BBC Micro Model A/B Capacitor Replacement Guide: Difference between revisions
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Recapping a '''BBC Micro Model A or B''' is essential for ensuring stable power delivery, protecting irreplaceable ICs, and preventing damage from capacitor leakage. After four decades, the original electrolytic capacitors in these machines are often degraded or failing, causing unreliable operation, video instability, audio noise, or even catastrophic PCB corrosion. Proactive replacement preserves your BBC Micro for years to come. | Recapping a '''BBC Micro Model A or B''' is essential for ensuring stable power delivery, protecting irreplaceable ICs, and preventing damage from capacitor leakage. After four decades, the original electrolytic capacitors in these machines are often degraded or failing, causing unreliable operation, video instability, audio noise, or even catastrophic PCB corrosion. Proactive replacement preserves your BBC Micro for years to come. | ||
== | == Visual Inspection & Failure Signs == | ||
Before starting, examine all electrolytic capacitors for: | Before starting, examine all electrolytic capacitors for: | ||
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If any capacitor shows signs of failure, '''replace all electrolytics''' on the mainboard and power supply. Even apparently “good” capacitors may be out of tolerance or about to fail. | If any capacitor shows signs of failure, '''replace all electrolytics''' on the mainboard and power supply. Even apparently “good” capacitors may be out of tolerance or about to fail. | ||
== | == BBC Micro Capacitor Lists == | ||
The BBC Micro Model A and B use a mixture of through-hole aluminium electrolytic capacitors, both on the mainboard and in the internal power supply unit (PSU). All values below are for original Issue 3–7 boards and standard Astec AA11040C PSU; always cross-check your board’s silkscreen and PSU label. | The BBC Micro Model A and B use a mixture of through-hole aluminium electrolytic capacitors, both on the mainboard and in the internal power supply unit (PSU). All values below are for original Issue 3–7 boards and standard Astec AA11040C PSU; always cross-check your board’s silkscreen and PSU label. | ||
=== | === Mainboard Electrolytic Capacitors === | ||
{| class="wikitable styled-table" style="width:100%; text-align:center;" | {| class="wikitable styled-table" style="width:100%; text-align:center;" | ||
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| C8 || 10 µF || 16 V || Audio path (DC block) | | C8 || 10 µF || 16 V || Audio path (DC block) | ||
|- | |- | ||
| C9 || | | C9 || 10 µF || 16 V || Main 5 V rail decoupling (critical) | ||
|- | |- | ||
| C10 || 10 µF || 16 V || Audio path (DC block) | | C10 || 10 µF || 16 V || Audio path (DC block) | ||
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''Some later Issue 7 boards use 25 V rated parts for all 10 µF capacitors. Use 25 V or higher if in doubt.'' | ''Some later Issue 7 boards use 25 V rated parts for all 10 µF capacitors. Use 25 V or higher if in doubt.'' | ||
=== | === Power Supply Unit (Astec AA11040C) Electrolytic Capacitors === | ||
{| class="wikitable styled-table" style="width:100%; text-align:center;" | {| class="wikitable styled-table" style="width:100%; text-align:center;" | ||
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''Some PSUs use slightly different numbering or values (e.g., 330 µF for C1 in rare variants). Always check the markings on your PSU before ordering replacements.'' | ''Some PSUs use slightly different numbering or values (e.g., 330 µF for C1 in rare variants). Always check the markings on your PSU before ordering replacements.'' | ||
== | == Recapping Procedure == | ||
# '''Unplug the BBC Micro and allow it to sit for at least 10 minutes.''' | # '''Unplug the BBC Micro and allow it to sit for at least 10 minutes.''' | ||
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# '''Reassemble and test''' – Refit the mainboard and keyboard, reconnect all cables, and reassemble the case. | # '''Reassemble and test''' – Refit the mainboard and keyboard, reconnect all cables, and reassemble the case. | ||
== | == Recommended Tools & Parts == | ||
* '''Temperature-controlled soldering iron''' (60–80 W, 2 mm chisel tip) | * '''Temperature-controlled soldering iron''' (60–80 W, 2 mm chisel tip) | ||
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* '''Protective eyewear and ESD precautions''' | * '''Protective eyewear and ESD precautions''' | ||
== | == Post-Recap Voltage & Ripple Checks == | ||
After recapping, check the main voltage rails at the user port or directly on the mainboard: | After recapping, check the main voltage rails at the user port or directly on the mainboard: | ||
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''If ripple exceeds these values, re-check PSU capacitor installation and soldering.'' | ''If ripple exceeds these values, re-check PSU capacitor installation and soldering.'' | ||
== | == Additional Tips == | ||
* '''Replace all electrolytics together''' – If one has failed, the rest are not far behind. | * '''Replace all electrolytics together''' – If one has failed, the rest are not far behind. | ||
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* '''Power up with a current-limited bench supply or fused mains lead''' after recapping the PSU. | * '''Power up with a current-limited bench supply or fused mains lead''' after recapping the PSU. | ||
== | == Related Pages == | ||
* [[BBC Micro Troubleshooting | * [[BBC Micro Model A/B Troubleshooting Guide]] | ||
[[Category:BBC Micro]] | |||
[[Category:Acorn Computers]] | |||
[[Category:Capacitor Replacement Guides]] | |||