Topics

Slightly OT: How can I dissolve Potting Compound?


 

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by
Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF


Vince Vielhaber
 

A heat gun is often the method for removing the potting, but care must be taken since some of the potting compounds get very toxic with heat.

Is there a model number on the dead supply?

Vince.

On 01/02/2021 09:18 PM, Dennis Tillman W7pF wrote:
I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by
Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF




Glenn Little
 

You can try MEK, methyl ethyl keytone.
It will dissolve a lot of epoxies.
Be careful to not dissolve other things.

73
Glenn
WB4UIV

On 1/2/2021 9:18 PM, Dennis Tillman W7pF wrote:
I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by
Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF



--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"


EJP
 

On Sun, Jan 3, 2021 at 01:24 PM, Vince Vielhaber wrote:

A heat gun is often the method for removing the potting, but care must
be taken since some of the potting compounds get very toxic with heat.
It is also extremely smelly. Work outdoors or with fume exraction, or at least seriously good ventilation.

EJP


Ed Breya
 

Breaking down epoxies at room temperature has often come up here and in the hpagilent group. My standard answer is Dimethylformamide, but other solvents can do it too. It's a messy process and some internal parts may get damaged or lose their identity. I think it would be cheaper and cleaner to just get a fresh HeNe driver in the same size class as the original (probably for standard 1 mW HeNe). These used to be commodity items, and I would think used or NOS ones ought to be available cheap since HeNe lasers aren't used so much anymore.

As I recall, the ones I have are labeled something around 2-2.5 kV at 6-15 ma running, depending on tube size, with ignition voltage up to around 10-12 kV. I can't recall the ballast resistor size, but think around 75 kohms, 5W is typical. If your other driver is too big for the discharge tubes you have, you can up the ballast resistance. Also, the driver boxes usually have auto-ignition, so if it doesn't see approximately the normal HeNe load, it will re-strike maybe up to ten times a second, thinking the tube isn't lit. This could be the apparent stability problem you see. All these things can be fixed externally, but it's simplest to get the small kind that you had working already.

Ed


stevenhorii
 

If the heat gun can melt epoxy resins, it may be hot enough to melt other
plastics - like the insulation on wires (unless it's Teflon or silicone -
which it may be in an HV supply).
There are quite a few spectral lamp power supplies on eBay (some show up
under "arc lamp power supply", but most I would call questionable. One
shown operating with a lamp is the most expensive. Likely not worth taking
a chance on the others but you could take a look.

Steve H.

On Sat, Jan 2, 2021 at 10:08 PM EJP <esmond.pitt@bigpond.com> wrote:

On Sun, Jan 3, 2021 at 01:24 PM, Vince Vielhaber wrote:

A heat gun is often the method for removing the potting, but care must
be taken since some of the potting compounds get very toxic with heat.
It is also extremely smelly. Work outdoors or with fume exraction, or at
least seriously good ventilation.

