The IBM 31SD is a 1970s 8 inch floppy drive that was used in several different systems of theirs, including the IBM 3274-51C (and -52C) terminal controller and the IBM 5280 Distributed Data System.
It has a small circuit board with some analog circuitry for reading and writing data as well as controlling the head load solenoid and head stepper motor.
The circuit board is partially documented in the following sources:
IBM 3270 Control Unit Models 51C and 52C Maintenance Concepts - This document contains a block diagram of the card on PDF page 170.
IBM 5280 Distributed Data System Diskette Drive Maintenance Manual - This document is less useful and contains mostly duplicate information, although the block diagram is missing.
Unfortunately there is no schematic, and the parts only have seven-digit IBM internal part numbers. There are partial lists of these part numbers on the internet in various places, but most of the parts on this board have no documentation whatsoever.
In the off-chance that someone might find this useful, I've completely reverse engineered the card and documented information about the IBM part numbers.
See the schematic PDF.
Here is a list of IBM part numbers on this board along with information about each. I have not included physical locations or designators but they can be implied from the schematic.
A quick note about IBM part numbers: They are often divided into a group of three numbers and a group of four numbers with a space in between. Some components truncate the part number, showing only the last 3, 4, or 5 digits.
| IBM part number | Description |
|---|---|
| Integrated circuits | |
| 2392100 | Equivalent to a TTL 7400 NAND gate. |
| 2392102 | Equivalent to a TTL 7404 inverter. |
| 1582979 | Marked "2979". Equivalent to an MC1472 NAND driver. |
| 2396475 | Equivalent to a uA723 (or LM723) voltage regulator (in 10-pin TO-100). |
| 5616846 | Detector. This converts filtered analog disk data into digital flux transitions. |
| 5616847 | Amplifier-differentiator. This amplifies the analog head signal and differentiates it. |
| 5897738 | Preamp. This amplifies the read signal from the head or, when in write mode, drives pulses into the head. |
| Resistor arrays (RPAKs) | |
| 2392471 | 4-pin, 3 resistor, each 90 ohms. Pin 1 is the common pin. |
| 2392488 | 4-pin, 3 resistor, each 400 ohms. Pin 1 is the common pin. |
| 2392787 | 6-pin, 4 resistor, each 1K. Resistors on pins 1 and 2 are bussed to pin 3, and resistors on pins 5 and 6 are bussed to pin 4. |
| 2408334 | 4-pin, 2 resistor, each 121K ohms. Pins 1 and 2 is one resistor, pins 3 and 4 are the other resistor. |
| 2408846 | 8-pin, 2 resistor, each 95 ohms. Pins 1 and 4 is one resistor, pins 5 and 8 are the other resistor. Presumably this resistor can handle higher power levels. |
| Tantalum capacitors | |
| 1589440 | Marked "440". 0.68uF 50V. |
| 2396951 | Marked "951". 8.2uF 12V. |
| 5616808 | Marked "808". 3.9uF 20V. |
| Ceramic capacitors | |
| 1539475 | Marked "9475". 0.1uF +/-10% 25V X5R. |
| 1589422 | Marked "9422". 0.01uF +/-15% 50V X5R. |
| 2391271 | Marked "1271". 120pF +/-10% 100V Z5E. |
| 5616796 | Marked "6796". 68pF +/-5% 50V NP0. |
| 5616797 | Marked "6797". 180pF +/-5% 50V NP0. |
| Film Capacitor | |
| 0491309 | Marked "491 309 123 8210". 2.7nF +/-5% 100V mylar film. |
I'm less certain about part numbers for other devices on this board:
- Diode, glass package, marked 66 234 GG with a Fairchild logo.
- Diode, rectifier, marked G1419U.
- Transistor, probably NPN, marked 194 U8227K. The important bit is the "194" and the rest is a date code. It has a Motorola logo.
- Transistor, probably PNP, marked 131 U 213H. The important bit is the "131" and the rest is a date code. It has what appears to be a Fairchild logo.