Peavey 6505+ no tone controls on clean & doesn't switch to crunch.

[InDecember]

Bought a used 6505+ head at a very low price, seller claimed it had no issues, so yeah sure enough it has.

Clean channel: EQ controls nor PRE gain make any difference to the tone/volume. Signal is just clean guitar tone. POST gain works.
Switching to crunch channel doesn't work (I hear the relay switching but tone remains clean).
Bright switch doesn't work.
So it's like the entire preampsection (apart from post gain) is bypassed.

Lead Channel: EQ/PRE/POST work, all good.

Everything looks nice and clean inside, no burn marks or anything. Any idea where to start looking?

[Dave H]

Schematic - Peavey-6505PLUS-112-Schematic.pdf

[InDecember]

Schematic - [ATTACH]n955292[/ATTACH]

I believe the 6505+ head is the same as the 5150II and share the same schematic:

https://www.thetubestore.com/lib/the...-Schematic.pdf

[Enzo]

6505+ is same amp as 5150-2 65505+ 112 is a different amp/circuit.

[g1]

If the mid pot (VR3) loses it's ground, none of the tone pots will work. Bright switch (SW1C) and pre (VR1) also rely on grounds to work. Maybe they all 3 connect somewhere and go through a jumper wire with bad solder or something.
Or they could be bad/dirty parts, or maybe the unit has been modified.

[The Dude]

Do all of the tube filaments light?