Black screen, won't boot
Step-by-step diagnosis for the Amiga 1200 rev 2B board. Each step lights up the signal or chip to measure in the explorer below.
The power light comes on but the screen stays black, with no colour at all. Measure in order: each step is only worth it if the previous one is fine.
- VCCShow on board →
The 5 V rail
With the machine on, measure between a VCC pin and ground: it must read between 4.75 and 5.25 V. Below that, the power supply is usually to blame, not the board.
- _RESETShow on board →
Reset
After power-on, _RESET must go high (close to 5 V). If it stays stuck low, the processor never starts: follow the line to the reset circuit and the keyboard connector.
- 7MHZShow on board →
The clock
With a scope, there must be a clock of about 7 MHz reaching the processor. Without a clock nothing moves: check the crystal and the chip that generates it (Agnus or Alice).
- _ASShow on board →
The processor at work
_AS pulses every time the processor accesses memory. If it pulses, the processor is alive and the fault is further along. If it is still, go back to reset and the clock.
- _ROMENShow on board →
The ROM
_ROMEN selects the Kickstart ROM. If it pulses and still no colour appears, suspect the ROM or its socket: clean the contacts and reseat it.
Didn't fix it?
We repair these boards on our bench in Loures. The request already includes the board and the fault.
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