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Transformer issue

K

krw

Jan 1, 1970
0
We're having problems with defective (or damaged in reflow) audio
transformers and I'm not buying what the manufacturer is telling us. A
significant number are falling out during manufacturing with what we
originally thought was a low DCR (12-15ohms vs 19ohms nominal) but the
turns ratio doesn't look altered significantly as measured with a 1kHz
tone. I've also found that the inductance drops through the floor
(600uH, perhaps vs. 1.8H, as indicated by an LR time constant
measurement).

The vendor is telling us that the RoHS reflow process is melting the
winding insulation but I'm not sure I'm buying it. Shorting a few
turns (even a third) doesn't seem like it should change the inductance
by over three orders of magnitude and it should also show up as a
significant change in the turns ratio, no? Also, I usually see a DCR
change but in a failing transformer both the primary and secondary
*always* have low inductance. The LR decay of our measurement isn't a
normal exponential, either. My guess is that something (heat) is
damaging the core somehow (turns ratio OK, L missing three zeros,
unnatural LR decay - no explanation for low DCR, though). The vendor
has agreed to fix the problem but their fix is high temperature wire,
which seems like a waste of time, though I'm certainly no transformer
expert. Any thoughts?
 
A

Andrew Holme

Jan 1, 1970
0
krw said:
We're having problems with defective (or damaged in reflow) audio
transformers and I'm not buying what the manufacturer is telling us. A
significant number are falling out during manufacturing with what we
originally thought was a low DCR (12-15ohms vs 19ohms nominal) but the
turns ratio doesn't look altered significantly as measured with a 1kHz
tone. I've also found that the inductance drops through the floor
(600uH, perhaps vs. 1.8H, as indicated by an LR time constant
measurement).

The vendor is telling us that the RoHS reflow process is melting the
winding insulation but I'm not sure I'm buying it. Shorting a few
turns (even a third) doesn't seem like it should change the inductance
by over three orders of magnitude and it should also show up as a
significant change in the turns ratio, no? Also, I usually see a DCR
change but in a failing transformer both the primary and secondary
*always* have low inductance. The LR decay of our measurement isn't a
normal exponential, either. My guess is that something (heat) is
damaging the core somehow (turns ratio OK, L missing three zeros,
unnatural LR decay - no explanation for low DCR, though). The vendor
has agreed to fix the problem but their fix is high temperature wire,
which seems like a waste of time, though I'm certainly no transformer
expert. Any thoughts?

Say you have 2 windings A and B with a turns ratio of 1000 : 1000 and the
first turn on A is shorted to the second. It's like having 3 windings A, B,
C with 999 : 1000 : 1. There isn't much difference in the A:B ratio, but
you have a short circuit across winding C. The 1000:1 turns ratio from A to
C makes for a 1000000 to 1 impedance ratio so it won't shunt the output of a
signal generator.

If you take a good transformer, measure the primary inductance, then short
the secondary and measure the primary inductance again, you get a much lower
inductance measurement when the secondary is shorted.
 
P

Phil Allison

Jan 1, 1970
0
"krakpot ratbag wanker"
We're having problems with defective (or damaged in reflow) audio
transformers and I'm not buying what the manufacturer is telling us.

** This NOTORIOUS trolling moron never " buys " the truth from anyone.

A
significant number are falling out during manufacturing with what we
originally thought was a low DCR (12-15ohms vs 19ohms nominal)

** So the DCR drops by 30% after reflow soldering and this ass thinks it is
NOT due to shorted turns ?

Maybe the copper wire has suddenly gone superconducting ??

ROTFL !!

Also, I usually see a DCR
change but in a failing transformer both the primary and secondary
*always* have low inductance.

** No fooling??

How amazing for it to affect both sides ....

ROTFL !!

My guess is that something (heat) is damaging the core somehow


** And making the DCR drop.

Only in some alternative universe inhabited entirely by FUCKWITS like
Keith.


...... Phil
 
J

Joerg

Jan 1, 1970
0
krw said:
We're having problems with defective (or damaged in reflow) audio
transformers and I'm not buying what the manufacturer is telling us. A
significant number are falling out during manufacturing with what we
originally thought was a low DCR (12-15ohms vs 19ohms nominal) but the
turns ratio doesn't look altered significantly as measured with a 1kHz
tone. I've also found that the inductance drops through the floor
(600uH, perhaps vs. 1.8H, as indicated by an LR time constant
measurement).

