Peavey Vyper 15w Modeling Amp only works through headphone jack

[Roshihyde]

The title pretty much sums it up I get power but even if I unhook the input jack from the pcb board I get nothing from the speaker. If I use the headphone jack for headphones or an external speaker everything works fine. I have no idea where to go from here.

[soundguruman]

The headphone jack has internal switches.
When you unplug the headphone, it's supposed to connect the speaker.
When you plug in the headphone, it disconnects the speaker.

So, probably the headphone jack is damaged. The internal switches no longer connect the speaker, when headphones are removed.
Check the solder connections to the jack, or replace the jack.

[Jazz P Bass]

Ahh, if it was oh so simple.

It's not.

When you plug into the headphone jack, it lifts the HP JACK pin off of ground. As the pin is normally pulled up to 3.3volts, it will go high at U6 pin 13. That high input gets translated by the microcontroller (U8) & it (the Uc) tells the power amp to mute.

So you may have a headphone jack problem (U6, pin 13 is always high).

Or the power amp output is always muted.
That would involve the mute circuit, which is centered around Q7 (J111).

Or it could be that the output IC is bad.

If it is a jack problem, it may be an easy fix (resolder/ replace jack)

If not the jack, you will need a high level skill set to repair this amp.