EJP






Jim Ford
 

MEK is really nasty stuff and a precursor to methamphetamine, from what I understand.  A funny but horrifying story about MEK came from a coworker.  Seems a coworker of his years ago wanted some of the used MEK to clean engine parts.  His boss signed off on a 55 gallon drum of the stuff, which he put in the back of his pickup truck.  On down the road, it started leaking onto the highway, which caught the attention of a state trooper!  Not only was he dripping MEK, but he had crossed the state line and had some serious explaining to do!  He and his boss got fired in short order.   Moral of the story is be very careful if you're going to use MEK.  IIRC, MEK is flammable and carcinogenic.     Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Glenn Little <glennmaillist@bellsouth.net> Date: 1/2/21 6:26 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound? You can try MEK, methyl ethyl keytone.It will dissolve a lot of epoxies.Be careful to not dissolve other things.73GlennWB4UIVOn 1/2/2021 9:18 PM, Dennis Tillman W7pF wrote:> I need to dissolve the black HV potting compound of a 12VDC powered> Helium-Neon laser inverter power supply I have that stopped working. I would> appreciate any suggestions on what works to do this. I’m guessing it may be> epoxy. I stuck the tip of a hot soldering iron in it for a few seconds> without much effect.>> When it was working it turned out to be perfect for powering gas filled> Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled> with a variety of gasses are an excellent source of spectral lines for the> 7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.>> Spectrum tubes require an initial high voltage (1,000V to 1,500V for> example) to break down the gas and start it conducting. Once the gas in the> spectrum tube conducts the voltage across the gas drops (250V to 450V for> example) and unless you limit the current (to a few mA) it will destroy the> tube. Can anyone can point me to a source of information on how to determine> the proper voltage and current I need to power these spectrum tubes? Is> there a web site or group devoted to Spectrum Tubes?>> Something happened to the inverter and it stopped working. The input is now> open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast> resistor has continuity so that is not the problem. The original label on> the inverter is partially destroyed so I can’t tell what its initial high> voltage output was or what it current limits at. All I do know is that it> was made by> Laser Drive Inc.> 5465 Wm. Flynn Hwy. Gibsonia, PA 15044> Model: 1150-6330, S/N: 610574> The input was +12VDC at 0.35A.>> I wrote to the company that took over the company that took over Laser Drive> Inc. asking if they could tell me the output voltage and limiting current> but I didn’t receive a reply.>> At this point I am hoping if I can remove the potting compound I can figure> out what went wrong with it.>> I have a different, bigger Laser Drive Inc. potted inverter which is powered> by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to> flicker. They do not run continuously. I am guessing that this because 6.5mA> is more current than the tube can conduct. The amount of current the tube> draws increases in proportion to the inside diameter of the tube but I don’t> know much about this matching the power supply to the tube. All I do know is> the one that went bad seems to be an ideal match for the spectrum tubes I> have.>> Battery operated (DC input) inverters are much more desirable than AC input> inverters for this application because the AC rectification and poor> filtering shows up on the output DC as significant ripple causing the> amplitude of each spectral line to be blurred.>> Dennis Tillman W7pF>>> >>-- -----------------------------------------------------------------------Glenn Little                ARRL Technical Specialist   QCWA  LM 28417Amateur Callsign:  WB4UIV            wb4uiv@arrl.net    AMSAT LM 2178QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA-LM    ARRL TAPR"It is not the class of license that the Amateur holds but the classof the Amateur that holds the license"


Roy Thistle
 

Hi Dennis:
If it is some kind of epoxy, then acetone dissolves it better then MEK.
Cured epoxy resins, like moulded parts, can be exposed to MEK... and show "fair" resistance. (MEK will eventually damage the part.) Exposure to acetone is "not recommended."
Using either one... you'll have to immerse... and leave it in soak.
As for the results... mileage will vary, according to what's inside (other resin parts/plastic parts might get attacked/dissolved too) ; so, there may be damage.
Usually, what is left is enough of an indication to understand what was there; but, the damage may be so that repairing it is not possible. (If there is a pcb inside, you can usually trace that out.)
Careful with acetone. It has a low flash point... but, is less toxic than MEK.


Leon Robinson
 

My first experience with MEK was in early 1966 in the Navy,I spilled some on my belly, It burned like fire, buy the time
I got my pants down to wash it off it was gone, just a patch of
very white skin that was very tender.I never messed with MEK again.
I wonder if that had anything to do  with my having Kidney
cancer in my right kidney in 2010.
To stay on topic many Laser power supplies were potted with a
soft and flow able epoxy that was vacuum impregnated and sealed
with a hard black epoxy, I used to work for one of Lased Drive's competitors.Try grinding off one corner of the case and pry it up and see
what is inside.

Leon Robinson    K5JLR

Political Correctness is a Political Disease.

Politicians and Diapers should be changed
often and for the same reasons.

