# HP 3458A Outguard PSU Capacitor Replacement Board

## Sprague 53D358 → 9× Vishay MAL225090105E3

This PCB adapter replaces the original **Sprague 53D358** electrolytic capacitor on the HP/Agilent **3458A** multimeter's outguard power supply board (A6, position C8) with nine modern **Vishay MAL225090105E3** capacitors.

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## Background

The original Sprague 53D358 (8300 µF, 35 V) is a long-discontinued component that is virtually impossible to source today. Over time these capacitors dry out or fail entirely, which can cause instability or complete failure of the 3458A's outguard power supply. This replacement board allows the use of modern, readily available capacitors with comparable or better specifications.

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## Specifications

| Parameter    | Original         | Replacement (×9)       |

|------------------|---------------------------|-------------------------------|

| Part      | Sprague 53D358      | Vishay MAL225090105E3    |

| Capacitance   | 8300 µF         | 9× 1000 µF (9000 µF total) |

| Voltage rating | 35 V           | 35 V             |

| Size      | single large can     | 16 × 20 mm (each)      |

| Status     | Discontinued       | Current production      |

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## Photos

Bare PCB (1.jpg)

Assembled board with capacitors (2.jpg)

Installed in the 3458A outguard power supply (3.jpg)

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## Files

| File / Folder   | Description               |

|---------------------|------------------------------------------|

| `53d358_G.kicad_pcb` | KiCad PCB layout            |

| `53d358_G.zip    | Gerber files ready for PCB manufacturing |

| `53d358_G.jpg`   | PCB render / preview image       |

| `1.jpg`, `2.jpg`, `3.jpg` | Photos: bare PCB, assembled board, and installed in the instrument |

| `BOM.csv`      | Bill of materials            |

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## Installation

1. Desolder and remove the original Sprague 53D358 from position **C8** on the A6 outguard power supply board.

2. Clean the pads and install the adapter PCB in its place.

3. Reinstall the A6 board, ensuring the mounting pin seats correctly.