xtian 7/30/2018 10:07 AM
Fender Jazz King / Steel King hum
I have a solid state 2004 Fender Jazz-King on the bench. Same guts as the Steel King, schematic attached. It developed a bad hum, and owner brought it to me. Hum is audible with all controls at zero, worsens when Master is turned up, and gets really bad when Reverb is turned up, even with tank disconnected.

There is only a very small DC offset at output (6mA). There is very low AC ripple (about 36mA AC) on main 57v rails.

Voltages all measure close to spec, though appear a little unbalanced. Example, TP14 = 1.15vDC, TP16 = -1.17vDC.

There do not appear to be any intermittent contacts (chopsticking produces no change in sound).

Any ideas for further investigation?

xtian 7/30/2018 10:18 AM
Well, yeah. This is a "never mind," because the hum is gone. I must have jogged something back into place. No idea what the issue was, but it's gone, and amp sounds fine.
nevetslab 8/2/2018 10:17 PM
....until the next time.
Randall 8/2/2018 11:03 PM
I would not trust that outcome one bit.