I have a Heathkit H89A I acquired some years ago with a note attached "Bad keyboard encoder on terminal card." Is anyone here familiar with the keyboard encoder? I sort of recall reading somewhere that the keyboard encoder is not available anymore and before I start into this YAP (Yet Another Project), it would be nice to know if there is any hope of repairing this thing somewhat easily.

Sure am.... I have the Z90 manual here, which is essentially the same machine... The keyboard encoder is the 40 pin chip at location U444 on the terminal logic board. The terminal logic board is the large board standing vertically at the very back of the machine, and U444 is just above the connector for the keyboard ribbon cable. The keyboard encoder has the Heath/Zenith part number 443-913, and is described as an S470 keyboad encoder in the IC specifications list. I am told that there was a standard keyboard encoder with much the same pinout, but with different internal programming, so the output codes for some of the keys are different. However AFAIK, all H88s, H89s, Z90s and H/Z19 terminals use the same encoder chip, so if you find a dead example of any of those machines, it's a possible source of the chip. The output of the keyboard encoder chip goes to a ROM, U445 (444-37) on the terminal logic board. This translates the keyboard codes into ASCII (and special codes for the non-standard keys). Whether you could use a standard encoder if you reprogrammed the ROM, I don't know. For reference, the pinout of the keyboard encoder chip is : 1 B3 (bit 3 output) (=A2) 2 Vll (ground) 3 clock input 4 X9 (keyboard scan output) 5 X8 6 X7 7 X6 8 X5 9 X4 10 X3 11 X2 12 X1 13 Data strobe output 14 Data strobe control 15 Output Enable 16 Repeat 17 Key bounce mask 18 Vgg (-12V) 19 Control key input 20 Shift lock I/D 21 Shift 22 Y10 (keyboard input) 23 Y1 24 Y2 25 Y3 26 Y4 27 Y5 28 Y6 29 Y7 30 Y8 31 Y9 32 Vss (+5V) 33 B5 (=A4) 34 B6 (=A5) 35 B7 (=A7, control output) 36 B8 (=A8, shift output) 37 B1 (=A0) 38 B2 (=A1) 39 B9 (=A6) 40 B4 (=A3) The B-lines are scambled before being connected to the ROM -- I've put the assignments in brackets above). A9 and A10 on the ROM are groudned. The address inputs to the ROM for each key are : f1 0a f2 2a f3 1a f4 3a f5 4a Erase 6a Blue 5a Red 7a Grey 06 Esc 2d 1 05 2 25 3 15 4 35 5 45 6 65 7 55 8 75 9 0d 0 5c - 7c = 02 ` 22 Bsp 12 Tab 79 Q 51 W 71 E 09 R 29 T 19 Y 39 U 49 I 69 O 59 P 44 [ 64 \ 54 LF 74 Del 0C A 4E S 6E D 5E F 7E G 01 H 21 J 11 K 31 L 41 ; 18 ' 38 { 48 Ret 68 Scroll 61 Z 16 X 36 C 46 V 66 B 56 N 76 M 0E , 2E . 1E / 00 Space 3E K0 50 K. 70 Kenter 08 K1 04 K2 24 K3 14 K4 1C K5 3C K6 4C K7 42 K8 62 K9 52 NU1 32 NU2 40 (K-prefixed keys are on the number pad) The outputs of the ROM -- i.e. what the firmware on the terminal logic card is expecting -- for each key are : key norm shift ctrl s&c f1 00 00 80 80 f2 01 01 81 81 f3 02 02 82 82 f4 03 03 83 83 f5 04 04 84 84 Erase 05 05 85 85 Blue 06 06 86 86 Red 07 07 87 87 Grey 0e 0e 8e 8e Esc 1b 1b 9b 9b 1 31 21 b1 a1 2 32 32 b2 b2 3 33 23 b3 a3 4 34 24 b4 a4 5 35 25 b5 a5 6 36 36 b6 b6 7 37 37 b7 b7 8 38 38 b8 b8 9 39 39 b9 b9 0 30 30 b0 b0 - 2d 2d ad ad = 3d 3d bd bd ` 60 60 e0 e0 Bsp 08 08 88 88 Tab 09 09 89 89 Q 71 51 f1 d1 W 77 57 f7 d7 E 65 45 e5 c5 R 72 52 f2 d2 T 74 54 f4 d4 Y 79 59 f9 d9 U 75 55 f5 d5 I 69 49 e9 c9 O 6f 4f ef cf P 70 50 f0 d0 [ 5b 5b db db \ 5c 7c dc fc LF 0a 0a 8a 8a Del 7f 7f ff ff A 61 41 e1 c1 S 73 53 f3 d3 D 64 44 e4 c4 F 66 46 e6 c6 G 67 47 e7 c7 H 68 48 e8 c8 J 6a 4a ea ca K 6b 4b eb cb L 6c 4c ec cc ; 3b 3b bb bb ' 27 27 a7 a7 { 7b 7b fb fb Ret 0d 0d 8d 8d Scroll 1f 1f 9f 9f Z 7a 5a fa da X 78 58 f8 d8 C 63 43 e3 c3 V 76 56 f6 d6 B 62 42 e2 c2 N 6e 4e ee ce M 6d 4d ed cd , 2c 3c ac bc . 2e 3e ae be / 2f 3f af bf Space 20 20 a0 a0 K0 10 10 90 10 K. 1a 1a 9a 9a Kenter 1c 1c 9c 9c K1 11 11 91 91 K2 12 12 92 92 K3 13 13 93 93 K4 14 14 94 94 K5 15 15 95 95 K6 16 16 96 96 K7 17 17 97 97 K8 18 18 98 98 K9 19 19 99 99 NU1 0b 0b 8b 8b NU2 0c 0c 8c 8c While this might be more work than you want, the above should allow you to create something that will work... -tony