Would seem to be RTFM but no mention in the manual
http://data.manualslib.com/pdf3/67/6...y__fifteen.pdf
All guitar types seem to be set at 100% drive/dirtiness or whatever
distortions. Go to change them in the display and press the now red
"save" button and the display comes up "memory locked" .
Nothing in manual to say how to unlock. A forum for frustrated fenderers
has press Utility button twice but that does not work with this PR 938
flavour of amp.

What a pallaver
Long press on Util button
press rightmost cursor button until display reads "Mem Lock" for that button
Press that button again
then rotary selector knob to change display to read "off"

"N_Cook" wrote in message
...
What a pallaver
Long press on Util button
press rightmost cursor button until display reads "Mem Lock" for that
button
Press that button again
then rotary selector knob to change display to read "off"



I hate these micro-controlled bollox amplifiers with a passion. DSP
'modelling' I can just about live with, but rotary encoders for controls ?
But even worse, normal pots, connected to A-D inputs on a micro ?Virtually
every one I see has a problem that's down to finger trouble ... Just a
couple of weeks ago, I had a Vox Valvetronix combo in that said "comes on
very quiet". Well that's because it's the way you set it before saving and
switching off, you moron. RTFM, or better yet, buy an amp with just a volume
and three tone controls on it.

I currently have a 4 x 6L6 Fender in for repair that has uP controlled bias,
FFS !! What a load of utter nonsense. What on earth was the designer
thinking of, or his supervisor when he approved it ? The micro is currently
doing absolutely nothing - not even any clock present, although the 3.3
volts is present on the chip. The bias is supposed to be controlled by four
PWM signals driving transistors, but of course, as there is no clock, these
drives are missing with the result that the output grids are all at -89
volts ...

The board that this lot is all on is utterly unrepairable, with SM
components the size of gnat's cocks. We're currently trying to persuade
Fender to tell us if this board is available even, let alone its price ...
:-(

Arfa

Arfa Daily wrote:


I currently have a 4 x 6L6 Fender in for repair that has uP controlled bias,
FFS !! What a load of utter nonsense. What on earth was the designer
thinking of, or his supervisor when he approved it ? The micro is currently
doing absolutely nothing - not even any clock present, although the 3.3
volts is present on the chip. The bias is supposed to be controlled by four
PWM signals driving transistors, but of course, as there is no clock, these
drives are missing with the result that the output grids are all at -89
volts ...

The board that this lot is all on is utterly unrepairable, with SM
components the size of gnat's cocks. We're currently trying to persuade
Fender to tell us if this board is available even, let alone its price ...
:-(


** Hughes and Kettner make similar amps:

http://ru.hughes-and-kettner.com/pro...e%2050%20Combo

All the pots are just encoders for the DSP system, so every tiny movement makes an annoying click. The blurb says " ..an built-in tube technician..... "

Yep, a tiny SMD board adjusts the idle current and, if out of range, even biases off the particular valve. The trick circuit allows allows H&K to use a small toroidal output tranny - cos it keeps bias balance spot on.

Had one of the little horrors on the bench back in July, dead because the heater fuse had blown. ******* to get open and put back together too.

When running, I found it was riddled with HF oscillations under all load conditions - open, resistive and speaker load.

The output stage is a Marshall clone, but there was no cap across the 12AX7 phase splitter anodes - I found fitting 100pF fixed the oscillations.

Beware.


.... Phil

Owner just needed a simple practise amp, but ended up with this thing
that is way over the top and needs driving lessons before you can use it.
Reminded of the acoustic bass player and his Roland Cube that kept
returning to me as it distorted, but absolutely no problem that I could
find.
Eventually it emerged he just wanted a simple but small amp and speaker
for his bass and ended up with all this DSP stuff. His opinion was that
as he didn't want any of the features other than volume , he turned all
the controls anti-clockwise. That put the "type" feature into octave
bass under-imposing an octive under his acoustic bass, hence the
observed "distortion"

"Phil Allison" wrote in message
...
Arfa Daily wrote:


I currently have a 4 x 6L6 Fender in for repair that has uP controlled
bias,
FFS !! What a load of utter nonsense. What on earth was the designer
thinking of, or his supervisor when he approved it ? The micro is
currently
doing absolutely nothing - not even any clock present, although the 3.3
volts is present on the chip. The bias is supposed to be controlled by
four
PWM signals driving transistors, but of course, as there is no clock,
these
drives are missing with the result that the output grids are all at -89
volts ...

