Sansui QRX-7500 — Vincent Long

Date: October 28, 2025 • Status: Major Electronics Restoration Completed — Awaiting Lamp Replacement
Technician: Kevin Nielsen — K-Tronix Electronics Repair

Overview

Restored full, clean audio on all front channels following capacitor, transistor, and regulator work.
Tone boards F-1484 (Left & Right) had degraded electrolytics, including a failed 1 µF / 50 V cap that caused left-channel distortion via the bass control.
Replaced all electrolytic capacitors on both tone boards and all polar electrolytics on power-supply board F-1515 with 105 °C low-ESR Nichicon/Panasonic audio-grade parts.
Left all non-polar (bi-polar) capacitors original for longevity and value stability.
Replaced mismatched power-supply regulator transistors at TR03 / TR04 with TIP41C (Onsemi) for improved rail regulation and thermal margin.
Bias and DC offset reset and balanced on all channels; left channel was significantly out of range prior to correction.
Verified tone accuracy, output symmetry, and thermal stability after extended runtime testing.

Parts Replaced

Tone Control Boards (F-1484 × 2)

Type	Typical Value	Voltage	Qty (per board)	Notes
Electrolytic capacitors	1 µF – 47 µF	16 V – 50 V	14	Nichicon UFW/UPW audio-grade
Transistors	Small-signal	—	8 (4 NPN + 4 PNP)	Replaced with 2SC1815 (NPN) / 2SA1015 (PNP) low-noise pairs

Power Supply Board (F-1515)

Ref	Value	Voltage	Type / Replacement
C01 – C29 (selected)	Various µF	10–80 V	Polar electrolytics (Nichicon / Panasonic, 105 °C low-ESR)
TR03 / TR04	2SD313 (E,F)	NPN	Replaced with TIP41C (Onsemi) regulator pair

Calibration & Testing

Bias and DC offset adjusted and verified on all channels.
Power-supply rails confirmed stable (< 2% ripple under load).
Tone and filter functions tested across full range with zero distortion.
One-hour thermal soak confirmed steady bias and current draw.

Labor & Parts Summary

Tone Boards F-1484 (L + R) — Complete Recap & Transistor Upgrade	$290.00
Power Supply Board F-1515 — Electrolytic Recap & TIP41C Regulator Replacement	$150.00
Bias / DC Offset Calibration & Thermal Verification	$40.00
Bench fee discount	$-89.00
Total Service — Electronics Restoration (bench fee removed)	$391.00

Next Step

Order and install replacement lamps to complete full front-panel illumination. Estimated parts + labor: $45–$75 (depending on lamp type and sourcing).

Service Notes

TR03/TR04 replaced with TIP41C (100 V / 6 A / 65 W), same TO-220 pinout as 2SD313.
All new capacitors are Panasonic/Nichicon, low-impedance, long-life audio grade; polarity verified, ESR/µF checked prior to install.
Audio and power sections tested post-recap for noise, stability, and thermal behavior.

Complete List of Capacitors Replaced

(Tone Boards × 2 + Power Board F-1515)

    1 µF (×6)  • 
    10 µF (×4)  • 
    47 µF 16 V (×10)  • 
    47 µF 50 V (×4)  • 
    33 µF (×4)  • 
    100 µF (×8)  • 
    330 µF (×3)  • 
    470 µF (×1)  • 
    1000 µF (×1)  • 
    0.47 µF (×1)
    Total Electrolytics Replaced: ≈ 42 capacitors across all boards.

Payment Information

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