Editing Atari 400 General Maintenance (section)

== Power Supply & Voltage Checks ==

The original Atari 400 uses an external '''9V AC linear power supply'''. Over time, these bricks can drift out of spec or fail outright.

{| class="wikitable styled-table" style="width:70%;"
! Pin/Lead !! Function !! Healthy Range
|-
| Barrel centre || 9V AC || 9.0 – 11.0 V AC (unloaded)
|-
| Barrel sleeve || Ground || 0 V
|}

* '''Test the PSU output with a multimeter''' before each use. Overvoltage or excessive ripple can damage internal regulators and logic.
* If the original PSU runs hot, buzzes, or smells of ozone, '''replace with a modern regulated supply''' (9V AC, ≥1.5A).
* Inspect the power jack for looseness or corrosion; reflow solder joints if necessary.

=== Internal Voltage Regulators ===
The Atari 400 uses onboard '''7805 (5V) and 7812 (12V) regulators'''.
* With the system powered, measure:
** '''+5V rail:''' 4.95 – 5.20 V at mainboard test points or across C111.
** '''+12V rail:''' 11.8 – 12.3 V at 7812 output or across C108.
* If voltages are low or unstable, suspect failing regulators or filter capacitors.