No PbF statements anywhere but I assume it is.
Reported as consistent intrusive mains hum with any settings of
controls, but of course with me it is perfect. Expecting a loose cap or
input socket problem, but nothing found. Before dismantling the amp,
anything to check , from access side only at the moment.
So far,cursory comparison, circuit looks like this one
http://www.schematicsunlimited.com/o...d/OTQ2Nw%3D%3D

On Tuesday, February 2, 2016 at 9:46:47 AM UTC-5, N_Cook wrote:
No PbF statements anywhere but I assume it is.
Reported as consistent intrusive mains hum with any settings of
controls, but of course with me it is perfect. Expecting a loose cap or
input socket problem, but nothing found. Before dismantling the amp,
anything to check , from access side only at the moment.
So far,cursory comparison, circuit looks like this one
http://www.schematicsunlimited.com/o...d/OTQ2Nw%3D%3D

Sounds like a polarity problem with the AC input. Is there are polarity switch on this unit? Floating ground?

On 02/02/2016 15:11, wrote:
On Tuesday, February 2, 2016 at 9:46:47 AM UTC-5, N_Cook wrote:
No PbF statements anywhere but I assume it is.
Reported as consistent intrusive mains hum with any settings of
controls, but of course with me it is perfect. Expecting a loose cap or
input socket problem, but nothing found. Before dismantling the amp,
anything to check , from access side only at the moment.
So far,cursory comparison, circuit looks like this one
http://www.schematicsunlimited.com/o...d/OTQ2Nw%3D%3D

Sounds like a polarity problem with the AC input. Is there are polarity switch on this unit? Floating ground?


No polarity or ground lift options. There's always a question I forget
to ask the owner. This time how prominent was the hum, like unplugging a
guitar and touching the pin of the plug, or just noticeable with no
signal through. I'll have to email, while I dismantle the amp.

On 2016-02-02, N_Cook wrote:
No PbF statements anywhere but I assume it is.
Reported as consistent intrusive mains hum with any settings of
controls, but of course with me it is perfect.

Thus, a likely hypothesis is that it is picking up some EMI in its
regular location, with the regular instrument and other signal chain
components that it is hooked into: stomp boxes, and their power
supplies, cabling.

Expecting a loose cap or
input socket problem, but nothing found. Before dismantling the amp,
anything to check , from access side only at the moment.

Step one is to reproduce the problem. Get the user to demonstrate it,
if possible. Re-create some of the original conditions, if necessary.

You can hardly be effective in investigating a problem that isn't
reproducing.

Not to mention fixing it; how can you be sure something is gone, that
you never observed!

Even if you *do* reproduce a problem, doing something that apparently
makes it go away isn't necessarily a proper fix. So far, one thing that
makes the problem go away is to relocate the amp to your polace.
See? Not a proper fix.

On 2016-02-02, wrote:
On Tuesday, February 2, 2016 at 9:46:47 AM UTC-5, N_Cook wrote:
No PbF statements anywhere but I assume it is.
Reported as consistent intrusive mains hum with any settings of
controls, but of course with me it is perfect. Expecting a loose cap or
input socket problem, but nothing found. Before dismantling the amp,
anything to check , from access side only at the moment.
So far,cursory comparison, circuit looks like this one
http://www.schematicsunlimited.com/o...d/OTQ2Nw%3D%3D

Sounds like a polarity problem with the AC input.

If it is a polarity problem, it could be in the outlet that the amp
is plugged into at home.

Kaz Kylheku wrote:


Reported as consistent intrusive mains hum with any settings of
controls, but of course with me it is perfect.


Thus, a likely hypothesis is that it is picking up some EMI in its
regular location, with the regular instrument and other signal chain
components that it is hooked into: stomp boxes, and their power
supplies, cabling.


