ZX Spectrum 48K
ULA, 4116 lower RAM, multi-rail PSU.
Open the ZX Spectrum 48K in Retro Bench- Also
- Spectrum 16K / 48K
- Year
- 1982
- CPU
- Z80A @ 3.5 MHz
- RAM
- 48 KB (16K 4116 lower, 32K upper)
- ROM
- 16 KB BASIC ROM
- Video
- ULA: 256 x 192, 8 colors, attribute clash
- Sound
- Beeper (1-bit)
- OS
- Sinclair BASIC
Chips
| Chip | Where | Role |
|---|---|---|
| Spectrum ULA 5C102E / 6C001E | IC1 | Video, lower RAM timing and contention, keyboard, beeper, tape |
| Z80A CPU | IC2 | Main CPU (8-bit, 40-DIP) |
| 4116 DRAM 16K x 1 | IC6-IC13 | Dynamic RAM, 16K x 1 (lower 16K on the Spectrum) |
| 4532 / 3732 DRAM 32K x 1 (upper 32K) | IC15-IC22 | Upper 32K on the 48K Spectrum |
| 23128 Mask ROM 16K×8 | IC5 | BASIC and KERNAL ROMs (C16, Plus/4, C64C short board, C128) |
Ports and connectors
- Power in (9V DC), 2.1 mm coaxial DC socket
- EAR (tape in), 3.5 mm mono jack
- MIC (tape out), 3.5 mm mono jack
- TV (UHF RF out), Phono (Cinch) socket, RF
- Rear edge connector (2 x 28), Card edge, 28 + 28 positions, keyway at 5
Power rails
| Rail | Expect | Measure at |
|---|---|---|
| +9 V DC in | +9 V ±2 V (7 to 11 V) | C50 positive side; spectrum-edge pin A4 |
| +5 V | +4.75 to +5.25 V, no visible ripple | C34 positive side; 4116 pin 9 (IC6); ULA pin 14; Z80A pin 11; spectrum-edge pin A3 |
| +12 V | +10.8 to +13.2 V UNVERIFIED | DC-DC converter (D15/C44); 4116 pin 8 (IC6); spectrum-edge pin B22 |
| +12 VA | +10.8 to +13.2 V | LT side of C52, to IC14 (LM1889) only |
| -5 V | -4 V to -5.5 V | DC-DC converter; 4116 pin 1 (IC6); spectrum-edge pin B20 |
| GND | 0 V | Z80A pin 29; ULA pin 40; 4116 pin 16; 23128 pin 14 (ROM IC5) |
Symptoms
- No picture: check ULA, 4116
- Dead, smoke at switch-on: check 4116
- Dead lower RAM (crash, garbage in the low 16K): check 4116
- Crash above $8000 (upper RAM): check 4532
- No boot: check Z80A, 23128
- No beep or tape: check ULA
- Keyboard membrane: dead keys: check ULA
- Hot ULA runs slow or crashes: check ULA