BBC Micro Model A/B Troubleshooting Guide: Difference between revisions
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This guide details systematic troubleshooting for the '''BBC Micro Model A and Model B''' home computers. These classic 8-bit systems are robust but now decades old, so methodical diagnosis is essential for reliable restoration and repair. | This guide details systematic troubleshooting for the '''BBC Micro Model A and Model B''' home computers. These classic 8-bit systems are robust but now decades old, so methodical diagnosis is essential for reliable restoration and repair. | ||
== | == Preliminary & Power-up Checks == | ||
Begin by confirming the BBC Micro receives correct voltages and basic startup conditions. Many faults stem from power or socket issues rather than failed chips. | Begin by confirming the BBC Micro receives correct voltages and basic startup conditions. Many faults stem from power or socket issues rather than failed chips. | ||
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If any of these are missing, proceed to the next section. | If any of these are missing, proceed to the next section. | ||
== | == Display & Chime Diagnostics == | ||
The BBC Micro provides clear visual and audio cues at startup. Use these to narrow down faults. | The BBC Micro provides clear visual and audio cues at startup. Use these to narrow down faults. | ||
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* UHF output (RF modulator) – test with analogue TV, channel 36 (UK). | * UHF output (RF modulator) – test with analogue TV, channel 36 (UK). | ||
== | == Memory & ROM Faults == | ||
RAM and ROM failures are common in ageing BBC Micros, especially with original DRAM chips. | RAM and ROM failures are common in ageing BBC Micros, especially with original DRAM chips. | ||
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*ROMs are typically 27128 or 27128-compatible EPROMs; always observe correct orientation.* | *ROMs are typically 27128 or 27128-compatible EPROMs; always observe correct orientation.* | ||
== | == Connector & Socket Issues == | ||
Loose or oxidised sockets are a frequent cause of intermittent faults. | Loose or oxidised sockets are a frequent cause of intermittent faults. | ||
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* Check for broken solder joints on the power socket and video connectors. | * Check for broken solder joints on the power socket and video connectors. | ||
== | == Component-level Tests == | ||
=== Clock & Reset === | === Clock & Reset === | ||
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* Check for activity on the NMI and IRQ lines (CPU pins 6 and 4). | * Check for activity on the NMI and IRQ lines (CPU pins 6 and 4). | ||
== | == Audio & I/O Failures == | ||
{| class="wikitable styled-table" | {| class="wikitable styled-table" | ||
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|} | |} | ||
== | == Storage & Expansion Issues == | ||
=== Floppy Disk Problems (Model B or upgraded A) === | === Floppy Disk Problems (Model B or upgraded A) === | ||
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* "No ROM at ..." or language not found: check sideways ROM sockets, orientation, and supply voltage. | * "No ROM at ..." or language not found: check sideways ROM sockets, orientation, and supply voltage. | ||
== | == Error & Beep Code Table == | ||
The BBC Micro uses beep codes for basic error reporting at power-on. | The BBC Micro uses beep codes for basic error reporting at power-on. | ||
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* Never operate the BBC Micro with missing or incorrect voltage rails, especially -5V on early DRAM boards. | * Never operate the BBC Micro with missing or incorrect voltage rails, especially -5V on early DRAM boards. | ||
== | == Related Pages == | ||
* [[BBC Micro Model A/B Capacitor Replacement Guide]] | * [[BBC Micro Model A/B Capacitor Replacement Guide]] | ||
* [[BBC Micro ROM Upgrades]] | * [[BBC Micro ROM Upgrades]] | ||