View Single Post
Old 29th December 2015
Gear Maniac

1. 7805 +5V regulator. Its capacitors are to its upper left, its resistor right above it.

2. 7493N 'S' logo. 4-bit binary counter.
3. Xtal section. Xtal is marked 8.00 MHz

4. MC74HC00AN Motorola logo. quad 2-input NAND gate
5. Z80. Didn't write down the full number.

6. ROM. Most of it is covered by the paper JL Cooper lable. Verison is 2. something. 21V FAST peek out from under the label.

7. 98851 'ST' logo. STMicroelectronics 2K x 8 CMOS STATIC RAM

8. 2 8927 'ST' logo. Asynchronous Communications Interface Adapter (2 MHz).

9. MC74HC138AN Motorola logo. 3 to 8-line decoder/demultiplexer

10. 8461A0 Mitsubishi logo. quad 2-input OR gate

11. Array of transistors and resistors. Probably LED drivers.

12. 8424KO Mitsubishi logo. BCD to decimal decoder Note the 'LS' on this one, bipolar, not CMOS.

13. P8936G Double-lightning logo. octal register with three-state outputs

14. 7406 PC 'F' logo. hex inverter buffer/driver with 30 V open collector outputs
8419(?) Singapore

15. MC74HC244AN Motorola logo. octal buffer with noninverted three-state outputs

16. PS 900V Optoisolator. Required by MIDI electrical spec.

17. CD221003 I couldn't find this one. Might be CD22103? CMOS HDB3 (High Density Bipolar 3) Transcoder for 2.048/8.448Mb/s Transmission Applications
RCA H 823

18. M74HC151B1 'SCS' logo. 8-line to 1-line data selector/multiplexer

19. CD74HC22106E QMOS 8 x 8 x 1 Crosspoint Switch with Memory Control
RCA Z 906

20. Battery. After replacement.

Most of it makes perfect sense to me, except that CD221003 (or 03).

Pretty clever circuit. I wondered how they moved data from 8 MIDI ins to 8 MIDI outs with a processor of the time. Turns out they probably use that CD74HC22106E to just make it a bunch of THRU ports. Very cool.
Attached Thumbnails
JL Cooper MSB+ REv. II troubleshooting/fixing.-msb.jpg