On Saturday, January 2, 2021, 10:38:48 PM CST, Jim Ford <james.ford@cox.net> wrote:

MEK is really nasty stuff and a precursor to methamphetamine, from what I understand.  A funny but horrifying story about MEK came from a coworker.  Seems a coworker of his years ago wanted some of the used MEK to clean engine parts.  His boss signed off on a 55 gallon drum of the stuff, which he put in the back of his pickup truck.  On down the road, it started leaking onto the highway, which caught the attention of a state trooper!  Not only was he dripping MEK, but he had crossed the state line and had some serious explaining to do!  He and his boss got fired in short order.   Moral of the story is be very careful if you're going to use MEK.  IIRC, MEK is flammable and carcinogenic.     Jim Ford Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Glenn Little <glennmaillist@bellsouth.net> Date: 1/2/21  6:26 PM  (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound? You can try MEK, methyl ethyl keytone.It will dissolve a lot of epoxies.Be careful to not dissolve other things.73GlennWB4UIVOn 1/2/2021 9:18 PM, Dennis Tillman W7pF wrote:> I need to dissolve the black HV potting compound of a 12VDC powered> Helium-Neon laser inverter power supply I have that stopped working. I would> appreciate any suggestions on what works to do this. I’m guessing it may be> epoxy. I stuck the tip of a hot soldering iron in it for a few seconds> without much effect.>> When it was working it turned out to be perfect for powering gas filled> Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled> with a variety of gasses are an excellent source of spectral lines for the> 7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.>> Spectrum tubes require an initial high voltage (1,000V to 1,500V for> example) to break down the gas and start it conducting. Once the gas in the> spectrum tube conducts the voltage across the gas drops (250V to 450V for> example) and unless you limit the current (to a few mA) it will destroy the> tube. Can anyone can point me to a source of information on how to determine> the proper voltage and current I need to power these spectrum tubes? Is> there a web site or group devoted to Spectrum Tubes?>> Something happened to the inverter and it stopped working. The input is now> open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast> resistor has continuity so that is not the problem. The original label on> the inverter is partially destroyed so I can’t tell what its initial high> voltage output was or what it current limits at. All I do know is that it> was made by> Laser Drive Inc.> 5465 Wm. Flynn Hwy. Gibsonia, PA 15044> Model: 1150-6330, S/N: 610574> The input was +12VDC at 0.35A.>> I wrote to the company that took over the company that took over Laser Drive> Inc. asking if they could tell me the output voltage and limiting current> but I didn’t receive a reply.>> At this point I am hoping if I can remove the potting compound I can figure> out what went wrong with it.>> I have a different, bigger Laser Drive Inc. potted inverter which is powered> by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to> flicker. They do not run continuously. I am guessing that this because 6.5mA> is more current than the tube can conduct. The amount of current the tube> draws increases in proportion to the inside diameter of the tube but I don’t> know much about this matching the power supply to the tube. All I do know is> the one that went bad seems to be an ideal match for the spectrum tubes I> have.>> Battery operated (DC input) inverters are much more desirable than AC input> inverters for this application because the AC rectification and poor> filtering shows up on the output DC as significant ripple causing the> amplitude of each spectral line to be blurred.>> Dennis Tillman W7pF>>> >>-- -----------------------------------------------------------------------Glenn Little                ARRL Technical Specialist   QCWA  LM 28417Amateur Callsign:  WB4UIV            wb4uiv@arrl.net    AMSAT LM 2178QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA-LM    ARRL TAPR"It is not the class of license that the Amateur holds but the classof the Amateur that holds the license"


Roy Thistle
 

On Sat, Jan 2, 2021 at 08:38 PM, Jim Ford wrote:


MEK is really nasty stuff and a precursor to
Gasoline is worse, but...
MEK is listed as a precursor... but a lot of industrial chemicals are precursors... and despite being listed... it produced, and used in vast quantities, in the U.S.
Model airplane "glue" (actually solvent welding, not gluing) has it, plumbing "glue" has it (dido of welding plastic pipe)... it's used in a lot of products sold to the public.
If plumbers and kids can handle it... well...
It's not "particularly good" at dissolving the black epoxy potting compound, after it's cured... but, depends which epoxy was used... and given a long time... it might dissolve it.
Acetone works better. (But, don't tell your wife of the horrors... or she might have nightmares after she does her nails.)


