john l wrote:I read 100k from all the lugs on the presence pot to the chassis. I then set my meter for continuety and am getting a steady beep from the back of the pot to the chassis.
That's likely the problem then. 100K is your feedback resistor. Depending on which model it is, one leg of the pot should be grounded to the pot housing, or connected to ground through a separate 4K7 resistor. Either way, you shouldn't read more than about 5K from any leg to ground.
Its a 1987 lead spec. Which way are those wired? With or without the 4.7k? What value is the pot suppost to be?
The 1987 Lead MkII has a 5K pot with the left and center lugs tied (one lead of the presence cap connects there). There should be a 4K7 resistor to ground from the right leg. Probably removed accidentally when the shielded wire was added. You don't have to do it that way; the basic 1987 model (and most other Marshalls just ground the left lug, put the cap on the center (other end grounded) and connect only the feedback to the right lug.) The lead model is a little brighter because the presence is always at least halfway "on."
Reeltarded wrote:Pres pot! Back of pot. Left leg (up orientation) is ground, center is cap, cap to ground (back of pot) right leg purple wire to 100k nfb resistor on board.
I see you have a white wire coming out of the -side of the board for the presence, but I see your presence wire disappears in an odd way up the board, and it looks like someone used shielded wire on the pot to wherever it terminates now. Where does that wire terminate?
That .68 on the pres pot is supposed to be center lug and grounded to the back of that pot.
DONE DEAL, wiring it up as you said did it! I dont have a 4.7 on yet but that jumpered from the right lug with an aligator clip to ground and the cap on the center lug did the trick.
Thankyou guys so much!! I had all kinds of horrible thoughts swiming around in my brain lol. The only 4.7k I had on hand was a giant 2 watt Carbon Comp so its a bit funny looking for the time being but it sounds great and now I know that theres nothing wrong with my favorite amp which is huge for me. I really cant tell you guys how much I appreciate your help. Im sure that would have ran me a couple hundred bucks if I had to pass it on to someone more capbable.
