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Fender deLuxe , PR772, 2009, Mexico

N

N_Cook

Jan 1, 1970
0
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-jacks/slim-jacks/nrj6hm-1-pre
http://www.neutrik.co.uk/zoolu-website/media/document/2864/Drawing+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 "
 
N

N_Cook

Jan 1, 1970
0
Seems to have cured the problem again, just wish I knew exactly how and why.
Will have to wait until a PR772 circuit emerges out there, the input line
goes off simply to a TL072 but there is compexity around the ground lines
and chassis
 
N

N_Cook

Jan 1, 1970
0
KISS, replaced the "Dyson" over-designed Neutrik with a plain and simple
Cliff .25 inch socket of which the design and materials have been around for
40 years or so.
The previous Fender Bassman never bounced back so this cure must have worked
on that occassion.
No one else come across problems with these Neutrik sockets?
 
N

N_Cook

Jan 1, 1970
0
Arfa Daily said:
Just ask Fender for a schematic. They are very helpful and will send you one
for anything that's not already available for download on their website -
which almost everything that they've ever made already is. Last week, I
needed a schematic for a "Deluxe 85". This is not on their website (UK or
US) and the only one 'out there' is with a site that wants you to pay them.
I emailed support on the US site around lunchtime here, and by late
afternoon - presumably as they opened up shop a few hours behind us - I had
a reply back from a friendly engineer called Bryce, with a copy of the
schematic attached.

Arfa

I'll try that.
There is a ground/ quasi-ground?/switching? line that goes off via a ribbon
to the PA somewhere, removing the PreA board was enough to be getting on
with , without added intellectual exercise removing the PA board just to
see where that line went
 
N

N_Cook

Jan 1, 1970
0
Arfa Daily said:
Just ask Fender for a schematic. They are very helpful and will send you one
for anything that's not already available for download on their website -
which almost everything that they've ever made already is. Last week, I
needed a schematic for a "Deluxe 85". This is not on their website (UK or
US) and the only one 'out there' is with a site that wants you to pay them.
I emailed support on the US site around lunchtime here, and by late
afternoon - presumably as they opened up shop a few hours behind us - I had
a reply back from a friendly engineer called Bryce, with a copy of the
schematic attached.

Arfa

I wasted 1/4 hour wading through the bloatware on fender.com trying to find
the em address.
Then 10 seconds googling with search-term

technical support email site:fender.com

found the em.
A Matt this time has forwarded me the schema
 
N

N_Cook

Jan 1, 1970
0
The only mechanism I can see for this 1/10 volume throughput.
The Neutrik design flaw inside the ground/barrel section, whereby tight bush
nut but the 4 sharp tangs have produced pits that then get aluminium oxide
coatings from the chassis metal or tinpest build up at the loose part inside
the barrel section. Say it builds up to 5K ohm resistance , then loss of
ring contact and so instead of say 500 ohm of a pickup it is now 5K5
presented to the input of the amp and attenuated signal current
 
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