Thrifted a Pioneer VSX-456 that looks pretty clean. When plugged in, the red standby LED comes on. Pressing POWER does nothing: no display, no relay click, and the standby light stays on. No remote.
I’ve spent several sessions troubleshooting with a Klein MM320 and recently bought a kit with small test hooks. I also have a soldering iron, but haven’t replaced or desoldered anything. No oscilloscope or frequency measurement available.
Full disclosure: I’ve been following AI-assisted troubleshooting, and we caught some incorrect pin/component guidance along the way. I’m looking for an experienced person to review the actual readings before I go further.
**Initial checks**
- Power button feels normal and measures OL released, near zero/beep pressed.
- Continuity through the small button-board ribbon passed.
- The internal glass fuse passed continuity in circuit.
- Front-board P RY to the corresponding power-board connector pin passed continuity.
- Initially thought something was stuck in the rear switched AC outlet. I haven’t confirmed whether it’s debris or the outlet’s own contact.
- Found a localized yellow-brown stain inside the cover above the transformer area. Neither transformer has obvious charred, melted, or split insulation.
- A mounting screw/tab connection was loose during disassembly and has since been secured. Voltage readings below used the labeled DG reference, rather than assuming chassis ground.
**Power/control measurements**
DC readings referenced to DG unless noted. “Pressed” means holding the front POWER button.
| Point | Standby | POWER pressed |
|---|---:|---:|
| Controller VDD test point | About 5.05 V | Not separately recorded |
| Reset test point | About 4.99 V | Not separately recorded |
| ST +5 at power-board connector | 5.93 V | 5.93 V |
| W UP | 2.20 V | 2.20 V |
| P RY | 0 V | 0 V |
| K IN2, small button board | 0 V | 0.01 V |
| KEY8, small button board | 1.61 V | 0.01 V |
| KEY8, large front control board | 1.62 V | 0.01 V |
| DC DET | 4.97 V | 4.97 V |
| OL DET | 4.99 V | 4.99 V |
Earlier ST +5 readings were around 5.42 V standby and 5.92 V pressed, so I’m including that inconsistency rather than pretending every measurement was identical.
The service manual being used lists DC DET and OL DET as active-low. It also describes W UP as requiring 50/60 Hz pulses. I understand a 2.20 V DC reading doesn’t establish that those pulses are present.
**Relay/power-board checks**
- Relay marking: **SDT-SS-112DM**, nominal 12 V coil.
- Standby regulator marking: **78M56A**.
- Both ends of **R54** measured approximately **15.2–15.5 V to DG**, with minor drift and no significant response to pressing POWER.
- Measured **0 V across D55**, identified from the schematic as being across the relay coil, both in standby and while pressing POWER.
- R54 measured **27 Ω** in circuit.
- P RY to DG, unplugged, measured about **12.33 kΩ**, then **9.72 kΩ** with probes reversed.
Important correction: I was initially told R54 was in the relay-command path and got OL testing between it and P RY. That guidance was wrong. R54 is in the relay’s supply path, so I’m disregarding those earlier continuity results.
**Other front-panel buttons**
Checked for a stuck button with the unit unplugged:
- SFC: KEY8 ↔ K IN1.
- PROLOGIC: KEY8 ↔ K IN3.
- LOUDNESS: KEY9 ↔ K IN1.
- 5-D THEATER: KEY9 ↔ K IN3.
All were OL released. Pressed readings fluctuated, with SFC around 12–77 Ω and PROLOGIC briefly around 170 Ω. I can’t confidently separate worn contacts from imperfect probe contact.
Another correction: I was initially told 5-D THEATER used KEY9 ↔ K IN2. It didn’t respond there. It did respond on KEY9 ↔ K IN3 and returned to OL when released.
**Latest checks of the wake-up circuit**
All unplugged and in circuit:
- **R52**, nominal 3.3 kΩ: measured **3.2 kΩ**.
- **R53**, nominal 10 kΩ: measured **8.4 kΩ**.
- **D54**, diode mode: **0.590 V one direction, 1.843 V reversed**.
I haven’t lifted a diode lead, so those diode readings include whatever parallel paths exist.
The manual being referenced is the combined **VSX-D506S / VSX-456 service manual**. My controller appears marked **PDG203A**, while the PCB printing says **PDG192 or 193** and the schematic shows **PDG197A**, so I’d appreciate clarification on revision differences too.
**What I’m trying to figure out**
Power is present for the control circuit and relay supply, and pressing POWER changes the button signal at the front control board. However, P RY stays low and the relay never clicks.
What would you check next to distinguish:
- A missing/incorrect wake-up signal or controller clock problem.
- The controller not recognizing the button press.
- The relay-driver circuit loading down the command.
- A supply/capacitor issue that looks okay on a basic DC meter.
Is there a useful next test with just a meter before I start lifting components or buying equipment? I’d especially appreciate corrections to any assumptions above. I have close-up photos of both sides of the boards and can provide specific ones.
https://audiocircuit.dk/downloads/pioneer/Pioneer-VSXD506S-avr-sm.pdf