The board that this lot is all on is utterly unrepairable, with SM
components the size of gnat's cocks. We're currently trying to persuade
Fender to tell us if this board is available even, let alone its price
...
:-(


** Hughes and Kettner make similar amps:

http://ru.hughes-and-kettner.com/pro...e%2050%20Combo

All the pots are just encoders for the DSP system, so every tiny movement
makes an annoying click. The blurb says " ..an built-in tube
technician..... "

Yep, a tiny SMD board adjusts the idle current and, if out of range, even
biases off the particular valve. The trick circuit allows allows H&K to
use a small toroidal output tranny - cos it keeps bias balance spot on.

Had one of the little horrors on the bench back in July, dead because the
heater fuse had blown. ******* to get open and put back together too.

When running, I found it was riddled with HF oscillations under all load
conditions - open, resistive and speaker load.

The output stage is a Marshall clone, but there was no cap across the
12AX7 phase splitter anodes - I found fitting 100pF fixed the
oscillations.

Beware.


... Phil


Thanks for the tip, Phil. Noted. I'm guessing that this fender is supposed
to keep the bias balance just so as well, as it has low value resistors in
the output cathodes, with the voltage across them fed back to A-D inputs on
the micro as far as I can see. Except of course that there is no feedback
volts a the moment because with - 89v on the grids, the valves are into
really hard cut-off.

I'm at a bit of a loss to see what the supposed advantage is on this
particular design, which uses a perfectly conventional EI cored output
tranny. Unless the valves have gone really badly out of balance - in which
case they probably need replacing anyway - I would defy most users to be
able to hear any difference ... :-)

Arfa

, Arfa Daily wrote:

"Phil Allison"



Thanks for the tip, Phil. Noted. I'm guessing that this fender is supposed
to keep the bias balance just so as well, as it has low value resistors in
the output cathodes, with the voltage across them fed back to A-D inputs on
the micro as far as I can see. Except of course that there is no feedback
volts a the moment because with - 89v on the grids, the valves are into
really hard cut-off.

I'm at a bit of a loss to see what the supposed advantage is on this
particular design, which uses a perfectly conventional EI cored output
tranny. Unless the valves have gone really badly out of balance - in which
case they probably need replacing anyway - I would defy most users to be
able to hear any difference ... :-)


** Is your Fender a " Super Sonic Twin " by any chance ?

Real dog apparently.

http://www.ultimate-guitar.com/revie...win/index.html

Sounds like their auto bias board is near identical to the one in the H&K.



..... Phil

"Phil Allison" wrote in message
...
, Arfa Daily wrote:

"Phil Allison"



Thanks for the tip, Phil. Noted. I'm guessing that this fender is
supposed
to keep the bias balance just so as well, as it has low value resistors
in
the output cathodes, with the voltage across them fed back to A-D inputs
on
the micro as far as I can see. Except of course that there is no feedback
volts a the moment because with - 89v on the grids, the valves are into
really hard cut-off.

I'm at a bit of a loss to see what the supposed advantage is on this
particular design, which uses a perfectly conventional EI cored output
tranny. Unless the valves have gone really badly out of balance - in
which
case they probably need replacing anyway - I would defy most users to be
able to hear any difference ... :-)


** Is your Fender a " Super Sonic Twin " by any chance ?

It's actually a Supersonic 100 head, but same chassis in a small
speaker-free cab, I believe Phil



Real dog apparently.

http://www.ultimate-guitar.com/revie...win/index.html

Sounds like their auto bias board is near identical to the one in the H&K.

