Str-de425 when turned on shows hall light only , when I opened it I noticed no power is going into the transformer ( the big one ), so I manually connected wire straight to it. If I connect it after I turn the power on it will stay flashing "protect" , if I connect it before turning it on it will power on as if normally but only A or B speaker buttons can be set to ON at a time and the speakers will play ( only A or B set ), but this one part, pc2581v IC will get too warm for no apparent reason. Should I try replacing that part ?

SOURCE: STR-DE475 receiver flashes "PROTECT" when turned on

Protection is usually a sign of overheating or something is wrong at the power amplifier's output.

Theory: Protection is a delay and sometimes an internal test to allow the electronics to stabilize during power up before they are allowed to interact with the speakers. The most common cause of it remaining ON is that a speaker cable pair is shorted. Some isolation is required...

1. Turn the Power OFF.
2. Disconnect each set of the speaker wires that are directly attached to the receiver. Mark them so you remember where each one went. pay special attention to which conductor is on "+" or "POS" and which is on "-", "COM" or "Ground". You may elect to disconnect them one pair at a time if your sytem is complex and you don't want to lose track of where things were.

Turn the Power ON. Is the "Protect" indication gone from the display?
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If YES, you have a shorted speaker wire or speaker. To isolate the specific cause:

1. Turn the Power OFF.
2. Attach ONE speaker wire pair at a time and test it by turning the Receiver ON. When the "Protect" light returns you have isolated at least one of the cause(s). Disconnect the defective speaker cable and continue isolation of all speaker cables. Visually examine the cable at both ends for frayed wires that could touch each other or contact metal on the receiver or other objects.

To isolate further within the cable/speaker pair - disconnect the speaker end of the cable on the failing path. Try another cable that you know works, or at least one that doesn't cause Protection to stay on.

If you're electrically savvy and have a Digital Volt/Ohm Meter you can troubleshoot the short(s) with it.
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If NO, there is probably an internal problem.

Is it solid or does it come on after the Receiver has been ON awhile.
It could be overheating.
Is the unit hot to the touch?
Is there a cooling device (fan)?
Is it stopped or clogged with dust?
Is there adequate ventilation around the unit for air to flow?
Clean any ventilation slots on the top and bottom of the unit.
Avoid stacking components that produce heat under an amplifier or receiver. Their heat rises. Also keep them away from other heat sources like like home heating vents and radiators.

Problem solid and NOT related to the speakers or heat: internal malfunction.

Let me know.

SOURCE: Sony's STR-DE675 5.1 Channel Receiver - Speaker OFF problem

There's a button that turns the speakers OFF right above the headphone jack.

Get the manual: retrevo.com

Testimonial: "@dunnbiker Very true on assumptions! I've tried everything the manual suggests. Right now, nothing is connected to the unit, but upon power up, I get the SP:OFF display (which is not seen in the DEMO mode). I will try the headphone jiggling idea and see what happens."