** Long as the amp exhibits no AC frequency hum when used alone, it has no fault.



Step one is to reproduce the problem. Get the user to demonstrate it,
if possible. Re-create some of the original conditions, if necessary.
You can hardly be effective in investigating a problem that isn't
reproducing.


** Of course, but few customers are capable of comprehending even that simple idea.


Not to mention fixing it; how can you be sure something is gone, that
you never observed!


** Of course, but having outlined a perceived fault customers expect it to be fixed and never return.

Only thing is to write on the invoice:

" Fault not seen, not fixed and not warrantied "



..... Phil

Kaz Kylheku wrote:


Sounds like a polarity problem with the AC input.

If it is a polarity problem, it could be in the outlet that the amp
is plugged into at home.


** This recent British made amp uses an AC supply ground conductor so plug polarity is irrelevant.

Been a long, long time since guitar amps were sold with no safety ground.
Some mad Yankee idea, I believe.



.... Phil

Definitely PbF used, but nothing obviously wrong in the way of ring
cracks etc.
"digital" checking of caps (with fingers) a Sanwha SD, 47uF 450 V , C16
designation ,would move like that situation of pad and pin fully
soldered over so you cannot see the metal of the pin at all, but there
is movement of the cap as the pin is moving fully enclosed in a PbF
solder "socket". Ground back the solder on both pins to show
discontinuity of metals and still no movement seen. A physical break
inside the cap on one pin of 'D' anode supply to the preamp, of the R/C,
B to E HT chain. I've yet to hear back from owner , how much hum there was.

If it is a polarity problem, it could be in the outlet that the amp
is plugged into at home.



Just yesterday had a hum problem caused by the infamous "yellow glue turned
brown"

The glue was apparently conductive enough to couple to a signal lead right
at the edge of the goop.

Strangely, the hum was 60 hz instead of 120. Still haven't figured out that
part.


Mark Z.

On Friday, February 5, 2016 at 7:02:41 AM UTC-5, Mark Zacharias wrote:
If it is a polarity problem, it could be in the outlet that the amp
is plugged into at home.



Just yesterday had a hum problem caused by the infamous "yellow glue turned
brown"

The glue was apparently conductive enough to couple to a signal lead right
at the edge of the goop.

Strangely, the hum was 60 hz instead of 120. Still haven't figured out that
part.


Mark Z.

If the glue became conductive - then it would be due to a chemical salt within its composition. Many salts, by nature are diodes - so it would rectify only half the wave-form - 60 hz.

Just a random thought.

Peter Wieck
Melrose Park, PA

"Mark Zacharias" wrote in message ...

If it is a polarity problem, it could be in the outlet that the amp
is plugged into at home.



Just yesterday had a hum problem caused by the infamous "yellow glue turned
brown"

The glue was apparently conductive enough to couple to a signal lead right
at the edge of the goop.

Strangely, the hum was 60 hz instead of 120. Still haven't figured out that
part.


Mark Z.






Just today I was clearing yet another pair of KRK Rokit8 powered speakers of
black glue gone conductive.
These are not particularly old, yet this problem has been around for a very
long time.

How long does it take for manufacturers to stop using this ****?



Gareth.

On Friday, February 5, 2016 at 1:43:53 PM UTC-5, Gareth Magennis wrote:


How long does it take for manufacturers to stop using this ****?

Keep in mind that RTV silicon materials emit (contain) acetic acid (vinegar). Which attacks copper, at least. It may not be the glue itself, but the curing products reacting with the metal(s) within the system. As long as things are dry, OK. But under high humidity conditions, the salts will attract moisture, and then let the fun begin.

Peter Wieck
Melrose Park, PA

wrote in message
...

On Friday, February 5, 2016 at 1:43:53 PM UTC-5, Gareth Magennis wrote:


How long does it take for manufacturers to stop using this ****?

Keep in mind that RTV silicon materials emit (contain) acetic acid
(vinegar). Which attacks copper, at least. It may not be the glue itself,
but the curing products reacting with the metal(s) within the system. As
long as things are dry, OK. But under high humidity conditions, the salts
will attract moisture, and then let the fun begin.

