Alpine MRV-F353 Problem

[bigpun4fubu]

Ok all 5 channels work, but the sub channel has weak audio and measures 27.76 Volts DC on sub out terminals , all fets and drivers check to be ok in circuit

[Perry Babin]

Post a photo of the inside of the amp.

[bigpun4fubu]

[Perry Babin]

You stated that it has 27v DC and produces audio. Do you have a capacitor in series between the speaker and the amp or did it push the cone fully in/out when you connected the speaker?

[bigpun4fubu]

pushes the cone fully out with no signal

[Perry Babin]

When you checked the smaller transistors, did you just check to see if there were any reading 0 ohms?

You may have one leaking. Check them carefully. If one reads lower than you think it should, pull it out of the circuit and re-check it.

[bigpun4fubu]

Is the D718 transistor N-channel or P channel? and same question for B688 transistor those are the output mosfets

[Perry Babin]

Neither is N or P-channel. These aren't FETs. The D718 is an NPN. The B688 is a PNP. They are both BJTs (Bipolar Junction Transistors -- or simply bipolar transistors).

[bigpun4fubu]

both small transistors between output transistors...seem to check good checked several times and saw no leakage

[Perry Babin]

Those are the bias transistors. They rarely fail. The readings look OK.