Dave Seiter
 

I've found that nail polish remover can have weird stuff in it (besides the obvious dyes and fragrances) that pure acetone doesn't.  Last summer I poured half a bottle into the plastic tub of a cheapo ultrasonic cleaner, and it immediately started attacking the plastic.  The thing is-  I've used pure acetone in that tub many many times and it's never touched it.  
-Dave

On Saturday, January 2, 2021, 09:09:47 PM PST, Roy Thistle <roy.thistle@mail.utoronto.ca> wrote:

On Sat, Jan  2, 2021 at 08:38 PM, Jim Ford wrote:


MEK is really nasty stuff and a precursor to
Gasoline is worse, but...
MEK is listed as a precursor... but a lot of industrial chemicals are precursors... and despite being listed... it produced, and used in vast quantities, in the U.S.
Model airplane "glue" (actually solvent welding, not gluing) has it, plumbing "glue" has it (dido of welding plastic pipe)... it's used in a lot of products sold to the public.
If plumbers and kids can handle it... well...
It's not "particularly good" at dissolving the black epoxy potting compound, after it's cured... but, depends which epoxy was used... and given a long time... it might dissolve it.
Acetone works better. (But, don't tell your wife of the horrors... or she might have nightmares after she does her nails.)


Roy Thistle
 

On Sat, Jan 2, 2021 at 06:18 PM, Dennis Tillman W7pF wrote:


Helium-Neon laser inverter power supply
Hi Dennis:
I couldn't remember... but finally did.
There is the defacto go to FAQ... for "gas laser tube nuts" called "Sam's Laser FAQ" ... there is good bit of information about He-Ne laser power supplies, et. al. (No relation to the schematic service, for T.V. repair... and not a quack [ is/was a prof. and has a PhD, if that precludes that sort of thing.] )
Gas discharge laser tubes are similar to "spectrum discharge tubes" ... at least the spectrum tubes I'm familiar with.
There's several scientific supply houses, in the U.S. that sell those spectrum tubes (but, I think they are all made in China.) The tubes I'm thinking of are about a foot long, have cold cathode electrodes on either end, and are made of glass.


Roy Thistle
 

On Sat, Jan 2, 2021 at 10:31 PM, Dave Seiter wrote:


nail polish remover can have weird stuff in it
Yup.
Some nail polish removers use acetone.
Some removers use ethyl acetate or MEK or both.
Remember MEK is used in the "glue" that plumbers use to solvent weld together plastic pipe.... in other words... it softens (and would dissolve) the plastic.


Tom Bowers
 

Dennis,

A chemist friend once told me to try Dichloromethane. I have successfully
unpotted two assemblies using this.

First, it is nasty stuff, I put the part and the Dichloromethane in a glass
jar with a tight fitting lid and left it outside in the sun. The jar was
about half full and completely covered the part. If anything happened to
the jar, it would just spill into the driveway. I did this in a reasonably
warm part of the year. It would boil from the heat of the sun, condense at
night, and do the same the next day. A tight fitting lid contained the
liquid for months.

Second, it is slow. I unpotted a motorcycle voltage regulator and a 7904 HV
multiplier. In both cases, it took over a month.

Third, it will eat anything plastic. It doesn't know the difference between
potting compound and the plastic case of a diode or transistor.

Fourth, frequent investigation can get you info. On day 10, a transistor
may become partially visible, make note and move on. On day 15, a diode may
become visible, and the transistor from day 10 might be just the metal lead
frame and die. Looking every few days will yield new info. If you catch it
at just the right time, you can make electrical measurements of the
partially exposed leads.

For the 7904 HV multiplier, all the ceramic caps were stripped of
insulation but the leads and conductors were still there. The output
resistor was still measurable, as was the low voltage feedback diode, which
was the mystery for me at the time. I was even able to carefully measure a
diode and a capacitor before the leads fell apart.

It just depends on how desperate you are. As others have suggested,
purchasing a new one would be far easier. And there will be no chance of
repair, just the possibility of capturing a schematic and mechanical
details.

