Like the previous time quoted below, thought it was a PbF problem at the
input socket, as a definite problem in that area causing about 1/10th volume
but not mains noise intrusion, when testing on receipt
PbF solder used inside but nowhere stated , as per usual. The same symptoms
appeared before and as used with a footpedal at that point, under warranty
Fender replaced the foot pedal.
Is the schematic for this digital+valve amp around ?
I cannot see how loss of ground contact and ring contact to ground would
cause a consistent (in failure) 1/10 or so volume drop. PbF solder points at
the socket (now managed to remove the preA pcb )
look good (for PbF)
No WD40 this time, input socket bush nut , not loose on receipt, same off
centre type , not desoldered yet but probably another junk Neutrik. The 2
parts of the barrel turn relative to one another ,easily , without the bush
nut in place braced against the chassis

previous experience
"
Fender Bassman 250 , PR597, 2005
Bad input socket, is there a generic problem with these?
Of course I thought it was a PbF problem but it escaped that , leaded solder
inside. Solder joints seem fine and no broken tag. Socket make not seen ,
not desoldered yet, maybe make underneath.
The jack centre line is off-centre of the socket centre line , the sleeve
contact is a barrel which is chromed and only makes contact with the now
tarnished ground contact if the metal bush nut is tight and the 4 pointed
grounding tangs are not bent and are making good contact with chassis metal.
So 2 ways of loosing ground contact. With no bush nut the chromed barrel
will rotate a few degrees and then just touching contact to the socket
ground terminal .
Of course I have the preamp out of the chassis now and so do not know what
the initial state was other than the bush nut was not loose when received.
All compounded by gallons of WD40 squirted everywhere that has certainly
lost the tip and ring bypass contacts to ground with no jack inserted.
I can see repeated tightening/ overtightening? of the metal bush nut
plenty of spanner/wrench force can be applied as metal nut and metal bush)
will deform the 4 tangs/ dig deeper pits into the front panel metal, until
eventually no contact.
I expected some no-name Chinese make but no , it is Neutrik with this crappy
design.
http://www.neutrik.co.uk/en-uk/plugs...s/nrj6hm-1-pre
http://www.neutrik.co.uk/zoolu-websi...wing+NRJ6HM-1-
PRE
Reassembled preamp with the socket exposed and it was then obvious there is
a third way to loose ground contact. There is no sprung contact to the
sleeve of the jack , just rests on the chromed barrel , relying on the
spring contacts of the tip and ring to supply pressure to keep the sleeve in
contact with the inside and innermost small segment of arc of the chromed
barrel . Even without WD40 , corrossion and general crud , because of the
lever action, it takes very little upward force on the jack, at the cable
end , to lift the sleeve and break contact.
So failure mechanism probably went like this.
Bad ground contact due to slack nut. Instead of tightening, owner squirts
WD40 in there which
pools in the lower surface of the barrel , collects crud, congeals etc.
Eventually he tightens the nut , but by then its too late.
The input was always bad from new, according to the owner, but got worse
over the years.
AFAICS no way could this design be of merchantable quality
A get by , on the
road, solution to this would probably be some sort of reaming action inside
the bush barrel
Replaced with 3 sprung contact Cliff with plastic barrel and added star
washer wired-in. You can then have
something like an interference fit between jack and barrel , so little or no
play in any off-axis direction. Because the Neutrik is metal and metal there
has to be a clearance fit and so its easy to break the sleeve contact.
Neutrik barrel internal about 6.30mm, 6.20 jack sleeve, Cliff So 6.68mm "