Peter Wieck
Melrose Park, PA






I think the problem here is the heat generated inside a small speaker
cabinet by the power amps. I suspect it is this heat cycling that
transforms the glue into something else.


Gareth.

"Gareth Magennis" wrote in message ...



wrote in message
...

On Friday, February 5, 2016 at 1:43:53 PM UTC-5, Gareth Magennis wrote:


How long does it take for manufacturers to stop using this ****?

Keep in mind that RTV silicon materials emit (contain) acetic acid
(vinegar). Which attacks copper, at least. It may not be the glue itself,
but the curing products reacting with the metal(s) within the system. As
long as things are dry, OK. But under high humidity conditions, the salts
will attract moisture, and then let the fun begin.

Peter Wieck
Melrose Park, PA






I think the problem here is the heat generated inside a small speaker
cabinet by the power amps. I suspect it is this heat cycling that
transforms the glue into something else.


Gareth.





Could it be that some carbon compound or something else in the glue
gradually migrates to the bottom of the glue pile as it constantly softens
and rehardens?
This would place a nice conductive layer on the PCB.



Gareth.

On 05.02.16 19:43, Gareth Magennis wrote:


"Mark Zacharias" wrote in message ...

If it is a polarity problem, it could be in the outlet that the amp
is plugged into at home.



Just yesterday had a hum problem caused by the infamous "yellow glue turned
brown"

The glue was apparently conductive enough to couple to a signal lead right
at the edge of the goop.

Strangely, the hum was 60 hz instead of 120. Still haven't figured out that
part.


Mark Z.






Just today I was clearing yet another pair of KRK Rokit8 powered speakers of
black glue gone conductive.
These are not particularly old, yet this problem has been around for a very
long time.

How long does it take for manufacturers to stop using this ****?



Gareth.

They do it on purpose. It ensures failure a bit
after the guaranty period........

wrote in message
...
On Friday, February 5, 2016 at 7:02:41 AM UTC-5, Mark Zacharias wrote:
If it is a polarity problem, it could be in the outlet that the amp
is plugged into at home.



Just yesterday had a hum problem caused by the infamous "yellow glue
turned
brown"

The glue was apparently conductive enough to couple to a signal lead
right
at the edge of the goop.

Strangely, the hum was 60 hz instead of 120. Still haven't figured out
that
part.


Mark Z.

If the glue became conductive - then it would be due to a chemical salt
within its composition. Many salts, by nature are diodes - so it would
rectify only half the wave-form - 60 hz.

Just a random thought.

Peter Wieck
Melrose Park, PA


I did wonder about that but it seemed a bit much. There was also an
important but not necassarily the same circuit ground in the affected area.
Possibly that coupled over somehow.

mz

Just today I was clearing yet another pair of KRK Rokit8 powered speakers
of black glue gone conductive.
These are not particularly old, yet this problem has been around for a
very long time.

How long does it take for manufacturers to stop using this ****?



Gareth.




I don't think it's by accident.

mz

Gareth Magennis wrote:



How long does it take for manufacturers to stop using this ****?


I think the problem here is the heat generated inside a small speaker
cabinet by the power amps. I suspect it is this heat cycling that
transforms the glue into something else.


** The black glue used has the same problem as the old yellow glue - over time and with a little heat it hardens and become conductive and corrosive to metal.

Rokit8s have it poured all over the place like salad dressing and it is very tedious to fully remove and repair the damage it causes.

Users tend to leave powered speakers like KRKs or Alesis powered on 24/7 in the mistaken belief they turn off automatically when not being used - when all they do is mute. A LED indicator goes out on the front to reinforce the idea. This means the problem happens years earlier for them.

The Alesis M1s are the worst, cost the SMPS blows up and a toroidal inductor has to be stripped, cleaned & rewound.


..... Phil