Hummingbird Avant Garde - Electrics problem

[atosoup]

HI all, Looking for some advice.

I have a Gibson Hummingbird Rosewood Avant Garde, Its only 18 months old but its developed a weird problem.  When I plug it into my Marshall JCM or my small ( Cheap) practice amp I get no sound at all from the amp,, I get a slight crackle when moving the volume knob on the guitar,,, But whats weird is if I plug it into my Yamaha THX mini amp I have sound , and it sounds great ( Volume knob still crackles when I move it a little,, )  BUt then If I plug my pedalboard between the Yamaha amp and the guitar I have no sound at all again,,  This is a problem that has just started happening as It all worked beautifully before..   the problem is 100% with the guitar and not the gear as I have many other guitars I have tested the setup with,

I have also tried 2 new different 9v battery's that have made no difference.

Please can anyone help?

[Twang Gang]

Sounds like it may be a short in the guitar's output jack.  Not working at all and then working again with a different amp.  Seems like something is loose and  works sometimes but cuts out all together at other times.

[75 Hummingbird]

Have you switched out the patch cord ?