Topics

549 transformer question


Joel B Walker
 

I have a very nice 549 that I have owned for nearly 35 years. It worked flawlessly at first, but then began showing the infamous epoxy HV transformer potting issue. Back when it started doing this ('87-'88) I had never heard of the epoxy problem before. I replaced the 6GE5, tested and subbed caps and diodes in the circuit to no avail. Of course the screen voltage on the 6GE5 was rising way over spec. so I knew it was being overworked. Spraying the Transformer with freeze mist would bring everything back to normal temporarily so finally decided the transformer must be bad.
In the last few years I have been reading about everyone's troubles with this same problem on many Tek scopes. I know Chuck Harris had been winding these in the past but has stopped. So the dreaded question is; Is he going to start back or is someone else going to start, is there a new solution, or are we all SOL?


greenboxmaven
 

Has anyone ever tried grinding and carving the epoxy encapsulation down to a very thin layer on the winding to see if the leakage would be reduced? The work would require skill and patience to avoid damaging the winding, getting it X-rayed before staring would help. Is the epoxy transparent enough that the winding could be seen once you were close to it without going too far? I have wondered if the conductivety goes all the way through the epoxy, or if it is just below the surface.

Bruce Gentry, KA2IVY

On 1/25/21 15:12, Joel B Walker wrote:
I have a very nice 549 that I have owned for nearly 35 years. It worked flawlessly at first, but then began showing the infamous epoxy HV transformer potting issue. Back when it started doing this ('87-'88) I had never heard of the epoxy problem before. I replaced the 6GE5, tested and subbed caps and diodes in the circuit to no avail. Of course the screen voltage on the 6GE5 was rising way over spec. so I knew it was being overworked. Spraying the Transformer with freeze mist would bring everything back to normal temporarily so finally decided the transformer must be bad.
In the last few years I have been reading about everyone's troubles with this same problem on many Tek scopes. I know Chuck Harris had been winding these in the past but has stopped. So the dreaded question is; Is he going to start back or is someone else going to start, is there a new solution, or are we all SOL?





Joel B Walker
 

There was someone in another thread who had a 567 I think with the same problem. His particular transformer had a softer rubbery encapsulation that he was able to carefully remove. From what I read in that thread, it was working at the time. I don't remember what my encapsulation consisted of. I'll have to open it up and see.


Joel B Walker
 

Sorry, I meant 667.


Joel B Walker
 

Crap! I'll get it right sooner or later. 647


Chuck Harris
 

I am working on it. I have an automated winder designed
and implemented... I still have some problems with wind
quality to resolve.

I use a micro-stepped stepper motor to directly drive the
former upon which the transformer is wound. The problem
is that even though it is micro-stepped 32x, the vibration
of the micro-steps damages the insulation on the wire...
leaving tiny creases every micro-step. The creases are
certain to be points of damage in the insulation integrity,
and are bound to cause arc-overs.

I am working on the problem from two ends, and hopefully
can solve it soon.

The winds the new machine makes are simply beautiful otherwise.

I hesitate to give any predictions, as I have been working
on this winding machine for 7-8 years. Life keeps getting
in the way.

-Chuck Harris

Joel B Walker wrote:

I have a very nice 549 that I have owned for nearly 35 years. It worked flawlessly at first, but then began showing the infamous epoxy HV transformer potting issue. Back when it started doing this ('87-'88) I had never heard of the epoxy problem before. I replaced the 6GE5, tested and subbed caps and diodes in the circuit to no avail. Of course the screen voltage on the 6GE5 was rising way over spec. so I knew it was being overworked. Spraying the Transformer with freeze mist would bring everything back to normal temporarily so finally decided the transformer must be bad.
In the last few years I have been reading about everyone's troubles with this same problem on many Tek scopes. I know Chuck Harris had been winding these in the past but has stopped. So the dreaded question is; Is he going to start back or is someone else going to start, is there a new solution, or are we all SOL?






Chuck Harris
 

The epoxy is a thin varnish that is vacuum impregnated into the windings.

The only repair I can imagine would involve repairing the broken chemistry
of the epoxy compound they used. I doubt it is possible without StarTrek
technology.

You cannot repair it... only rewind it.

-ChucK Harris

greenboxmaven via groups.io wrote:

Has anyone ever tried grinding and carving the epoxy encapsulation down to a very
thin layer on the winding to see if the leakage would be reduced? The work would
require skill and patience to avoid damaging the winding, getting it X-rayed before
staring would help. Is the epoxy transparent enough that the winding could be seen
once you were close to it without going too far? I have wondered if the conductivety
goes all the way through the epoxy, or if it is just below the surface.

