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← Repair Guides|Power Supply Capacitor Replacement (Recap)
medium90 min

Power Supply Capacitor Replacement (Recap)

Symptoms this guide addresses

  • •Unit powers on but audio is distorted or noisy
  • •Intermittent startup failures
  • •Low or unstable power rail voltages
  • •Unit works when cold but fails after warm-up
  • •Visible bulging or leaking on PSU board capacitors

Tools required

  • •Soldering iron (temperature controlled)
  • •Solder wick / desoldering pump
  • •Digital multimeter
  • •Phillips #1 screwdriver
  • •Capacitor ESR meter (optional but recommended)

Overview

The Emax power supply uses electrolytic capacitors that are now 35+ years old. Electrolytics have a finite lifespan and degrade with heat and age, causing increased ESR (equivalent series resistance), capacitance loss, and eventual leakage. A full PSU recap is strongly recommended on any unit showing instability.

Power Supply Voltages

Per the service manual, the Emax PSU should measure:

Rail Nominal Acceptable Range
+5V +5.00V +4.85V to +5.15V
+12V +12.00V +11.5V to +12.5V
-12V -12.00V -11.5V to -12.5V
+15V +15.00V +14.5V to +15.5V
-15V -15.00V -14.5V to -15.5V

Measure at the test points identified in the service manual (Section 4, Power Supply Specifications, page 26) before and after recap.

Capacitor List

The following electrolytics are on the PSU board. Replace all of them — do not spot-replace.

Ref Value Voltage Notes
C1 4700µF 25V Main filter
C2 4700µF 25V Main filter
C3 1000µF 25V
C4 1000µF 25V
C5 470µF 25V
C6 470µF 25V
C7 100µF 25V
C8 100µF 25V

Note: Verify values against the schematic on page 43 of the service manual — earlier and later revisions may differ.

Recommended Replacements

Use 105°C rated capacitors for improved longevity. Panasonic FR or Nichicon UHE series are recommended.

  • 4700µF 25V: Panasonic EEU-FR1E472 (Mouser 667-EEU-FR1E472)
  • 1000µF 25V: Panasonic EEU-FR1E102 (Mouser 667-EEU-FR1E102)
  • 470µF 25V: Panasonic EEU-FR1E471 (Mouser 667-EEU-FR1E471)
  • 100µF 25V: Panasonic EEU-FR1E101 (Mouser 667-EEU-FR1E101)

Procedure

  1. Power off and unplug. Discharge the main filter caps before touching anything — short across the cap terminals with a 1kΩ resistor.
  2. Remove the PSU board (refer to service manual Section 2 for access).
  3. Photograph the board before desoldering to record capacitor orientations.
  4. Desolder and replace caps one at a time, observing polarity.
  5. Reinstall and measure all rail voltages before connecting to the main board.
  6. Trim pots VR1–VR4 if any rail is out of spec (see service manual page 26–27).
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