Marshall MG50DFX No sound

[bullius]

Hi,

So, first the channel selector stopped working. Then, I plug the guitar in and get no sound at all.

I get sound when I plug into the FX input and the CD input, but not the main input.

I have tried a little WD-40 on the input socket, but no change.

Any thoughts?

[nickb]

Something in the preamp has died. We'll need to troubleshoot. Please take look at this post - what is your score?
Also, what part of the world do you live in?

[glebert]

Get a schematic (they are out there) and post here. For the preamp if you turn the knobs for gain, treble, middle, etc, do you hear any noise out of the speaker (like white noise)? If you get some noise you can try to work backwards from the power amp input (I think labeled PAIN on the schematic, lol) you may find that some knobs affect the noise and others have no effect, or clean channel vs. overdrive. If turning a knob changes the noise out that part of the circuit is probably working.

Also, since the channel selector wasn't working before, it may be that the channel switch relay has failed or stuck in a middle state. Try hitting it hard, see if that makes a difference.

edit: I think the channel switching is a CMOS relay, so hitting it probably won't help...

[The Dude]

^^^^^^ What nickb said. What are your technical abilities? Do you have a DVM, solder iron, etc. What is your experience level? On a side note, please don't use WD-40 on electronic components. And,......welcome to the place!

[bullius]

Thanks for all the replies.

I live in the UK. nickb, I notice you are located in Devon. I am not too far from there.

My equipment/knowledge/skills are as follows:

Measurement equipment, which you have/use.
1. I do not have/use any measurement equipment.
But I can get some.

Knowledge in electronics.
In between...
1. I know nothing about electronics.
2. I’m familiar with Ohm’s law and I can read and understand electric schematics.
(It has been a long time since GCSE Electronics!)

Professional skills.
I can solder & have an soldering iron.

The schematic can be found here: https://elektrotanya.com/marshall_mg.../download.html

[nickb]

OK first get a Digital Mulimeter and then measure the DCV with respect to ground (the sleeve of the input jack is handy for the ground of the meter lead) on

IC1,2,3 & 4 on pins 4,8,1,7
IC9 pins 1,4, 8, 13.

How far away are you from Okehampton? It's recommended to add your location to your profile. It saves all the questions.