Power supplies in cabinets

How a cabinet turns mains into DC +5 V / +12 V / −5 V for the PCB, monitor, audio and lighting. Overview of the PSU types, the mains → DC rails chain, the adjustment and the safety. For hands-on teardown/recap of a Sega block: candy cab PSU repair.

Mains → (step-down transformer for 100 V cabs) → switch/fuse/filter/earth → switching PSU → +5/+12/−5 V rails → distribution.

The rails and their role

Rail	Use	Note
+5 V	logic (CPU, ROM, RAM, TTL), I/O inputs	most critical: high current, drop-sensitive → adjust at the edge
+12 V	audio amp, motors / force feedback, lamps, lit start, coin mech	wider tolerance
−5 V	analog audio of some old PCBs (DAC/filters)	often unused, but essential for a few games; first stage to fail
+3.3 V	modern boards / arcade PCs (via ATX)	absent from classic candy cabs
GND	common ground	several pins in parallel (+5 V return current)

Power-supply types

Type	Where	Outputs	Notes
Sega/Taito "candy" PSU	Astro/Blast/Egret…	+5 V, +12 V, −5 V	dedicated switcher, +5 V trimpot → repair
Generic arcade PSU ("switcher")	JAMMA cabs, superguns	+5 V (10–16 A typ.), +12 V, sometimes −5 V	the common blue/green brick; 110/220 V input (often a selector)
ATX PSU (PC)	Type X, Vewlix, Lindbergh, RingEdge…	+3.3 / +5 / +12 / −12 V	the game is a PC → standard PC PSU; the JVS I/O keeps its own feed
High-power / three-phase PSU	motion cabs (R360, deluxe)	logic + motors	high power, safety systems critical (see R360)
Linear PSU (transformer)	old cabinets	+5 V, +12 V	heavy, big transformer + rectifier + regulator; period-correct

The mains chain (input)

1. Mains: 230 V (EU), 120 V (US), 100 V (Japan).
2. Step-down transformer: required for a 100 V Japanese cabinet on 230 V → step-down (ideally isolated). Some cabs have an internal multi-voltage transformer to set to the right tap.
3. Main switch + fuse + EMI filter + earth (chassis bonded to earth — safety).
4. PSU block: rectifies and switches to the DC rails.

Earth and mains — safety

The metal chassis must be bonded to earth. Never run a cabinet without earth. The transformer primary and PSU input are at mains potential (lethal); unplug and let the capacitors discharge before any work. On a 100 V cab, an isolated step-down is recommended.

On Sega candy cabs the AC also runs through AMP Universal MATE-N-LOK connectors (same family as the DC). "AC Input" (15-pin) feeds mains into the PSU; "AC Output" (9-pin) redistributes it (monitor, accessories):

"AC Input" after GameSX/NFG — ⚡ pins at mains potential.

"AC Output" after GameSX/NFG — Live and Neutral doubled up.

Adjusting +5 V (important)

Set +5 V AT THE EDGE (JAMMA/JVS), not at the PSU output

The harness drops voltage. Adjust the trimpot to read ~5.0 V where the board sees it (JAMMA edge or JVS I/O input), under load (game connected). Too low → crashes / corrupted sprites; too high (> 5.25 V) → risk to the PCB. Higher-end PSUs have remote sense that compensates the drop automatically.

DC distribution

On Sega candy cabs (Astro/Blast/Net City, Naomi Universal) the PSU output leaves on an 18-pin "Primary DC" connector of the AMP Universal MATE-N-LOK family (3×6 matrix). It carries the +5 V / +12 V / −5 V rails, grounds, the Service line, a Test point and the speaker return (audio comes out of the PSU):

"Primary DC" pinout after GameSX/NFG — pin 1 marked by the key.

Reminder

It is a keyed connector: no risk of reversal, but check the voltages with a meter before plugging a PCB (see Adjusting +5 V).

A 12-pin "Secondary DC" (same family, 3×4 matrix) sometimes supplements the distribution — essentially doubled +5 V with GND, plus one +12 V pin:

"Secondary DC" after GameSX/NFG — pin 1 marked by the key.

• Star or daisy chain to: the JAMMA edge (PCB), the JVS I/O board (+5/+12 V), the monitor (often powered separately from 100/120 V AC), marquee/lamps/lit start (+12 V), the coin mech (counter, lockout).
• Wire gauge: +5 V draws the most current → adequate wire and several GND pins in parallel (as the JAMMA pinout provides).
• Common ground: the same ground must tie PSU, PCB and panel (see the control panel's daisy-chained ground).

Common faults

Symptom	Likely cause	Lead
Nothing powers up	fuse, switch, transformer, PSU input	Check fuse + mains present at the PSU
Crashes / corrupted graphics	+5 V too low (harness drop)	Adjust +5 V at the edge under load
No / weak sound	+12 V (amp) or −5 V (analog)	Measure 12 V and −5 V
PCB burns out	+5 V too high (> 5.25 V)	Recheck the adjustment, drifting trimpot
Unstable voltages	tired output capacitors	Recap the PSU → repair
Hum / noise	missing earth, no common ground	Check earth + common ground

See also

• Sega candy cab PSU repair — recap, adjustment, faults.
• JAMMA wiring — the power pins (+5/+12/−5 V, GND).
• JVS wiring — I/O board JST NH power.
• Sega R360 — a high-power motion cabinet case.

→ Repair: Sega candy PSU · Recap · PCB fault-finding.

Sources & attribution

• Arcade Otaku Wiki — candy cab PSUs, 100 V input, +5 V adjustment — https://wiki.arcadeotaku.com/w/JAMMA
• JAMMA standard — +5/+12/−5 V rails, GND — https://wiki.arcadeotaku.com/w/JAMMA
• NFG Games / GameSX — Sega City cabinet pinouts (18-pin Primary DC, AMP Universal MATE-N-LOK) — https://gamesx.com/wiki/doku.php?id=arcade:sega_city_cabinet_pinouts
• Internal pages: Sega PSU repair · JAMMA wiring · JVS wiring

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