Welcome, here you will find the information taken from the original UK ZX81 instruction assembly instructions.
Please note that this document is for information purposes only :)
Click on the following descriptions to view the required file.
All the files are gif format
Circuit diagram - 546k
Component Layout - 26k
Regulator Heatsink Assembly Diagram - 9k
Keyboard Connector Assembly Diagram - 12k
Case Assembly - 25k
| Ref Number | Value | Comments |
| R1 | 10k | |
| R2 | 680R | |
| R3 | - | Not Used |
| R4 | 18k | |
| R5 | 330R | |
| R6 | 2k2 | |
| R7-R14 | 470R | |
| R15 | 220k | |
| R16-R27 | 1k | |
| R28 | 680R | |
| R29 | 1M | |
| R30 | - | Not Used |
| R31 | - | Not Used |
| R32 | - | Not Used |
| R33 | 4k7 | |
| R34 | 220R |
| Ref Number | Value | Comments |
| RP1 | 8 x 10k | 9 leads |
| RP2 | - | Not Used |
| RP3 | 5 x 10k | 6 leads |
| Ref Number | Value | Markings | Comments |
| C1 | 47pF | 47 | Ceramic disc |
| C2 | 47nF | 473 Z | Ceramic disc |
| C3 | 22uF | 22u | Electrolytic 16V minimum |
| C4 | 47nF | 473 Z | Ceramic disc |
| C5 | 1uF | 1u | Electrolytic 5V minimum |
| C6 | 100pF | 100, 101, n10 | Ceramic disc |
| C7 | 47pF | 47 | Ceramic disc |
| C8 | 47nF | 473 Z | Ceramic disc |
| C9 | 47nF | 473 Z | Ceramic disc |
| C10 | 10nF | 10n, 103 | Ceramic disc |
| C11 | 47nF | 473 Z | Ceramic disc |
| C12 | 47pF | 47 | Ceramic disc |
Please Note - The memory is either IC4a & IC4b or IC4.
| Ref Number | Type | Comment |
| IC1 | Sinclair Logic IC | 40 pin |
| IC2 | 2364 | 24 pin |
| IC3 | Z80A or D780C-1 | 40 pin |
| IC4 | MK4118 | 24 pin |
| IC4a | uPD2114LC | 18 pin |
| IC4b | uPD2114LC-1 | 18 pin |
| REG | 7805 | 5 volt regulator |
| TR1 | ZTX313 | |
| TR2 | ZTX313 | |
| D1-D8 | 1N4448 or 1N4148 or 1S4A | |
| D9 | - | Not Used |
| X1 | CDA 6.5MC | 3 lead ceramic filter |
Modulator Type UM1233
3 off 3.5mm jack sockets for power, ear and mic.
2 off 40 pin IC sockets.
Either 2 off 24 pin IC sockets
or 1 off 24 pin and 2 off 18 pin IC sockets.
KB1 5 way keyboard connector.
KB2 8 way keyboard connector.
Modulator trim (black card).
Ready made flat keyboard.
Aluminium heatsink.
4BA nut, bolt and washer for fixing regulator and heatsink.
Printed Circuit Board.
2 Case Halves.
4 Rubber feet.
7 self tapping Pozidriv screws - 3 Black (long), 4 Yellow (short).
Requests for further information and general mail to
Downloaded from The Lil Old Sinclair Computer Technical Information Repository