Tom Bowers
PVH Engineering

"
"
Dennis Tillman W7pF via
<https://support.google.com/mail/answer/1311182?hl=en> groups.io
7:18 PM (4 hours ago)
to TekScopes
I need to dissolve the black HV potting compound........ "

On Sat, Jan 2, 2021 at 11:31 PM Dave Seiter <d.seiter@att.net> wrote:

I've found that nail polish remover can have weird stuff in it (besides
the obvious dyes and fragrances) that pure acetone doesn't. Last summer I
poured half a bottle into the plastic tub of a cheapo ultrasonic cleaner,
and it immediately started attacking the plastic. The thing is- I've used
pure acetone in that tub many many times and it's never touched it.
-Dave
On Saturday, January 2, 2021, 09:09:47 PM PST, Roy Thistle <
roy.thistle@mail.utoronto.ca> wrote:

On Sat, Jan 2, 2021 at 08:38 PM, Jim Ford wrote:


MEK is really nasty stuff and a precursor to
Gasoline is worse, but...
MEK is listed as a precursor... but a lot of industrial chemicals are
precursors... and despite being listed... it produced, and used in vast
quantities, in the U.S.
Model airplane "glue" (actually solvent welding, not gluing) has it,
plumbing "glue" has it (dido of welding plastic pipe)... it's used in a lot
of products sold to the public.
If plumbers and kids can handle it... well...
It's not "particularly good" at dissolving the black epoxy potting
compound, after it's cured... but, depends which epoxy was used... and
given a long time... it might dissolve it.
Acetone works better. (But, don't tell your wife of the horrors... or she
might have nightmares after she does her nails.)










Richard Knoppow
 

Also xylene. Be careful of MEK, it will dissolve rubber gloves.

On 1/2/2021 11:02 PM, Roy Thistle wrote:
On Sat, Jan 2, 2021 at 10:31 PM, Dave Seiter wrote:

nail polish remover can have weird stuff in it
Yup.
Some nail polish removers use acetone.
Some removers use ethyl acetate or MEK or both.
Remember MEK is used in the "glue" that plumbers use to solvent weld together plastic pipe.... in other words... it softens (and would dissolve) the plastic.



--
Richard Knoppow
dickburk@ix.netcom.com
WB6KBL


Dave Seiter
 

I guess the point I was getting at but missed, was that it was labeled as containing acetone, but nothing else.  I try to stay away from beauty products (they wouldn't help me- hahaha!), but when it was being tossed out, I said "Acetone? I'll take it!".  Now I know better.
-Dave

On Saturday, January 2, 2021, 11:02:31 PM PST, Roy Thistle <roy.thistle@mail.utoronto.ca> wrote:

On Sat, Jan  2, 2021 at 10:31 PM, Dave Seiter wrote:


nail polish remover can have weird stuff in it
Yup.
Some nail polish removers use acetone.
Some removers use ethyl acetate or MEK or both.
Remember MEK is used in the "glue" that plumbers use to solvent weld together plastic pipe.... in other words... it softens (and would dissolve) the plastic.


Dave Daniel
 

My approach to this sort of problem (I’ve done it twice in the past thirty or so years) has been to use an Xacto knife to cut the potting compound away. I never did find a solvent that seemed to work.

DaveD

On Jan 2, 2021, at 21:18, Dennis Tillman W7pF <dennis@ridesoft.com> wrote:

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1½” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by
Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF





Dave Brown
 

Supposedly a 50/50 mix of formic and acetic acids will do the trick but I've never tried it.
DaveB, NZ

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dave Daniel
Sent: Sunday, January 03, 2021 21:59
To: TekScopes@groups.io
Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound?

My approach to this sort of problem (I’ve done it twice in the past thirty or so years) has been to use an Xacto knife to cut the potting compound away. I never did find a solvent that seemed to work.

DaveD

On Jan 2, 2021, at 21:18, Dennis Tillman W7pF <dennis@ridesoft.com> wrote:

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would appreciate any suggestions on what works to do this. I’m
guessing it may be epoxy. I stuck the tip of a hot soldering iron in
it for a few seconds without much effect.