        Bruce Gentry, KA2IVY


Chuck Harris
 

The 567 transformer is epoxy varnished, and then encapsulated
in clear silicone rubber, in the hope that it would prevent
moisture infiltration... It doesn't. Moisture is a symptom,
not the cause. Failed epoxy is the cause.

-Chuck Harris

Joel B Walker wrote:

There was someone in another thread who had a 567 I think with the same problem. His particular transformer had a softer rubbery encapsulation that he was able to carefully remove. From what I read in that thread, it was working at the time. I don't remember what my encapsulation consisted of. I'll have to open it up and see.






Chuck Harris
 

The 647 transformer is potted in the same brown epoxy
that failed when they just varnished the winding.

It fails just as fast as the 547 and 545B transformers.

-Chuck Harris

Joel B Walker wrote:

Crap! I'll get it right sooner or later. 647






Jim Ford
 

Say, Chuck, I worked with steppers and DC brushless motors briefly in the early 2000's at wirebonder manufacturer Orthodyne Electronics.  One project was a sinusoidal drive card to smooth out the bumps.  I understand that sine drives are available on the open market now.  We were rolling our own back then to save money because these wasn't enough competition to drive the price down.  Maybe a sine drive would help?   Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chuck Harris <cfharris@erols.com> Date: 1/25/21 1:49 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 549 transformer question I am working on it.  I have an automated winder designedand implemented... I still have some problems with windquality to resolve.I use a micro-stepped stepper motor to directly drive theformer upon which the transformer is wound.  The problemis that even though it is micro-stepped 32x, the vibrationof the micro-steps damages the insulation on the wire...leaving tiny creases every micro-step.  The creases arecertain to be points of damage in the insulation integrity,and are bound to cause arc-overs.I am working on the problem from two ends, and hopefullycan solve it soon.The winds the new machine makes are simply beautiful otherwise.I hesitate to give any predictions, as I have been workingon this winding machine for 7-8 years.  Life keeps gettingin the way.-Chuck HarrisJoel B Walker wrote:> I have a very nice 549 that I have owned for nearly 35 years. It worked flawlessly at first, but then began showing the infamous epoxy HV transformer potting issue. Back when it started doing this ('87-'88) I had never heard of the epoxy problem before. I replaced the 6GE5, tested and subbed caps and diodes in the circuit to no avail. Of course the screen voltage on the 6GE5 was rising way over spec. so I knew it was being overworked. Spraying the Transformer with freeze mist would bring everything back to normal temporarily so finally decided the transformer must be bad. > In the last few years I have been reading about everyone's troubles with this same problem on many Tek scopes. I know Chuck Harris had been winding these in the past but has stopped. So the dreaded question is; Is he going to start back or is someone else going to start, is there a new solution, or are we all SOL?> > > > > >


Michael W. Lynch
 

On Mon, Jan 25, 2021 at 03:49 PM, Chuck Harris wrote:


I use a micro-stepped stepper motor to directly drive the
former upon which the transformer is wound. The problem
is that even though it is micro-stepped 32x,
Chuck,

What stepper driver are you using? I found in my 3D printing, that using some of the more modern stepper drivers that are now available can help smooth and quiet the stepper motors. Perhaps the TMC22080 or another TRINAMIC driver could help eliminate this problem? Most of the newer drivers offer 256 native micro stepping as well as other advantages.
--
Michael Lynch
Dardanelle, AR


Chuck Harris
 

There has to be a variable ratiometric connection between the motor
that drives the transformer's former, and the motor that drives
the stylus in a back and forth motion.

The machine I made sees the transformer's winding as being
a picture drawn on a long spool of paper wrapped around the coil
former.

I create the winding by calculating the rotation angle, and
the stylus position based on the wire diameter, and the current
circumference of the coil. I feed the winder machine G-codes.

I think steppers are the way to go, but I am looking into
using a damper on the drive for the coil former. Tektronix did this
on their 4663 flatbed plotter, to cure the same problem.

-Chuck Harris

Jim Ford wrote:

Say, Chuck, I worked with steppers and DC brushless motors briefly in the early 2000's at wirebonder manufacturer Orthodyne Electronics.  One project was a sinusoidal drive card to smooth out the bumps.  I understand that sine drives are available on the open market now.  We were rolling our own back then to save money because these wasn't enough competition to drive the price down.  Maybe a sine drive would help?   Jim Ford Sent from my Verizon, Samsung Galaxy smartphone


Timothy W. Koeth
 

Bruce & all,

Bruce, that is a great question. X-rays will probably be insufficient for
seeing defects in plastics and resins and low-Z (low atomic number)
materials, such as resins and epoxies, etc. The contrast in an x-ray comes
from the metals and high-Z materials stopping x-rays.

