VH4 sound to no sound problem

[bronz79]

Hi,my 2008 VH4 in the last 45 days ago has a strange problem that in 45 days happened 3 times.
The problem is this: when i switch from stand-by to run i hear no sound on ch1 and only a little
distortion on ch3/4.
It is very variable..but always happens in the warming up minutes.
Once i had no sound..once i got sound but after few seconds it slowly fades away..appears and
then disappears.
To test it i've plugged out all my effects and went straight in VH4..tested also with different guitars,
the only thing that i haven't tested is the speaker cable.

next week I'll go with the ampli to my tech.

Any ideas?

 

[Simop]

Any ideas?

Preamp tubes.

 

[bronz79]

Any ideas?

Preamp tubes.

The same idea that i have..the final stage is running and i can hear hiss increasing
by turning up master volume...only without guitar sound.

 

[duesentrieb]

Plug guitar into serial return and crank the master: please report your results

 

[bronz79]

Plug guitar into serial return and crank the master: please report your results

I can't do it now because i left today my vh4 to my tech...but if i think:
serial return is like power amp in.In true serial return plugging the guitar in
i should hear nothing out of my speaker i suppose.