ZX Spectrum 128
The toastrack: 128K, AY sound and a second ROM bank.
Open the ZX Spectrum 128 in Retro Bench- Also
- Toastrack 128K
- Year
- 1986
- CPU
- Z80A @ 3.5 MHz
- RAM
- 128 KB (banked)
- ROM
- Two 16 KB ROM banks
- Video
- ULA: 256 x 192, 8 colors
- Sound
- AY-3-8912 (3 voices) + beeper
- OS
- 128K BASIC
Chips
| Chip | Where | Role |
|---|---|---|
| Z80A CPU | Main CPU (8-bit, 40-DIP) | |
| Spectrum 128 / +2 / +3 ULA or gate array | Video, memory banking, ports (7K010E-5 on the 128; Amstrad 40056/40077 on later models) | |
| AY-3-8912 sound chip | IC32 | Three-voice programmable sound generator with one 8-bit I/O port |
Ports and connectors
- Power in (9V DC), 2.1 mm coaxial DC socket UNVERIFIED
- EAR (tape in), 3.5 mm mono jack
- MIC (tape out, sound out), 3.5 mm mono jack
- TV (UHF RF out), Phono socket, RF
- RGB monitor, DIN 8-pin 270° socket
- Rear edge connector (2 x 28), Card edge, 28 + 28 positions, keyway at 5 UNVERIFIED
- Keypad socket, BT 603A 6-way telephone socket UNVERIFIED
- RS232 / MIDI, BT 603A 6-way telephone socket UNVERIFIED
Power rails
| Rail | Expect | Measure at |
|---|---|---|
| +9 V DC in | 9 V nominal, unregulated | PWR socket; spectrum128-edge pin A4 |
| +5 V | +5 V | 7805 output; Z80A pin 11; spectrum128-edge pin A3 |
| +12 V | +12 V | TR4/TR5 inverter (D15/C44); RS232 driver IC33; keypad |
| -12 V | -5 V to -12 V, unregulated | Charge pump C111/C112, D28/D29; RS232 driver IC33 |
| -5 V | -5 V | Zener D19 from -12 V; spectrum128-edge pin B20 |
| GND | 0 V | Z80A pin 29; spectrum128-edge pins A6, A7, A14 |
Symptoms
- No menu, no picture: check ULA 128, Z80A
- RS232, MIDI and keypad dead
- No color or wrong color: check ULA 128
- Picture but no sound on the TV
- Crashes or garbage after reset: check Z80A, ULA 128
- No AY music, beeper works: check AY-3-8912, ULA 128
- TV will not tune in