thanks Roly and Enzo.   I failed to mention in my original post that i sprayed the pot with some deoxit.  that didn't seem to do the trick.

i went ahead and removed the pot from the pcb.   the pot is disassembled, sprayed with deoxit.   i'll put things back together the next day and see how things are. 

thanks for the help.

just picked up a used mg30cfx.   great sounding for a mess around amp.......when the volume stays put, that is.   it seems that the volume on this thing wants to gradually fade out.   

I notice when the volume fades, I can touch the vol pot (there's also a master vol pot - not that one) and the volume jumps back to it's current level based on the position of the pot wiper.   the volume issue happens regardless of playing the amp through the speaker or the headphones.

I did a visual inspection of the inside, the pcb connections/joints seem to be solid; nothing loose.    for certainty, I  re-wet the solder on the vol pot jugs.  still no go.   I then went ahead and sucked up the old solder on the pot and applied some new solder, making new connections.  continutity test with my meter are good, but still a no go a properly functioning vol pot.

I tried sourcing a new oem vol pot (linear 10k ohm), but it seems like they're hard to come by (as far as oem).     the pot has three lugs up front and two at the side/rear.  the rear lugs look like they might just be there for physical support of the pot when mounted to the pcb.

I may have to find a "good enough" replacement for the pot, or see if i can salvage the existing pot first.   actually, i may do this first.   if i can fix it, great.   if i wreck the pot, well....it's already malfunctioning.  again, something in the pot is touchy.

any other/better recommendations on my approach to fixing this is greatly appreciated.

by any chance, does anyone have the schematic for the mg30cfx?   i sent an email request to marshall this morning for a copy, but i'll have to wait and see if they can help.

anyways, thanks in advance for any suggestions.


EDIT:  no go on the schematic from Marshall.   Apparently, schematics are only given to authorized service centers.    This is why i like Peavey and Fender.   Great support model.   I guess I'll try to rig something up in order to salvage this little mg.   No more Marshall for me though.  Support is lacking in my opinion.

The connector pad is repaired.  Thanks for all the input/help guys.

Enzo - you were right on with the 1/8" rivet. 

Quote from: J M Fahey on March 25, 2014, 01:49:36 PM
Fully agree with Enzo and add 1 small detail:
that silver rivet you must remove, maybe iron , or even if aluminum, the drill tip may (will) bite the iron speaker frame.
In any case you will be making small iron filings which will magnetically jump straight to the worst possible place, the voice coil gap.
Yes, *there is* a treated cloth piece in the middle .... but it's porous and the tiniest junk in the VC gap will make a mess.
So go slow, stick a crushed newspaper ball to "the other side" of the hole you are drilling with some masking tape , the idea is to catch any iron filings .
Carefully remove the paper ball, clean surfaces with a piece of tape.
After that, yes, use a Pop rivet or bolt and nut, but cover it afterwards with glue or nail enamel, the idea is for it to never self unscrew under vibration.

Thanks J M for the sometimes overlooked details.  I hadn't thought about the removal of the old rivet portion just yet, so I'm glad you beat me to it.  I would have ended up asking another question about it or not, and learned the hard way.   Thanks again.  I really appreciate the heads-up.    :tu:

I did end up picking up an Arrow rivet "toolkit" earlier today (attachment below).



I'll have to eyeball rivet size I'll be using, once I open up the package.   At first glance, looks like the 3/16" rivet may be the right fit.   

Quote from: Enzo on March 24, 2014, 11:43:21 PM
Just above the dangling terminal strip on your photos, you can see the silver rivet that held it in place.  The rivet head has pulled through the hole on the fiber board terminal strip.   You will want to remove the old rivet.   Between cutting it off and drilling it out, you should be able to remove it.  Then you can mount the strip back where it came from with a new pop-rivet or screw and nut.   Make sure the washer used with the pop rivet does not short the terminals together.

A screw could be used, but the speaker is a high vibration environment, so if the screw is your only choice, I would select a "nylock" nut.   That is a brand name for a nylon locking nut. a regular nut with an added band of plastic around the thread hole to grip the screw threads and prevent the threads from moving.

Fahey makes speakers, so if he shows up he can tell you where I went wrong here.

Thanks for the details Enzo.   Just saw a youtube vid on how the pop rivets are installed.  Pretty neat.  I'll grab some rivets in the next day or two and see how I do.

Thanks again.  Much appreciated.

~Darren

Cool and extremely helpful/insightful site this is.  My first post  :dbtu:

Problem:

I'm in the process of repairing a princeton chorus amp.  Both speakers in this amp had their wiring plate (correct terminology?) fall off.    Any advice on how I should go about affixing these plates back onto the speaker for a more permanent solution?   I attempted using a tad bit of Krazy Glue which didn't work (i anticipated this).  Solder maybe?  More hardcore adhesive (recommendations?)?  Pics attached.

Thanks in advance.

~Darren