?