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?

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?

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

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.

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

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

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.

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.

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.

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