Mesa 5:50 Express, no sound

[Nirvana]

Hi everyone,
Im looking for some guidance to fix my amp.
It turns on fine, both power tubes look active, pre-amp tubes 3 & 4 are lit up 1,2, & 5 are not. Red pilot light comes on but no green/red channel lights or instrument sound (pic attached)
I CAN get sound if I bypass the input jack and plug the guitar into the fx loop return (pic attached). I don't use this amp often and last time I used it, it worked just fine but suddenly it doesn’t.
A local repair guy shared his thoughts over an email quote (but who didn't want to work on it) said over an email the +12v line is at least partially working as the pilot light is turning on so it must be another component in line with the channel LED and mute circuit.
Any ideas?
Thanks guys.

[Helmholtz]

Do you get 12VDC across C48?

[Enzo]

Turn off the room lights. NOW are those unlit tubes still unlit?

[Nirvana]

Hi Helmholtz.
Im getting 0.081 V. I think....
I put a lead on each side of the capacitor, I'm far from an electronics expert so please let me know if I am taking the reading correctly.

[Nirvana]

Turn off the room lights. NOW are those unlit tubes still unlit?

Yes.

[g1]

How about DC volts across C50, on the input side of the 7812 regulator?

[Nirvana]

How about DC volts across C50, on the input side of the 7812 regulator?

Where would I put the leads at to take this reading?

[g1]

Same as you did for the other cap, one probe to each lead of cap.

[Nirvana]

Same as you did for the other cap, one probe to each lead of cap.

Do I have to take the capacitor off the board like ive read in many tutorials?

[Jazz P Bass]

No, you not need to remove the capacitor.

You are trying to determine the health of the 12Vdc supply.

By going across C 48, you are measuring the output of the 12 volt regulator.
By going across C 50, you are measuring the input to the regulator.

Note: please make sure your meter is set to read Volts DC.

[Nirvana]

No, you not need to remove the capacitor.

You are trying to determine the health of the 12Vdc supply.

By going across C 48, you are measuring the output of the 12 volt regulator.
By going across C 50, you are measuring the input to the regulator.

Note: please make sure your meter is set to read Volts DC.

Thanks for the explanation, that does help me to understand what we are looking for.
I don't have access to underneath the board so I put the multimeter leads where I think the correct place would be.

As stated before my background is Mechanical Engineering, not electrical so I do appreciate the help and patience guys.

[Nirvana]

[Nirvana]

Took another reading the next day and 0V

[Nirvana]

[Nirvana]

Whole board