Schematic
Miida MC800 Calculator: Reverse-Engineered Schematic
Schematic of the Miida MC800 of 1971: Omron ALPHA1-3 chip set, discrete A628A PNP drivers to -58 V, NEC LD8027 single-digit tubes, lamps for minus and overflow, inter-digit blanking.
Schematic
Schematic of the Miida MC800 of 1971: Omron ALPHA1-3 chip set, discrete A628A PNP drivers to -58 V, NEC LD8027 single-digit tubes, lamps for minus and overflow, inter-digit blanking.
Q23 Q24 C711 C711 100K 100K V–15 V–15 NDL.9 NDL.12 – 108 NDL.11 V–2 1 V–15 1 2.2 14 2 Q15 Ø1 Sn Ø1 nSa 13 22 3 12(19) A628A 25V Ø2 So Ø2 100K 23 15K 510 22 V–15 6 21 100K V–15 7 NK.12 24 NDL.3 V–58 8 10 NDL.7 12 nSb Q16 each 10,17 5 U2 13(18) NDL.6 C 9 25 key NK.2 nSc Q17 14 9• NDL.4 OMRON nSd Q18 100K 15 ALPHA2 NDL.8 nSe Q19 25 16 NDL.5 nSf Q20 NK.4 U1 17 NDL.10 26 nSg Q21 28 20 NK.6 n.c.: NDL.1 27 OMRON 23 Q22 6,7,8,9,11,26 NK.8 ALPHA1 27 28 a NK.10 4 NDR.10 V–15 f b g NDR.9 (21) 2 e c 7 8 9 NEC NK.7 LD8027 1 5 6 7 V–2 d p 4 5 6 ÷ (20) 3 14 Ø1 nSp NK.5 19 16 Ø2 Q14 (19) 4 nT8 1 2 3 += 4 21 A628A NK.3 n.c.: 11,15,24 22K 9 NDR.8 CE 0 . –= (18) 5 18 V–15 10K NK.1 10 16 11 U3 V–58 V–15 V–15 8 NDR.7 NDR.11 nT7 Q13 3 24 OMRON NDR.6 12 nT6 Q12 NDR.9 26 ALPHA3 Q11 NDR.5 nT5 28 NDR.4 nT4 Q10 23 NDR.3 nT3 Q9 25 NDR.2 n.c.: 13,17 nT2 Q8 27 (22) NDR.1 nT1 Q7 2 (20) 15 V–15 Miida Model MC800 Calculator Page: 1 of 2 Printed: 2021 Jan 30 28µS 7µS Ø1 2.7K 14µS 7µS Ø1 5.6K 100K 5.6K 200p 100K 200p 5.6K Ø2 Q5 C711 150p Q4 Q3 15K C711 C711 nTx V–25 2.7K nSy V–15 Ø2 5.6K Q6 C711 nT(x+1) 150p 15K Ø1 & Ø2 measured = 35.9KHz = 27.9µS V–25 Digit pulses (Tx) are 3•Ø2 with 1•Ø2 inter-digit. Number cycle is 10•4•Ø2 (~ 900Hz). Digit pulses are only present for non-blank digits. Segment lines may be asserted during blanked digits. Display Board Q1 (component side) NP.11,12 2SD92 NP.9 33 S:1 / C:2 C:12 / S:11 10V NP.10 NDL NDR 33K V–2 Q2 S:11 / C:12 C:2 / S:1 og NP.5 1K C711 100 10 POWER 0.125A 0.047 25V 470 4.7 bn og 25V 25V S: 11 1 NP.6 NP 2.2 C: 12 2 115V bu 0.047 V–15 gn NP.7 50V 12K 240V 47 50V 3.3K V–25 Main Board bk bu (component side) NP.8 NDR.2 V–58 rd yl NP.1,2 NDL.11 yl NDL.12 Q6 Q3 Q4 Q5 Q2 Q23 NP.3,4 Q24 display tube filaments p b f a Notes Q14 Q7 Q22 Q16 Q20 Q15 Q21 Q19 Q17 Q18 • Capacitance in microfarads unless otherwise specified. g e c d • Based on unit missing the case. Serial number unknown. • 1996 Jan 17: Initial drawing / bhilpert U1 2020 Jan: Format updates / bh. U3 U2 2021 Jan: Timing diagram & connector pin id added / bh. Miida Model MC800 Calculator Component side: 2 12 NK Page: 2 of 2 Printed: 2021 Jan 30 Solder side: 1 11