When it was working it turned out to be perfect for powering gas
filled Spectrum Tubes. These spectrum tubes (smaller versions of neon
signs) filled with a variety of gasses are an excellent source of
spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas
in the spectrum tube conducts the voltage across the gas drops (250V
to 450V for
example) and unless you limit the current (to a few mA) it will
destroy the tube. Can anyone can point me to a source of information
on how to determine the proper voltage and current I need to power
these spectrum tubes? Is there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input
is now open. The inverter is a black potted brick 3” x 1½” x 1”. The
ballast resistor has continuity so that is not the problem. The
original label on the inverter is partially destroyed so I can’t tell
what its initial high voltage output was or what it current limits at.
All I do know is that it was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser
Drive Inc. asking if they could tell me the output voltage and
limiting current but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can
figure out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is
powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the
Spectrum Tubes to flicker. They do not run continuously. I am guessing
that this because 6.5mA is more current than the tube can conduct. The
amount of current the tube draws increases in proportion to the inside
diameter of the tube but I don’t know much about this matching the
power supply to the tube. All I do know is the one that went bad seems
to be an ideal match for the spectrum tubes I have.

Battery operated (DC input) inverters are much more desirable than AC
input inverters for this application because the AC rectification and
poor filtering shows up on the output DC as significant ripple causing
the amplitude of each spectral line to be blurred.

Dennis Tillman W7pF





Nenad Filipovic
 

Hi Dennis,

On Sat, Jan 2, 2021 at 06:18 PM, Dennis Tillman W7pF wrote:
I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working.
I believe it's not worth the effort, I'd personally build a new one using instructions from Sam's Laser FAQ:
https://www.repairfaq.org/sam/laserhps.htm#hpstoc
You'll find wealth of information on this site, it's amazing (even I contributed with my unusual Argon laser specimen).

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube.
I have no experience with spectral tubes but from your description it appears they work in the same way as a HeNe laser tubes do. Therefore a matching HeNe power supply will work for sure, but to my recollection the values you stated are much lower than the usual for HeNe tubes. These start with approx. 5-15kV and work (steadily conduct) at approx. 1-2kV. So to use an off the shelf HeNe PSU I'd try under-powering it (in therms of voltage) and/or increasing the ballast resistor.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.
The PSU needs to be matched to the particular tube you're using, my experience with HeNe tubes is the following:
- High voltage for initial start has ample tolerance, it just needs to be able to start the tube. It is universally implemented as a diode-capacitor ladder multiplier so you can add elements until you get it high enough. Capacitors are normally small as you don't need excessive energy to kick-start the tube (e.g. CRT HV power supply can deliver orders of magnitude more energy than HeNe HV starter).
- Ballast resistor and working voltage need to be fairly matched. The flicker you experienced with the other PSU is exactly the symptom of a mismatch. The ballast resistor cannot counter the intrinsic negative impedance of the working gas tube and the resulting runaway results in tube shutting down. The flicker is due to HV start occurring in a random loop. You can safely try to increase the ballast resistor and see if that improves the situation. This helps with aged HeNe tubes when they start flickering at end of life, sometimes ballast needs to be increased as much as threefold. The ballast resistor needs to be low enough to supply enough current through the tube to maintain plasma, but also high enough to limit the current.
- The working voltage of a traditional transformer based PSU can be adjusted using a variac. Since in your case you most likely need to go down with the voltage, I'd say variac approach will give you ample headroom to match the HeNe PSU to your tubes.

HTH
Best regards and Happy New Year,
Nenad Filipovic


Jean-Paul
 

Dear Dennis: We worked on arc and gas lamp ballasts since 1970s.
Then designed and manufactured 12 kV HV modules, in 1980s..1990s.
The encapsulant is a very high solids epoxy, specially cured.
We used heat and mechanical picking to disassemble.

The components can be damaged by the depotting process, so it is a destructive diagnostic but you will not revive the PSU.
Especially susceptible is the transformer insulation, it will be contaminated in the process.
Better idea is to replace with a new one.

Finally the laser supply and spectral lamps have very different performance, eg lasers DC with HV ignition pulse, spectral can use current limited AC similar to a neon sign transformer.

If you have a small neon transformer, try that on a variac.

If you PM me the specs and exact model of tubes, I may have an off the shelf supply I could send to you.

Happy New Years,

Jon