Schematic
Miida MC840 Calculator: Reverse-Engineered Schematic
Schematic of the Miida MC840 desk calculator of 1972 with an Ise DP82A eight-digit fluorescent tube.
Schematic
Schematic of the Miida MC840 desk calculator of 1972 with an Ise DP82A eight-digit fluorescent tube.
12 10• 10• 11 100K 11 100K Ø1 nSn U6 19 12 21 2.2 Ø2 9 nSo U6 25V 18 10 150K 510 12 10 11 3 R12 V–16 Ø1 nSa U6 Sa ISE NO. DP82A 01220 20 15 NK.5 21 8 DIGIT VACUUM FLOURESCENT Ø2 3 L1 nSb U4 Sb DISPLAY MODULE 7 18 15 each 20 10 6 R10 C 6 nSc U6 Sc key NK.8 13 15 13 a 5 108 6 L4 f b 22 14 nSd U4 Sd g R8 K 8 14 13 latch NK.6 15 U2 4 L3 4 9 nSe U4 Se e c 16 OMRON 16 14 R5 NK.1 3 1 L2 17 HD32105P nSf U4 Sf d p 5 19 16 U1 13 NK.3 4 R11 D8 D1 D0 6 OMRON 22 nSg 17 U6 14 Sg NK.5 HD32104P 4 1 R9 U6 Sp 9 16 n.c.: 3 23 NK.11 L12 L11 L10 L9 L8 R4 R3 R2 R1 24 V–16 V–55 23 2 1 7 8 9 NK.4 V–16 V–9 24 4 5 6 ÷ 12 NK.2 11 8 Ø1 nSp 8 of 8 of 1 2 3 += 21 7 NK.9 Ø2 100K 11 22K nT8 U4 3 18 12 7 9 CE 0 . –= 4 nT7 U4 NK.7 17 10 5 1 nT6 U5 22 16 16 3 2 1 23 U3 nT5 15 U5 15 V–16 V–9 24 OMRON 4 nT4 U5 HD32106P 14 14 20 6 19 nT3 U5 9 13 8 11 nT2 U5 10 12 9 nT1 U5 13 10 470K 6 V–16 V–55 0.047 2 1 V–16 V–16 V–9 Miida MC840 Calculator Page: 1 of 2 Printed: 2021 Jan 30 27µS 2.2K 9µS Ø1 2• Ø1 5.6K 250p 150p 5.6K 200p 100K Q4 16µS 5µS 5.6K C711 Q3 Q2 18K Ø2 C711 C711 V–16 nTx 2.2K V–16 Ø2 50p Q5 nSy 5.6K C711 18K nT(x+1) V–16 Ø1 & Ø2 measured = 36.4KHz = 27.4µS Digit pulses (Tx) are 4•Ø2 . Number cycle is 10•Tx (~ 900Hz). Segment pulses (Sy) are 3•Ø1. Q1 Main Board C1162 (component side) yl NP.3 2 5 7 8 33 NP.1 18 1K 8.8V Q3 Q2 100 16V Q1 VAC 25V U4,5,6 22 0.047 yl 2.2 150 V–9 TM4352P NP.6 16.3V 25V POWER 50V Q5 Q4 NP.4 bk og NP.5 V–16 5.6K rd 32 47 115V VAC 50V –45V 5W 9.2V 240V bn og NP.6 U4 U5 U6 R6 V–55 bu NP.1 1.8 VAC(m) L5 bu L7 L6 NP.2 U3 U2 U1 display filaments (flags digit has double filament) component side NK.2 solder side NK.1 NK.11 Notes • Capacitance in microfarads unless otherwise specified. • Based on unit with Serial No. 722638. • 2000 Jan: Initial drawing / bhilpert. 2020 Jan: Format updates / bh. 2021 Jan: 1->2 pages, timing diagram added / bh. Miida MC840 Calculator Page: 2 of 2 Printed: 2021 Jan 30