Help needed... 2:Ninety Hum+Crackling sound

[Fl7x]

Hi guys...

I have a weird problem with my Mesa 2:90 Version 1 (Blue Pilot). It does a loud hum and intermintent crackling sound once I turn the Stand-By OFF no matter I turn the volume full up or completely off, well, the hum changes slightly but no one (the hum or the crackling) desappear. When the Stand-By is ON it's dead silent as it should to be.

To isolate the problem no preamp or any other unit is connected, just the Power-Amp.

Looking at the back I see the outter power tubes "pulsing" at the same time the crackling sound appears. I've swapped those tubes but the problem persists.

If I connect the Triaxis and engage any mode (Deep, 1/2 drive, Modern) the front LEDs on the 2:90 that shows which mode is ON "pulses" at the same time as the power-tubes and the crackling sound.

No fuse blowing, it was working perfectly 'till today.

Any thoughts?? Maybe a cold solder joint? The 12AX7 tubes? A short Circuit? I haven't checked the guts yet.

Thanks In Advance

 

[elvis]

That sounds bizarre. I would be looking for something that affects all the systems that would cause those symptoms. Maybe the power tranny or rectifier.

 

[crane]

This could the power tranny's connector attached to the board. Try remove it, use some deoxit or similar to clean the connectors then replace it.

 

[Fl7x]

It's fixed

One 12AX7 caused a short circuit between the motherboard and the filaments. The effect went through the switching circuit (the transistors that controls the DEEP, 1/2 Drive and MODERN modes).

The tech changed the faulty components, and tested the whole thing. Now runs flawless.

Trannys and other components are in perfect shape.

Thanks for your replies.

 

[elvis]

Weird. Glad it's fixed!