Stripes, squares or missing memory
Step-by-step diagnosis for the ZX Spectrum 48K Issue 2 board. Each step lights up the signal or chip to measure in the explorer below.
It boots with vertical stripes, squares or garbage on screen, or seems to have less memory than it should.
- IC6 · 4116Show on board →
The lower 16K
The eight 4116s hold the screen. A bad one gives vertical stripes or squares at boot; it is often the one that runs hotter than the rest.
- -5VShow on board →
Before replacing a 4116
Check −5 V and +12 V: a missing rail is often what killed the memory, and it would kill the new chips too.
- IC15 · 4532Show on board →
The upper 32K
If they fail, the 48K may boot as if it had less memory. PRINT PEEK 23733 gives 255 on a healthy 48K and 127 on a 16K.
- IC25 · 74LS157Show on board →
The upper multiplexers
They select the address for the upper memory. The service manual warns that National Semiconductor 74LS157s don’t work here.
Didn't fix it?
We repair these boards on our bench in Loures. The request already includes the board and the fault.
Loading the board…
Drag to move; mouse wheel or two fingers to zoom. Tap a pad to follow the signal.