Commodore PET 2001 Capacitor Replacement Guide: Difference between revisions
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The first-generation '''PET 2001''' (1977 – 1979)—assemblies 320008 / 320081 / 320132—uses a simple linear supply together with an internal 9" monochrome CRT. | The first-generation '''PET 2001''' (1977 – 1979)—assemblies 320008 / 320081 / 320132—uses a simple linear supply together with an internal 9" monochrome CRT. After forty-plus years, the original electrolytic capacitors are at (or past) their design life. Re-capping: | ||
After forty-plus years, the original electrolytic capacitors are at (or past) their design life. Re-capping: | |||
* stabilises the +5 V / +12 V rails used by the logic and VIC video section, | * stabilises the +5 V / +12 V rails used by the logic and VIC video section, | ||
| Line 8: | Line 7: | ||
* protects irreplaceable ICs such as the '''6502''', the twin '''6520/6522 PIA/VIA''' I/O chips, and the early mask ROM/SRAM devices. | * protects irreplaceable ICs such as the '''6502''', the twin '''6520/6522 PIA/VIA''' I/O chips, and the early mask ROM/SRAM devices. | ||
'''''Tip ►''' The PET will usually still boot with tired capacitors—but voltages sag as it warms up, causing random lock-ups and screen collapse. Fix the caps before chasing “mystery” digital faults.'' | |||
== | == Visual Inspection == | ||
* '''Bulging or domed tops''' – particularly the two large 4 700 µF smoothing cans (C9 & C10). | * '''Bulging or domed tops''' – particularly the two large 4 700 µF smoothing cans (C9 & C10). | ||
* '''Brown crust''' or green verdigris at the rubber bungs. | * '''Brown crust''' or green verdigris at the rubber bungs. | ||
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If any of the above are present, _replace the whole set_ – piecemeal swaps often lead to repeated strip-downs. | If any of the above are present, _replace the whole set_ – piecemeal swaps often lead to repeated strip-downs. | ||
== | == Capacitor Reference Tables == | ||
Values are taken from Commodore parts sheets '''parts-3.gif''' (system board) and '''parts-6.gif''' (video board) for the PET 2001 series. Board lettering differs slightly between early 6540/6550 “static” boards (320008) and later 2316B/2114 “dynamic” boards (320132); positions are therefore given as '''silkscreen “Cx” + functional description'''. | Values are taken from Commodore parts sheets '''parts-3.gif''' (system board) and '''parts-6.gif''' (video board) for the PET 2001 series. Board lettering differs slightly between early 6540/6550 “static” boards (320008) and later 2316B/2114 “dynamic” boards (320132); positions are therefore given as '''silkscreen “Cx” + functional description'''. | ||
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''Use '''105 °C low-ESR''' parts for C9–C13—they run hot next to the transformer.'' | ''Use '''105 °C low-ESR''' parts for C9–C13—they run hot next to the transformer.'' | ||
=== | === CRT (Video/Deflection) Board === | ||
{| class="wikitable styled-table" style="width:100%; text-align:center;" | {| class="wikitable styled-table" style="width:100%; text-align:center;" | ||
|+'''9″ Monitor / Deflection Section''' | |+'''9″ Monitor / Deflection Section''' | ||
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'''Safety!''' C101 & C102 sit at ~160 V DC. Discharge them _with a 100 kΩ 2 W resistor_ before desoldering. | '''Safety!''' C101 & C102 sit at ~160 V DC. Discharge them _with a 100 kΩ 2 W resistor_ before desoldering. | ||
=== | === Optional Dynamic-RAM Board (PET 2001-8 upgrade) === | ||
Early 2001-8 machines add a small plug-in board carrying four 2114 SRAMs and four 10 µF / 16 V electrolytics (C201–C204). Replace these at the same time. | Early 2001-8 machines add a small plug-in board carrying four 2114 SRAMs and four 10 µF / 16 V electrolytics (C201–C204). Replace these at the same time. | ||
