Repair: Sega power block (candy cab)¶
The switch-mode PSU of Sega candy cabs (Astro City, New Astro City, Blast City…). It supplies the JAMMA rails: +5 V, +12 V, −5 V. Key points: the +5 V adjustment (to compensate for harness losses) and the recap as it ages.
Identification¶
| Field | Value |
|---|---|
| Type | Switch-mode power supply |
| Outputs | +5 V, +12 V, −5 V (JAMMA rails) |
| Cabinets | Astro City, New Astro City, Blast City, Net City… |
| Adjustment | +5 V pot (adjustable) |
The JAMMA rails & their role¶
| Rail | Use | Note |
|---|---|---|
| +5 V | logic (CPU, ROM, RAM, TTL) | the most critical: high current, sensitive to voltage drop → adjust at the JAMMA edge |
| +12 V | audio (amp), motors/feedback, some lighting | wider tolerance |
| −5 V | analog sound of some old PCBs (DAC/filters) | often the first stage to fail; unused on many games but essential to a few |
| GND | common ground | several JAMMA pins in parallel (current) |
100 V (Japan) mains input
Japanese candy cabs are wired for 100 V. On 230 V (France), you need a step-down transformer upstream — otherwise the PSU and monitor are out of spec. Check the PSU's input range before connecting.
The +5 V adjustment (important)¶
Adjust the +5 V AT THE JAMMA EDGE, not at the PSU
The harness drops voltage. Adjust the pot to read ~5.0-5.1 V at the JAMMA connector (where the PCB sees it), not at the PSU output. Too low → crashes/ corrupted graphics; too high (>5.25 V) → risk to the board. Measure under load (board connected).
Common faults¶
| Symptom | Likely cause | Lead |
|---|---|---|
| No output / can't start | Dried-out capacitors, protection, fuse | Recap; check the fuse |
| +5 V too low / unstable | Caps, pot, harness | Recap; adjust +5 V at the JAMMA edge |
| −5 V rail absent | −5 V stage (often the first to fail) | −5 V stage diagnosis |
| Noise / hum | Filter caps | Recap |
| Hot cut-outs | Cold joints, caps | Reflow + recap |
Recap¶
An aging switch-mode PSU = recap (primary and secondary filter caps, low ESR, 105 °C). Photograph before removal (polarity). The exact list depends on the PSU model — see the Arcade Otaku PSU guide (New Astro City): https://wiki.arcadeotaku.com/w/Sega_New_Astro_City
Mains
A switch-mode PSU handles mains and holds charged capacitors. Unplug, discharge, don't work live unless you know what you're doing.
Modernisation (alternative to recapping)¶
Many restorers replace the aging original PSU with a modern industrial block (like a MeanWell), more reliable and regulated:
- A modern +5 V / +12 V PSU (e.g. MeanWell RT-65B or a dual block) + a small −5 V converter (or a DC/DC) if the game needs it.
- Advantages: stable regulation, short-circuit/overvoltage protection, silence.
- Keeping the old recapped PSU as a backup remains a good preservation practice.
Don't forget the −5 V
Generic 5/12 V supplies have no −5 V. If a game depends on it (sound), plan a dedicated module, otherwise no sound / distorted sound.
Pitfalls¶
- Adjusting the +5 V unloaded (no board) → it drops once loaded.
- Forgetting the −5 V rail (some old games need it for sound).
Photos / assets¶
(To add: Sega PSU, +5 V pot, output connectors, caps area.)
Sources & attribution¶
- Arcade Otaku Wiki — Sega New Astro City (PSUs guide) — https://wiki.arcadeotaku.com/w/Sega_New_Astro_City
- Console5 / community — candy cab PSU recap — to reference
Review & corrections
How this space is used
Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.
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