Commodore 64 Power-Supply Protector (C64 Saver)
| |
| Caption | A popular open-hardware implementation of the C64 Saver |
|---|---|
| Type | External over-voltage / over-current protection adapter |
| Designer | Ray Carlsen (original design) community derivatives (OpenC64Saver, SaV64, SaRuMan-64, C64 Saver 2, etc.) |
| Manufacturer | Unknown |
| First released | 2016 (public release of the Carlsen “C64 Saver 1.2” design) |
| Latest revision | C64 Saver 2.4 PCB (2022) |
| Operating voltage | +5 V DC (monitored) • 9 VAC passthrough |
| Layers / PCB | — |
| Compatibility | Commodore 64 / 64C / SX-64 / VIC-20 CR and any CBM 8-bit that uses the 7-pin DIN power connector |
| Features | — |
| Model No. | — |
The Commodore 64 Power-Supply Protector—best-known by Ray Carlsen’s original name “C64 Saver”—is a small plug-through safety adapter that sits between a vintage Commodore power brick and the computer.
Its only mission is to sacrifice itself if the +5 V rail from the ageing “epoxy-potted” supply drifts above a safe level, instantly disconnecting the load and saving irreplaceable MOS chips such as the VIC-II, SID, CIA and RAM.
Why a Protector Is Needed
[edit | edit source]Original Commodore “brick” PSUs were cost-reduced, epoxy-potted switchers with no serviceable parts or active regulation feedback. With age the internal linear regulator or crowbar diode can short, driving the +5 V DC rail to 7–12 V—high enough to destroy ICs within seconds. Modern collectors therefore avoid the stock PSU unless a C64 Saver-class device is in-line.
Operating Principle
[edit | edit source]| Function block | Component example | Description |
|---|---|---|
| Over-voltage sense | TL431 programmable shunt (earlier boards use 5 V zener) | Monitors the 5 V rail; trips at 5.3–5.5 V (adjustable ± 50 mV). |
| Crowbar / latch | SCR (e.g. C106D) or P-channel MOSFET + relay | When tripped, shorts the rail through the SCR or mechanically opens the circuit; resets only when input power is removed. |
| Fuse element | Resettable polyfuse 1.1 A or fast-blow 1 A | Limits fault current so the PSU shuts down instead of the computer. |
| Visual alert | Bi-colour LED | Green = normal; Red = tripped/over-voltage. |
| Passthrough lines | 9 VAC pair, Sense line | These are not switched—protector covers only +5 V DC. |
- OpenC64Saver* introduces reverse-polarity protection, replaces the SCR with a low-RDS(on) MOSFET for cooler running, and adds a precision trim-pot for exact trip voltage set-up.
Design Evolution
[edit | edit source]| Variant | Year | Key features | Trip point (nom.) |
|---|---|---|---|
| C64 Saver 1.x (Ray Carlsen) | 2016 | Through-hole, SCR crowbar, 5 V6 zener | 5.4 V |
| C64 Saver 2.x (RC) | 2019 | Smaller PCB, TL431 reference, polyfuse replaces wire link | 5.25 V |
| OpenC64Saver (SukkoPera) | 2018 | Fully open hardware, MOSFET disconnect, reverse-polarity diode | User-set |
| SaV64 / SaV64-II (SharewarePlus) | 2019 | Commercial kit, optional OLED volt-meter, user-replaceable fuse | 5.25 V |
| SaRuMan-64 | 2020 | SMD, auto-reset, fold-back current limit | 5.30 V |
All variants honour Carlsen’s open-distribution request that the design remain non-proprietary for the benefit of the community.
Typical Bill of Materials (through-hole C64 Saver 2.3)
[edit | edit source]| Qty. | Reference | Part |
|---|---|---|
| 1 | F1 | Polyfuse 1.1 A (RXE110) |
| 1 | SCR1 | C106-D or BT151-500R |
| 1 | U1 | TL431 (2 %) shunt reg |
| 2 | R1, R2 | 1 kΩ & 4.7 kΩ (trip divider) |
| 1 | R3 | 220 Ω (LED limiter) |
| 1 | C1 | 100 nF decouple |
| 1 | D1 | 1N4148 (gate clamp) |
| 1 | D2 | 5.6 V Zener (reference bias) |
| 1 | LED1 | 3 mm bi-colour (GRN/RED) |
| 1 | J1 | Male 7-pin DIN (to PSU) |
| 1 | J2 | Female 7-pin DIN (to computer) |
Installation
[edit | edit source]- Power off and unplug the PSU.
- Connect the PSU’s 7-pin DIN plug into the male side of the Saver.
- Plug the Saver’s female 7-pin into the computer.
- Power up. LED should show green.
- If LED immediately turns red or no power reaches the C64, the PSU is already faulty—do not keep using it.
The device draws under 5 mA and introduces ≈ 15 mΩ series resistance, insignificant even for sensitive Ultimate-64 boards.
Testing the Trip Circuit (Bench)
[edit | edit source]- Dial a bench supply to 5.0 V and feed the Saver through the DIN pins (+5 V → pin 2, GND → pin 5).
- Increase voltage slowly; at 5.3–5.5 V the LED flips to red and the output collapses to ≈ 0 V.
- Remove input power for 5 s to reset the latch.
Limitations
[edit | edit source]- Does not regulate ripple—a PSU with excessive 50/60 Hz ripple under 5.2 V will still pass.
- No 9 VAC protection; an internal short in the PSU transformer can still inject noise or excessive VAC.
- Not a substitute for a modern PSU—it is a last-line “crowbar”, not continuous regulation.
- If the SCR version trips it may blow the PSU’s internal fuse; replace that fuse before re-testing.
Where to Buy or Build
[edit | edit source]- DIY PCB/gerbers: OpenC64Saver repository (KiCad + BOM).
- Kits / assembled: SharewarePlus SaV64 series, RETRO Innovations, and many eBay/Tindie sellers.
- Integrated solutions: All Ray Carlsen modern PSUs ship with an internal Saver circuit plus precision linear regulation.
Related Pages
[edit | edit source]- Commodore 64 Power Supply Guide – failure modes of the original bricks
- Commodore 64 Capacitor Replacement Guide
- Commodore 64 Troubleshooting Guide