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# Run the PET for '''30 min burn-in'''; touch-test that the 7805 < 65 °C and C101/C102 remain cool. | # Run the PET for '''30 min burn-in'''; touch-test that the 7805 < 65 °C and C101/C102 remain cool. | ||
== | == Tooling Checklist == | ||
* Temperature-controlled '''soldering iron''' (fine 1 mm conical tip) | * Temperature-controlled '''soldering iron''' (fine 1 mm conical tip) | ||
* '''Desoldering wick''' 2 mm & spring pump | * '''Desoldering wick''' 2 mm & spring pump | ||
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* '''Kevlar gloves / eye protection''' for CRT section work | * '''Kevlar gloves / eye protection''' for CRT section work | ||
== | == Post-Recap Adjustments == | ||
The PET’s PSU has no trimmer; voltage is set by the transformer and 7805. | The PET’s PSU has no trimmer; voltage is set by the transformer and 7805. | ||
If +5 V is low after recapping, check: | If +5 V is low after recapping, check: | ||
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The '''monitor''' focus & vertical-height pots (_on the video board_) may drift after fresh caps—re-adjust for crisp text with a plastic tool. | The '''monitor''' focus & vertical-height pots (_on the video board_) may drift after fresh caps—re-adjust for crisp text with a plastic tool. | ||
== | == Additional Notes == | ||
* C9/C10 sometimes leak _inside_ the aluminium can and look fine externally—always meter for ESR. | * C9/C10 sometimes leak _inside_ the aluminium can and look fine externally—always meter for ESR. | ||
* Early _“blue label”_ PETs (with 6540 ROMs) omit C11; later logic boards include it—verify before ordering. | * Early _“blue label”_ PETs (with 6540 ROMs) omit C11; later logic boards include it—verify before ordering. | ||
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[[Category:Commodore Systems]] | [[Category:Commodore Systems]] | ||
[[Category:Capacitor Replacement Guides]] | [[Category:Capacitor Replacement Guides]] | ||
Latest revision as of 23:06, 1 August 2025
The first-generation PET 2001 (1977 – 1979)—assemblies 320008 / 320081 / 320132—uses a simple linear supply together with an internal 9" monochrome CRT. After forty-plus years, the original electrolytic capacitors are at (or past) their design life. Re-capping:
- stabilises the +5 V / +12 V rails used by the logic and VIC video section,
- removes vertical “jail-bars”, shimmering, or ticking noises caused by dried-out CRT filter caps, and
- protects irreplaceable ICs such as the 6502, the twin 6520/6522 PIA/VIA I/O chips, and the early mask ROM/SRAM devices.
Tip ► The PET will usually still boot with tired capacitors—but voltages sag as it warms up, causing random lock-ups and screen collapse. Fix the caps before chasing “mystery” digital faults.
Visual Inspection
[edit | edit source]- Bulging or domed tops – particularly the two large 4 700 µF smoothing cans (C9 & C10).
- Brown crust or green verdigris at the rubber bungs.
- ‘Fishy’ smell when the board warms up – electrolyte seepage.
- White salt deposits around the CRT board’s high-voltage electrolytics.
If any of the above are present, _replace the whole set_ – piecemeal swaps often lead to repeated strip-downs.
Capacitor Reference Tables
[edit | edit source]Values are taken from Commodore parts sheets parts-3.gif (system board) and parts-6.gif (video board) for the PET 2001 series. Board lettering differs slightly between early 6540/6550 “static” boards (320008) and later 2316B/2114 “dynamic” boards (320132); positions are therefore given as silkscreen “Cx” + functional description.