The vendor is telling us that the RoHS reflow process is melting the
winding insulation but I'm not sure I'm buying it. Shorting a few
turns (even a third) doesn't seem like it should change the inductance
by over three orders of magnitude and it should also show up as a
significant change in the turns ratio, no? Also, I usually see a DCR
change but in a failing transformer both the primary and secondary
*always* have low inductance. The LR decay of our measurement isn't a
normal exponential, either. My guess is that something (heat) is
damaging the core somehow (turns ratio OK, L missing three zeros,
unnatural LR decay - no explanation for low DCR, though). The vendor
has agreed to fix the problem but their fix is high temperature wire,
which seems like a waste of time, though I'm certainly no transformer
expert. Any thoughts?

I think your vendor is right in changing to high-temp wire. A single
shorted turn renders a transformer useless, inductance collapses as Tim
said. Once shorted a turns ratio measurement via an audio test may not
be all that meaningful anymore. It's like testing the cornering
performance of a car with the parking brake pulled :)

Usually in cases like this the mfg would want some failed transformers
back and do a failure analysis on those. Peel them apart. With photos
and so on, photos that should be shared with you.
 
K

krw

Jan 1, 1970
0
Say you have 2 windings A and B with a turns ratio of 1000 : 1000 and the
first turn on A is shorted to the second. It's like having 3 windings A, B,
C with 999 : 1000 : 1. There isn't much difference in the A:B ratio, but
you have a short circuit across winding C.
^^^^^^^^^
*THAT* is what I was missing. Thanks! It all makes sense now.
The 1000:1 turns ratio from A to
C makes for a 1000000 to 1 impedance ratio so it won't shunt the output of a
signal generator.

If you take a good transformer, measure the primary inductance, then short
the secondary and measure the primary inductance again, you get a much lower
inductance measurement when the secondary is shorted.

I would expect that, but didn't consider the shorted winding to be a
separate winding. I imagined it as simply shorted (out of the
circuit). Thank you very much for the explanation.
 
K

krw

Jan 1, 1970
0
"krakpot ratbag wanker"

Ah, Another of Nymbecile's Nyms.
** This NOTORIOUS trolling moron never " buys " the truth from anyone.



** So the DCR drops by 30% after reflow soldering and this ass thinks it is
NOT due to shorted turns ?

Maybe the copper wire has suddenly gone superconducting ??

ROTFL !!



** No fooling??

How amazing for it to affect both sides ....

ROTFL !!




** And making the DCR drop.

Only in some alternative universe inhabited entirely by FUCKWITS like
Keith.

You read as well as Nybecile, too, Phyllis.
 
K

krw

Jan 1, 1970
0
I think your vendor is right in changing to high-temp wire. A single
shorted turn renders a transformer useless, inductance collapses as Tim
said. Once shorted a turns ratio measurement via an audio test may not
be all that meaningful anymore. It's like testing the cornering
performance of a car with the parking brake pulled :)

Usually in cases like this the mfg would want some failed transformers
back and do a failure analysis on those. Peel them apart. With photos
and so on, photos that should be shared with you.

Oh, they have a pile back already. They haven't shared any photos,
though. I just wanted to be comfortable that their fix is actually
going to do something.

This is becoming a rather painful issue. The fallout has gone from 1%
to maybe 10%. With 15 transformers per board it's a royal PITA for
manufacturing. Hopefully we'll get an ICT screen in place in a week
or so but changing that many transformers is still a big kink in the
line.
 
P

Phil Allison

Jan 1, 1970
0
"krakpot ratbag wanker"
We're having problems with defective (or damaged in reflow) audio
transformers and I'm not buying what the manufacturer is telling us.

** This NOTORIOUS trolling moron never " buys " the truth from anyone.

A
significant number are falling out during manufacturing with what we
originally thought was a low DCR (12-15ohms vs 19ohms nominal)

** So the DCR drops by 30% after reflow soldering and this ass thinks it is
NOT due to shorted turns ?

Maybe the copper wire has suddenly gone superconducting ??

ROTFL !!

Also, I usually see a DCR
change but in a failing transformer both the primary and secondary
*always* have low inductance.

** No fooling??

How amazing for it to affect both sides ....

ROTFL !!

My guess is that something (heat) is damaging the core somehow


** And making the DCR drop.

Only in some alternative universe inhabited entirely by FUCKWITS like
Keith.


...... Phil
 
J

Joerg

Jan 1, 1970
0
krw said:
Oh, they have a pile back already. They haven't shared any photos,
though. I just wanted to be comfortable that their fix is actually
going to do something.

I think it will.

This is becoming a rather painful issue. The fallout has gone from 1%
to maybe 10%. With 15 transformers per board it's a royal PITA for
manufacturing. Hopefully we'll get an ICT screen in place in a week
or so but changing that many transformers is still a big kink in the
line.

I'd solder them on by hand until further notice, until they deliver them
with high-temp wire.
 
K

krw

Jan 1, 1970
0
I think it will.



I'd solder them on by hand until further notice, until they deliver them
with high-temp wire.

