TJ's Audiophile Repair Field Notes — Master Reference

# Audiophile Repair Knowledge — TJ's Field Notes > This is the stuff I've learned fixing high-end audio gear. > Some from my years at PS Audio, some from repair benches, > some from conversations with the best techs I know. ## 1. Power / Hum / Buzz — The Most Common Call I Get ### Subwoofer Hum with Class D Amps This one took me forever to figure out. Customer has a class D amp (Stellar S300, for example) connected to a REL sub, and there's a loud hum even with the system OFF. Ground lift doesn't work. Floating ground doesn't work. Chassis ground doesn't work. **What actually works:** An unused RCA cable as a ground reference, or a chassis screw near the XLR jack. REL even used to send resistor kits for this. I sent a few of those myself. ### Power Plant Fuse Specs (From My Own Notes) - P20 220-240v: 5A, 250V, Slow-blow, 5x20mm - P20 120v: 6.3A, 250V, Slow-blow, 5x20mm - Don't deviate from the OEM rating. I've seen too many blown PSUs from people thinking "one size up is safer." ### Ground Loop Quick Diagnostic 1. Try a different grounded outlet first 2. Cheater plug — for DIAGNOSTIC ONLY, never as a permanent fix 3. Disconnect coax (cable TV ground is a notorious hum source) 4. Test with WiFi (kill the Ethernet — ground loops travel through network cables too) 5. Separate audio and power cable runs ## 2. DAC and Digital Component Repairs ### DirectStream USB Dropout Symptom is always the same: plays fine for anywhere from 5 seconds to 2 hours, then audio stops. Only fix is unplugging and re-plugging the USB. **What I learned:** This was a macOS Catalina driver incompatibility. The fix was either a digital board replacement or a firmware-side workaround that I'd send to customers directly. If your customer has this issue, start with the driver/OS compatibility before blaming the hardware. ### PWD MKII Firmware Brick Recovery Wrong firmware flashed, stuck on "Initializing," SD card won't flash. I used to handle these personally. The fix is a custom recovery SD card image from PS Audio support, then flashing firmware 3.0.4 from scratch. Don't try to shortcut this — the bootloader is picky about which cards it reads. ### DSD MK2 Aftermarket Mods — Watch Out I've seen units come back from third-party mods that were completely unrepairable. Transformer mods especially — they cause the unit to fail nearly every bench test. If a customer brings in a modified unit, let them know upfront: factory service may not be possible anymore. ### Out-of-Warranty Repair Expectations It's NOT a flat fee. Depends on age and parts availability. Vintage units (15-20+ years) cost more because parts are harder to find. Paul once asked me to look at pricing to make sure we were being fair to the HiFi Family values. ## 3. Vintage Gear and Speaker Restoration ### Speaker Foam Rot This is inevitable. Every speaker over 10-15 years old will need a re-foam. Don't patch it — replace the whole surround. Re-foam kits are cheap and restore them to factory spec. I've done this on everything from Advents to JBLs. ### Crossover Capacitors Those original electrolytics in the crossover? They've drifted. Maybe 20%, maybe 50%. Replace them with film caps of the same value. The speaker will sound like it did when it was new — sometimes better. ### Turntable Speed Issues Nine times out of ten, it's the motor capacitor. That old wax/paper cap dried out years ago. Replace with a modern film cap of the same uF rating. On belt-drive tables, also check the belt — they stretch and slip over time. On idler-drive, check the idler wheel for hardening. ### Turntable Hum Check the ground wire from the tonearm base. It's almost always a broken or disconnected ground. Next check: the cartridge ground strap. After that: phono stage issue. ## 4. Streaming and Network Audio ### Bridge II — Tidal/Qobuz Issues The MConnect app can be finicky. If it says "device does not support TIDAL," the fix is: use MConnect CONTROL (not HD), update Bridge II firmware to latest, sign

# Audiophile Repair Knowledge — TJ's Field Notes > This is the stuff I've learned fixing high-end audio gear. > Some from my years at PS Audio, some from repair benches, > some from conversations with the best techs I know. ## 1. Power / Hum / Buzz — The Most Common Call I Get ### Subwoofer Hum with Class D Amps This one took me forever to figure out. Customer has a class D amp (Stellar S300, for example) connected to a REL sub, and there's a loud hum even with the system OFF. Ground lift doesn't work. Floating ground doesn't work. Chassis ground doesn't work. **What actually works:** An unused RCA cable as a ground reference, or a chassis screw near the XLR jack. REL even used to send resistor kits for this. I sent a few of those myself. ### Power Plant Fuse Specs (From My Own Notes) - P20 220-240v: 5A, 250V, Slow-blow, 5x20mm - P20 120v: 6.3A, 250V, Slow-blow, 5x20mm - Don't deviate from the OEM rating. I've seen too many blown PSUs from people thinking "one size up is safer." ### Ground Loop Quick Diagnostic 1. Try a different grounded outlet first 2. Cheater plug — for DIAGNOSTIC ONLY, never as a permanent fix 3. Disconnect coax (cable TV ground is a notorious hum source) 4. Test with WiFi (kill the Ethernet — ground loops travel through network cables too) 5. Separate audio and power cable runs ## 2. DAC and Digital Component Repairs ### DirectStream USB Dropout Symptom is always the same: plays fine for anywhere from 5 seconds to 2 hours, then audio stops. Only fix is unplugging and re-plugging the USB. **What I learned:** This was a macOS Catalina driver incompatibility. The fix was either a digital board replacement or a firmware-side workaround that I'd send to customers directly. If your customer has this issue, start with the driver/OS compatibility before blaming the hardware. ### PWD MKII Firmware Brick Recovery Wrong firmware flashed, stuck on "Initializing," SD card won't flash. I used to handle these personally. The fix is a custom recovery SD card image from PS Audio support, then flashing firmware 3.0.4 from scratch. Don't try to shortcut this — the bootloader is picky about which cards it reads. ### DSD MK2 Aftermarket Mods — Watch Out I've seen units come back from third-party mods that were completely unrepairable. Transformer mods especially — they cause the unit to fail nearly every bench test. If a customer brings in a modified unit, let them know upfront: factory service may not be possible anymore. ### Out-of-Warranty Repair Expectations It's NOT a flat fee. Depends on age and parts availability. Vintage units (15-20+ years) cost more because parts are harder to find. Paul once asked me to look at pricing to make sure we were being fair to the HiFi Family values. ## 3. Vintage Gear and Speaker Restoration ### Speaker Foam Rot This is inevitable. Every speaker over 10-15 years old will need a re-foam. Don't patch it — replace the whole surround. Re-foam kits are cheap and restore them to factory spec. I've done this on everything from Advents to JBLs. ### Crossover Capacitors Those original electrolytics in the crossover? They've drifted. Maybe 20%, maybe 50%. Replace them with film caps of the same value. The speaker will sound like it did when it was new — sometimes better. ### Turntable Speed Issues Nine times out of ten, it's the motor capacitor. That old wax/paper cap dried out years ago. Replace with a modern film cap of the same uF rating. On belt-drive tables, also check the belt — they stretch and slip over time. On idler-drive, check the idler wheel for hardening. ### Turntable Hum Check the ground wire from the tonearm base. It's almost always a broken or disconnected ground. Next check: the cartridge ground strap. After that: phono stage issue. ## 4. Streaming and Network Audio ### Bridge II — Tidal/Qobuz Issues The MConnect app can be finicky. If it says "device does not support TIDAL," the fix is: use MConnect CONTROL (not HD), update Bridge II firmware to latest, sign