🔌 Main Power / Logic Board (all 2001 revisions)
[edit | edit source]| Designator | Location / Function | Capacitance | Voltage | Notes |
|---|---|---|---|---|
| C9 | 5 V rail smoothing (after bridge) | 4 700 µF | 25 V | Axial can, glue-mounted |
| C10 | 5 V rail secondary filter | 4 700 µF | 25 V | Identical to C9 |
| C11 | 12 V booster reservoir | 2 200 µF | 25 V | Generates +12 V for VIC/audio |
| C12 | 5 V pre-reg filter | 1 000 µF | 25 V | Near 7805 regulator heatsink |
| C13 / C14 | Logic decoupling bulk caps (left & right board edges) | 220 µF | 16 V | 2 pcs |
| C16 – C27 | Local bypass (scattered across DRAM/ROM rows) | 10 µF | 16 V | 12 pcs |
Use 105 °C low-ESR parts for C9–C13—they run hot next to the transformer.
CRT (Video/Deflection) Board
[edit | edit source]| Designator | Function | Capacitance | Working V | Qty |
|---|---|---|---|---|
| C101 | B+ rail reservoir | 220 µF | 200 V | 1 |
| C102 | Horizontal output stage | 100 µF | 200 V | 1 |
| C103 | Vertical sweep supply | 47 µF | 160 V | 1 |
| C108 | Video amplifier decouple | 10 µF | 50 V | 1 |
| C110 / C111 | Sync & oscillator timing | 1 µF | 160 V | 2 |
| C115 | Heater/filament filter | 100 µF | 25 V | 1 |
| C120 – C123 | Frame-store / blanking filters | 22 µF | 50 V | 4 |
Safety! C101 & C102 sit at ~160 V DC. Discharge them _with a 100 kΩ 2 W resistor_ before desoldering.
Optional Dynamic-RAM Board (PET 2001-8 upgrade)
[edit | edit source]Early 2001-8 machines add a small plug-in board carrying four 2114 SRAMs and four 10 µF / 16 V electrolytics (C201–C204). Replace these at the same time.
🛠️ Replacement Procedure
[edit | edit source]- Isolate power & remove the 2 A slo-blo fuse.
- Disassemble – take out the motherboard (4 screws) and pivot the monitor/keyboard assembly.
- Document with photos; note capacitor polarity (square pad = positive on PET PCBs).
- Desolder using braid or a spring pump. PET boards are single-sided—lifted pads are common; be gentle.
- Clean pads with isopropyl alcohol; scrape away corroded lacquer if necessary.
- Fit new capacitors; keep lead length minimal and apply fresh thermal compound to the 7805 if removed.
- Re-assemble, checking that C9/C10 do not short against the case bottom.
- Power-on with series-bulb limiter (or bench-supply) and verify rails:
- +5 V = 4.95 – 5.10 V at the 6502 (pin 8 = GND, pin 40 = Vcc)
- +12 V ≈ 11.6 – 12.6 V at VIC pin 18
- Run the PET for 30 min burn-in; touch-test that the 7805 < 65 °C and C101/C102 remain cool.
Tooling Checklist
[edit | edit source]- Temperature-controlled soldering iron (fine 1 mm conical tip)
- Desoldering wick 2 mm & spring pump
- ESR meter or capacitance tester (optional but recommended for pre-check)
- 100 kΩ / 2 W resistor lead for safe high-voltage discharge
- Non-acidic IPA (99 %) & ESD brush
- Kevlar gloves / eye protection for CRT section work
Post-Recap Adjustments
[edit | edit source]The PET’s PSU has no trimmer; voltage is set by the transformer and 7805. If +5 V is low after recapping, check:
- bridge rectifier D1–D4 for heat damage,
- continuity of the power-switch contacts, and
- correct mains-tap wiring (120 V vs 240 V).
The monitor focus & vertical-height pots (_on the video board_) may drift after fresh caps—re-adjust for crisp text with a plastic tool.
Additional Notes
[edit | edit source]- C9/C10 sometimes leak _inside_ the aluminium can and look fine externally—always meter for ESR.
- Early _“blue label”_ PETs (with 6540 ROMs) omit C11; later logic boards include it—verify before ordering.
- If you plan a modern switch-mode 5 V module in place of the 7805, you may down-rate C9/C10 to 2 200 µF 16 V low-ESR; ripple is dramatically lower.