However, you've triggered the idea of neutron imaging! This is sort of the
complement to x-rays, neutrons can see through metals, but are stopped by a
plant leaf. Neutrons are absorbed by hydrogen and low-z bearing materials,
such as resins, wax, epoxy. Unlike every dentist's office having an x-ray
machine, neutron imaging machines require a neutron source, such as a
nuclear reactor, so they are generally not as accessible.

I have access to our Nuclear Reactor's neutron imaging system at the
University of Maryland. If someone is willing to send me a known dead HV
transformer, we can take neutron images of it to see if we can locate a
specific defect...

To get a sample idea of the images you can get with neutron imaging, please
have a look at: http://radiation.umd.edu/neutron-imaging/

Please let me know if this is something folks would try to do. Disclaimer,
this would be something new to try, and you might not get your transformer
back if there is some long-lived activation of the transformer, most often
this does not happen, but has happened once to me.

I am pursuing this type of imaging for looking for defects in additive
manufacturing. This could be a super cool application of it.

- Tim



Dr. Timothy Koeth
Assistant Professor
Material Science & Engineering
Institute for Research in Electronics and Applied Physics
University of Maryland
301-405-4952 (office)
609-577-8790 (cell)

https://mse.umd.edu/clark/faculty/676/Timothy-W-Koeth

radiation.umd.edu

Amateur radio call sign K0ETH "K-zero-ETH" (formerly N2LPN)


On Mon, Jan 25, 2021 at 3:57 PM greenboxmaven via groups.io <ka2ivy=
verizon.net@groups.io> wrote:

Has anyone ever tried grinding and carving the epoxy encapsulation down
to a very thin layer on the winding to see if the leakage would be
reduced? The work would require skill and patience to avoid damaging the
winding, getting it X-rayed before staring would help. Is the epoxy
transparent enough that the winding could be seen once you were close to
it without going too far? I have wondered if the conductivety goes all
the way through the epoxy, or if it is just below the surface.

Bruce Gentry, KA2IVY

On 1/25/21 15:12, Joel B Walker wrote:
I have a very nice 549 that I have owned for nearly 35 years. It worked
flawlessly at first, but then began showing the infamous epoxy HV
transformer potting issue. Back when it started doing this ('87-'88) I had
never heard of the epoxy problem before. I replaced the 6GE5, tested and
subbed caps and diodes in the circuit to no avail. Of course the screen
voltage on the 6GE5 was rising way over spec. so I knew it was being
overworked. Spraying the Transformer with freeze mist would bring
everything back to normal temporarily so finally decided the transformer
must be bad.
In the last few years I have been reading about everyone's troubles with
this same problem on many Tek scopes. I know Chuck Harris had been winding
these in the past but has stopped. So the dreaded question is; Is he going
to start back or is someone else going to start, is there a new solution,
or are we all SOL?











Chuck Harris
 

Hi Michael,

I am using an Arduino Mega256 driving a RAMPS style
shield. The motor drivers are the purple sort that
use HR8826 drivers, which max out at 32 usteps.

They sound smooth as silk, and visually they are
very smooth... However, there is more to it than the
eye can see. Every micro-step, the motor comes to
a stop before the next step. That causes the wire
tension to jerk, creasing the wire where it passes
through a saphire (ruby) jewel used as the stylus.

The problem with going to a higher micro-step value
is the frequency of the pulses needed to drive the
motor increase exponentially. The software used to
translate the G-codes to motor motion (GRBL) flat out
blows up if the step rate goes any higher than I am
currently doing. It isn't a pretty sight!

-Chuck Harris

Michael W. Lynch via groups.io wrote:

On Mon, Jan 25, 2021 at 03:49 PM, Chuck Harris wrote:


I use a micro-stepped stepper motor to directly drive the
former upon which the transformer is wound. The problem
is that even though it is micro-stepped 32x,
Chuck,

What stepper driver are you using? I found in my 3D printing, that using some of the more modern stepper drivers that are now available can help smooth and quiet the stepper motors. Perhaps the TMC22080 or another TRINAMIC driver could help eliminate this problem? Most of the newer drivers offer 256 native micro stepping as well as other advantages.


Harvey White
 

you might want to consider a 32 bit processor board combined with a TMC style driver.  IIRC the arduino interface can handle that.

Otherwise I have an old FPGA project that functions something like a smooth stepper, it does acelleration in hardware for all the axis driver.  It's not set for microstepping, though.

Harvey

On 1/25/2021 6:09 PM, Chuck Harris wrote:
Hi Michael,

I am using an Arduino Mega256 driving a RAMPS style
shield. The motor drivers are the purple sort that
use HR8826 drivers, which max out at 32 usteps.