That's a good suggestion. I don't know if they're going to like that
answer either.
 
P

Phil Allison

Jan 1, 1970
0
"Dave Platt"
I wonder if you haven't developed a DC leakage path which completely
bypasses the windings? In effect, an R in parallel with one of the
windings.


** That " leakage " R would need to be around 50 ohms and quite linear.

Maybe you think the moon IS made from green cheese too.

Ever heard of "Occams Razor" ??

Obviously not.


..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"krakpot ratbag wanker"
We're having problems with defective (or damaged in reflow) audio
transformers and I'm not buying what the manufacturer is telling us.

** This NOTORIOUS trolling moron never " buys " the truth from anyone.

A significant number are falling out during manufacturing with what we
originally thought was a low DCR (12-15ohms vs 19ohms nominal)

** So the DCR drops by 30% after reflow soldering and this ass thinks it is
NOT due to shorted turns ?

Maybe the copper wire has suddenly gone superconducting ??

ROTFLMAO !!

Also, I usually see a DCR
change but in a failing transformer both the primary and secondary
*always* have low inductance.

** No fooling ?????

How amazing for it to affect both sides ....

You FUCKING MORON !!!

ROTFL !!

My guess is that something (heat) is damaging the core somehow...


** And making the DCR drop ??????????

Only in some alternative universe inhabited entirely by UTTER FUCKWITS
like Keith Ratbag.

PISS OFF TO HELL YOU DAMN TROLL



...... Phil
 
J

Joerg

Jan 1, 1970
0
krw said:
krw wrote:
[...]
I'd solder them on by hand until further notice, until they deliver them
with high-temp wire.

That's a good suggestion. I don't know if they're going to like that
answer either.


The production folks? Invite them for lunch and explain the situation,
works really well IME. If they are kept in the loop and feel like part
of the family they'd do almost anything for you :)
 
K

krw

Jan 1, 1970
0
krw said:
krw wrote:
[...]
This is becoming a rather painful issue. The fallout has gone from 1%
to maybe 10%. With 15 transformers per board it's a royal PITA for
manufacturing. Hopefully we'll get an ICT screen in place in a week
or so but changing that many transformers is still a big kink in the
line.

I'd solder them on by hand until further notice, until they deliver them
with high-temp wire.

That's a good suggestion. I don't know if they're going to like that
answer either.


The production folks? Invite them for lunch and explain the situation,
works really well IME. If they are kept in the loop and feel like part
of the family they'd do almost anything for you :)

I don't know which is worse, replacing 10% (perhaps a high number) or
hand placing 100%. I'll certainly suggest it tomorrow, though (I'm
out next week ;).
 
K

krw

Jan 1, 1970
0
The consensus here is that their fix will work. Sometimes better the
devil you know...
 
K

krw

Jan 1, 1970
0
But doesn't it take some time to discover which 10% are bad even before you
desolder and replace them?

I'm 99% sure a simple ICT screen will catch them. They've been
relying on DCR but that clearly isn't going to work. A simple RL
timing circuit will, though.
We were just discussing yesterday whether op-amps or transformers would make
for a better hybrid (interfacing to the old two-wire "party line" intercom
systems)... maybe op-amps deserve another look!

A lot depends on how well controlled your environment is. I found
that op-amps work better in our application (we needed better than
30dB isolation for ECAN to work properly). The transformers are for
coupling and interface standardization to the outside world. We use
two transformers in the hybrid on each 2-wire channel, one for the
line and the other in the matching network (sort of a bridge
topology).
 
S

StickThatInYourPipeAndSmokeIt

Jan 1, 1970
0
You stop in every couple or few weeks, and do nothing at all except
spew horseshit into the groups. That is all you do any more. Not that
you ever did much else.
 
P

Phil Allison

Jan 1, 1970
0
"krakpot ratbag wanker"
We're having problems with defective (or damaged in reflow) audio
transformers and I'm not buying what the manufacturer is telling us.

** This NOTORIOUS trolling moron never " buys " the truth from anyone.


A significant number are falling out during manufacturing with what we
originally thought was a low DCR (12-15ohms vs 19ohms nominal)

** So the DCR drops by 30% after reflow soldering and this ass thinks it is
NOT due to shorted turns ?

Maybe the copper wire has suddenly gone superconducting ??

ROTFLMAO !!


Also, I usually see a DCR
change but in a failing transformer both the primary and secondary
*always* have low inductance.

** No fooling ?????

How amazing for it to affect both sides ....

You FUCKING MORON !!!

ROTFL !!

My guess is that something (heat) is damaging the core somehow...


** And making the DCR drop ??????????

Only in some alternative universe inhabited entirely by

UTTER FUCKWITS like Keith Ratbag.

PISS OFF TO HELL YOU DAMN TROLL



...... Phil
 
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