Schematic — A20112 Power Supply

If you have a specific A20112 variant or an unusual failure, post clear photos of both sides of the PCB on electronics repair forums – with the knowledge from this guide, the community will help you map out the exact schematic.

Test the main bridge rectifier diodes and any feedback Zener diodes using your multimeter’s diode check function.

, most notably used in certain boutique or smaller tube amplifiers like those from or similar custom builds.

| Symptom | Likely Fault (per schematic) | Diagnostic Step | |---------|-------------------------------|-----------------| | No output, fuse blown | Shorted MOSFET (Q1) or bridge rectifier | Check diode mode across drain-source of MOSFET. Replace both MOSFET and current sense resistor. | | Output cycles on/off (ticking sound) | Overcurrent protection active | Check secondary Schottky diode (short) or output capacitor (high ESR). Measure CS pin voltage – should be <1V. | | Output present but drops under load | Failed bulk capacitor (C5, 400V) | The capacitance drops below 50µF. Replace with 105°C rated Lelon or Nichicon. | | Very low output (e.g., 3V) | TL431 or optocoupler failure | Temporarily disconnect optocoupler; if output jumps high, FB loop is the issue. | | No standby power, but fuse OK | Startup resistor (R2, 1MΩ) open or VCC capacitor (C13, 47µF 50V) dried out | Check R2 resistance; replace C13. | a20112 power supply schematic

The 2011 power supply schematic appears to be a switching-mode power supply (SMPS) design, which is a popular topology for high-efficiency power conversion. The schematic consists of several key components, including:

A high-performance SMPS tracking the R2A20112 architecture relies on a series of specialized electronic stages to transform raw AC utility lines into stable DC voltage.

Here is the block-level breakdown of the : If you have a specific A20112 variant or

Absorbs high-voltage spikes and transient surges from the main power grid.

Measure across the input and output rails with a multimeter. Check for direct shorts to ground before applying power.

4.3 DC-DC Regulation — Flyback (isolated) reference | Symptom | Likely Fault (per schematic) |

Stability & debugging checklist

The controls power MOSFETs to "shape" the current, ensuring it stays in phase with the voltage.

Below are detailed functional descriptions and reference circuit suggestions. For clarity, two reference implementations are described: A) Isolated flyback (mains input), B) Non-isolated synchronous buck (DC input).

If your unit has stopped working or is cutting out, users frequently report issues with the output transformer blown screen resistors