They sound smooth as silk, and visually they are
very smooth... However, there is more to it than the
eye can see. Every micro-step, the motor comes to
a stop before the next step. That causes the wire
tension to jerk, creasing the wire where it passes
through a saphire (ruby) jewel used as the stylus.

The problem with going to a higher micro-step value
is the frequency of the pulses needed to drive the
motor increase exponentially. The software used to
translate the G-codes to motor motion (GRBL) flat out
blows up if the step rate goes any higher than I am
currently doing. It isn't a pretty sight!

-Chuck Harris

Michael W. Lynch via groups.io wrote:
On Mon, Jan 25, 2021 at 03:49 PM, Chuck Harris wrote:

I use a micro-stepped stepper motor to directly drive the
former upon which the transformer is wound. The problem
is that even though it is micro-stepped 32x,
Chuck,

What stepper driver are you using? I found in my 3D printing, that using some of the more modern stepper drivers that are now available can help smooth and quiet the stepper motors. Perhaps the TMC22080 or another TRINAMIC driver could help eliminate this problem? Most of the newer drivers offer 256 native micro stepping as well as other advantages.



Mlynch001
 

I am using a 32bit board and 4 TMC2208 drivers in one of my 3D printers. There is a noticeable difference in the operation of a printer with this combination. Smoother and motor torque (current) can be limited as well. I am constantly hoping that you will get this perfected. Life is getting in the way of a lot of things these days.

--
Michael Lynch
Dardanelle, AR


Jim Ford
 

Ok.   You know way more about it than I do.  Mechanical damping is most likely way simpler.   Good luck!     JimSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chuck Harris <cfharris@erols.com> Date: 1/25/21 2:52 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 549 transformer question There has to be a variable ratiometric connection between the motorthat drives the transformer's former, and the motor that drivesthe stylus in a back and forth motion.The machine I made sees the transformer's winding as beinga picture drawn on a long spool of paper wrapped around the coilformer.I create the winding by calculating the rotation angle, andthe stylus position based on the wire diameter, and the currentcircumference of the coil.  I feed the winder machine G-codes.I think steppers are the way to go, but I am looking intousing a damper on the drive for the coil former.  Tektronix did thison their 4663 flatbed plotter, to cure the same problem.-Chuck HarrisJim Ford wrote:> Say, Chuck, I worked with steppers and DC brushless motors briefly in the early 2000's at wirebonder manufacturer Orthodyne Electronics.  One project was a sinusoidal drive card to smooth out the bumps.  I understand that sine drives are available on the open market now.  We were rolling our own back then to save money because these wasn't enough competition to drive the price down.  Maybe a sine drive would help?   Jim Ford Sent from my Verizon, Samsung Galaxy smartphone


Harvey White
 

From looking at the drivers (hardware) and software support in the controller (and I'm repurposing a 3D printer board for something quite else), there's a fairly significant difference in how the system works based on the actual hardware drivers, and if the 3D printer software can support it.

Harvcey

On 1/25/2021 6:42 PM, Mlynch001 wrote:
I am using a 32bit board and 4 TMC2208 drivers in one of my 3D printers. There is a noticeable difference in the operation of a printer with this combination. Smoother and motor torque (current) can be limited as well. I am constantly hoping that you will get this perfected. Life is getting in the way of a lot of things these days.


shalopt
 

If some one removed the encapsulate and appeared to fix the problem.
Sounds like moisture so has anyone tried baking a transformer, or better
yet place in a vacuum chamber for 24-48 hours then bake at 150 degrees C.
Will not harm the wire or core but might get yet of the leakage.
Years ago I had Baltimore Transformer make some HV transformers for a
project their rig was driven by a gear motor. There problem was the potting
had to stand mil temperatures and 50K feet. Amazing the water collects in a
supposed sealed container going from flight level 1 to flight level 50 and return.
gary


Chuck Harris
 

Both have been done. The epoxy changes chemically. It has been
hypothesized that the change is due to a fire-retardant compound
added to the epoxy to keep the suits happy. It changed. No amount
of vacuum or drying will cause the epoxy to become what it once was
again.

Winding is the answer. I proved that almost 10 years ago. Another
guy Bill Schell proved it several years before me... And tektronix
knew it almost immediately after the first transformers started
failing in the 547 scopes.

-Chuck Harris

shalopt via groups.io wrote:

If some one removed the encapsulate and appeared to fix the problem.
Sounds like moisture so has anyone tried baking a transformer, or better
yet place in a vacuum chamber for 24-48 hours then bake at 150 degrees C.
Will not harm the wire or core but might get yet of the leakage.
Years ago I had Baltimore Transformer make some HV transformers for a
project their rig was driven by a gear motor. There problem was the potting
had to stand mil temperatures and 50K feet. Amazing the water collects in a
supposed sealed container going from flight level 1 to flight level 50 and return.
gary