Yamaha A-S2100 Stuck In Protection

[Soundscape]

IC504 : + or - Voltage matters

Pin 4 : input VDD = +5.8V
Pin 3 : Vout = +5.0V
Pin 2 : ground = assuming near 0V
Pin 1 : chip enable = F if I know, lol

 

[mbz]

the voltages I collected are: 5.22V, 4.42V, 4.44V, and around 4mV

5.22V as input is on the low side(5.8V), causing a lower than expected 4.4V output, spec is 4.95 to 5.05. IC504 is fed from IC506 check Vin(10V) on IC506. Also test R656 (1P/10ohms) possibly drifted high, test in circuit initially

 

[mbz]

Pin 1 : chip enable = F if I know, lol

Just allows for microprocessor (or other) control.
Chip is enabled since we are getting an output, Vin is skinny, need to look upstream

 

[Soundscape]

Slowly getting my head around the schematic.

I'd scratch the idea of faulty opto-couplers as this would cause a PSVA1 error. Monitoring voltage at R339 would confirm, note one side is GND, wanting otherside of R339 to be +0.6Vdc abouts, ie, Q304 = ON

For PSVA2 candidates are Q303,2,1 D309, D310, these are SMD and mounted on the SMD side of the board so difficult access. The unit does not appear to have a removeable base plate so would need to remove the MAIN(3) board = major PITA. Looking for +4.4Vdc at diode anodes and +3.8V at cathodes

Pardon my manners on this one mbz...I fast forwarded to the regulators for ease of troubleshooting since Q303,2,1, are a buried PITA.

 

[mbz]

No issue, other input always welcome, looks like you are onto something, the +5S rail is low, plz continue

 

[Soundscape]

IC506 pin out Jones: FYI OP

 

[Soundscape]

OP...I hope you're using non destructive test probes. I prefer testing from CB's or wire connectors before the components to cause no harm. Notice the connector where the IC506 +10V goes. Up to you though. Mbz mentioned R656. I'd test both sides of that resistor live and compare voltage drop.