Mrshall mg10

[phantom]

Hey guys, I picked up this little practice am the other day and it makes a static type noise only when the guitar cord is plugged in. I was wondering if anyone had any insight. I was scared to ask on the Marshall site, it's all tube's there.
I'm waiting on a star crunch, Promethium Distortion, and a heavy spider to build with my son.
Thanks in advance,
Dave Thomas

 

[phantom]

I forgot to say I did clean the input jack.

 

[jwin615]

Check the switch function of the jack.
With amp off, plug in a blank jack or short cable and check the resistance between tip and sleeve. It should be isolated or at least extremely high(Mohms). If using a cable, check the cable by itself(unplugged)
If it's lower, the switching function mqy be an issue. If it's good, you'll need to dive into the circuit.
But if it only makes noise with the cable plugged in, it's either the jack or ground plane issue. I'd start with checking the diodes and caps before the opamp.

 

[phantom]

Thank you for your reply. I Have checked the input jack and it is fine. I will move on to the diodes and caps.