Haven't come across the HK one so can't comment, but might well be. This one
actually says Fender on it, but they might be trading the design around
amongst themselves. It also has three preset 'settings' for soft, normal and
hard bias, accessed via a foil switchpad, and a toggle switch for 'club' and
'arena' modes. Personally, if they must have user bias settings, I would
prefer three preset pots inside, and a three way switch. I really don't
believe that output valve balancing is enough of an issue to warrant this
kind of complexity. On amps that have a bias balance preset, you have to set
it a long way off before you can hear much effect, and even then, it's
usually only a slight increase in background hum level ...

Arfa



.... Phil

Arfa Daily wrote:

"Phil Allison"

Sounds like their auto bias board is near identical to the one in the H&K.

Haven't come across the HK one so can't comment, but might well be. This one
actually says Fender on it, but they might be trading the design around
amongst themselves.

** Or just copying each others efforts.

It also has three preset 'settings' for soft, normal and
hard bias, accessed via a foil switchpad, and a toggle switch for 'club' and
'arena' modes. Personally, if they must have user bias settings, I would
prefer three preset pots inside, and a three way switch.


** Having users actually tweak valve bias pots is a bad idea - but having an automatic system with user selectable criteria is fine.


I really don't
believe that output valve balancing is enough of an issue to warrant this
kind of complexity. On amps that have a bias balance preset, you have to set
it a long way off before you can hear much effect, and even then, it's
usually only a slight increase in background hum level ...


** On many Fender models (egs 135W twin and Super Twin) you can set the bias balance by monitoring the residual 100Hz hum at the output. But if that means a setting way off centre the valves are bad.

Read the blurbs I posted, the auto bias system is there to allow the user to change valves from old to new or from one brand to another and know the bias will be correct. Going from NOS RCA 6L6GCs to Russian 6L6wxts or 5881s and Chinese made KT66s etc with no need to see a tech is a big selling feature.

That H&K model even allows the user to change from EL34s to 6L6s.

However, the system cannot cope with faulty valves and may even be damaged by them OR fail totally like you found. Also, it is sometimes possible to put an octal valve in the socket out of key or having broken the spigot install it any position you like. Results are often dramatic.

IME having guitar players fool around putting valves in their amps is full of traps & hazards - owners are bound to fall into one sooner or later.


..... Phil

















Arfa



.... Phil

"Phil Allison" wrote in message
...
Arfa Daily wrote:

"Phil Allison"

Sounds like their auto bias board is near identical to the one in the
H&K.

Haven't come across the HK one so can't comment, but might well be. This
one
actually says Fender on it, but they might be trading the design around
amongst themselves.

** Or just copying each others efforts.

It also has three preset 'settings' for soft, normal and
hard bias, accessed via a foil switchpad, and a toggle switch for 'club'
and
'arena' modes. Personally, if they must have user bias settings, I would
prefer three preset pots inside, and a three way switch.


** Having users actually tweak valve bias pots is a bad idea - but having
an automatic system with user selectable criteria is fine.


I really don't
believe that output valve balancing is enough of an issue to warrant this
kind of complexity. On amps that have a bias balance preset, you have to
set
it a long way off before you can hear much effect, and even then, it's
usually only a slight increase in background hum level ...


** On many Fender models (egs 135W twin and Super Twin) you can set the
bias balance by monitoring the residual 100Hz hum at the output. But if
that means a setting way off centre the valves are bad.

Read the blurbs I posted, the auto bias system is there to allow the user
to change valves from old to new or from one brand to another and know the
bias will be correct. Going from NOS RCA 6L6GCs to Russian 6L6wxts or
5881s and Chinese made KT66s etc with no need to see a tech is a big
selling feature.

That H&K model even allows the user to change from EL34s to 6L6s.

However, the system cannot cope with faulty valves and may even be damaged
by them OR fail totally like you found. Also, it is sometimes possible to
put an octal valve in the socket out of key or having broken the spigot
install it any position you like. Results are often dramatic.

IME having guitar players fool around putting valves in their amps is full
of traps & hazards - owners are bound to fall into one sooner or later.


.... Phil

Fully agreed

Arfa

Bit of a result. Finally got a reply from Fender's service department. The
nice man asked how old it was. We told him about three years and he said
they'd had a batch of ones from about that time that had caused issues, so
he is sending us one, from stock.

Arfa