Hi, I also have been looking for a schematic for Marshall 30W Master Lead Combo.... the one with no headphone or output jack. Has gain/preamp, master, treble,mid, bass, and presence. 12" speaker. It's hard to find even a photo of the model I have. I purchased in 1985.
I recently opened it up to address a scratchy volume pot and decided to take some photos while I had it open... I came across something I have not seen before. Hoping someone can enlighten me as to why it would be this way.
What I thought was a capacitor in the middle tone pot area of the pcb only has one lead attached thru the hole in the board. It seems that it was just clipped after being attached. I have attached a foto. Does this seem right?
Any ideas why?
I'm going to trace the complete board in the near future and will post for anyone who's interested.

Seems I do not have access to the attachments function so I can't post the images... hmmm.

Thanks!