PL700II Hum/Buzz volume control issue

[RadioMan]

2nd photo, the upper green cap, left lead beside solder joint. Is that a break? Probably not, but that's only thing I see. Very nice clean unit.

It looks like a break in the photo but it fine.
I went a reflowed all the connections on the rear of the unit and still no luck?

 

[George S.]

Set pots mid point and start probing with a scope?

 

[RadioMan]

I think I may experiment with lead dress and move the audio wires away from the power wires and see what happens.

BTW where can I get a replacement power switch for a 4000II preamp?

 

[Gepetto]

I think I may experiment with lead dress and move the audio wires away from the power wires and see what happens.

BTW where can I get a replacement power switch for a 4000II preamp?

You have the usual PL ground loop central going on inside that amp.

 

[RadioMan]

You have the usual PL ground loop central going on inside that amp.

What have been the solutions for this in the past?

 

[Hexis22]

What have been the solutions for this in the past?

Sorry for being a smart ass (kind of), but the solution is a full WOPL upgrade.

 

[RadioMan]

Sorry for being a smart ass (kind of), but the solution is a full WOPL upgrade.

No offence taken I kinda agree.

 

[RadioMan]

I have fixed some of the Carver magnetic field stuff in the past but never worked on a PL400/500/700 before.

What I will say is this looks like a “Fly By The Seat Of Pants” amp design. What I see is a design that uses the least amount of parts possible to deliver good sound but the design has many flaws and seems like it’s on the edge blowing up if you just look at it funny.

After working on this amp I can see why a WOPL conversion is the way to go.

I think I would rather have an old Peavey amp than a PL700.

At this point I think I will just run the amp with pots full open and leave the amp alone before it blows up with me poking around. Works good, Sounds good, Done.

 

[George S.]

If

BTW where can I get a replacement power switch for a 4000II preamp?

Don't know about the 4000 S2, but the 2000 S1 and S2 have a extra set of unused contacts on the switch.

 

[Gepetto]

What have been the solutions for this in the past?

Removing the buss wire between the speaker grounds and the switch ground to chassis, removing the copper input plate connection to that same chassis ground point. Ensuring that the ground for the control board comes from the copper buss between the bulk caps.