SMPS repair tip

[Phil Allison]

** Hi,

recently I wasted much time trying to get a small, off-line SMPS to work
properly. The supply was part of a 1000W class D audio amplifier and built
onto the same PCB smothered in mostly SMD parts.

The design employed an 8 pin DIL chip (Infineon ICE 2A165) that did almost
everything and it along with some SMD diodes and two 1W resistors had
failed.

After replacing all the damaged parts - it would operate briefly, then shut
down and seemed to be very fussy about the amount of load applied and DC
supply voltage too. All the waveforms look pretty good on my scope except
that across the 1 ohm current sense resistor - which showed a lot of
ringing at several MHz.

I even removed the ferrite transformer from the PCB to test it independently
and confirm it was OK.

Finally, I tried a 47nF cap directly across the 1 ohm resistor - which made
a big improvement to the behaviour. Smelling a fat rat, I removed the
resistor and broke it apart to find if it was really metal film - bingo !!

Although my resistor looked almost identical to the original, I had
accidentally swapped a film resistor for a wirewound type. It had about 12
turns of wire on the ceramic core instead of the 3 turn spiral a MF type
typically has so a tad more inductance.

Both resistors had near identical, smooth, light grey bodies with the same
coloured bands in exactly the same places - what a trap.

With a genuine MF type fitted, ringing was suppressed by about two thirds
and the SMPS finally worked as intended.



..... Phil

 

[dave]

On 07/26/2014 10:21 PM, Phil Allison wrote:

** Hi,

recently I wasted much time trying to get a small, off-line SMPS to work
properly. The supply was part of a 1000W class D audio amplifier and built
onto the same PCB smothered in mostly SMD parts.

The design employed an 8 pin DIL chip (Infineon ICE 2A165) that did almost
everything and it along with some SMD diodes and two 1W resistors had
failed.

After replacing all the damaged parts - it would operate briefly, then shut
down and seemed to be very fussy about the amount of load applied and DC
supply voltage too. All the waveforms look pretty good on my scope except
that across the 1 ohm current sense resistor - which showed a lot of
ringing at several MHz.

I even removed the ferrite transformer from the PCB to test it independently
and confirm it was OK.

Finally, I tried a 47nF cap directly across the 1 ohm resistor - which made
a big improvement to the behaviour. Smelling a fat rat, I removed the
resistor and broke it apart to find if it was really metal film - bingo !!

Although my resistor looked almost identical to the original, I had
accidentally swapped a film resistor for a wirewound type. It had about 12
turns of wire on the ceramic core instead of the 3 turn spiral a MF type
typically has so a tad more inductance.

Both resistors had near identical, smooth, light grey bodies with the same
coloured bands in exactly the same places - what a trap.

With a genuine MF type fitted, ringing was suppressed by about two thirds
and the SMPS finally worked as intended.



.... Phil

I worked at a pro audio company using wirewound power resistors to test
Class D power amps. I couldn't convince them to consider the reactance
effects at hypersonic frequencies, not only the switching artifacts but
the Power Factor Controllers too, create a rich VLF stew. It won't hurt
speakers but it may affect efficiency and heat load. Am I nuts?

 

[Cydrome Leader]

dave <ricketzz@earthlink.net> wrote:

On 07/26/2014 10:21 PM, Phil Allison wrote:
** Hi,

recently I wasted much time trying to get a small, off-line SMPS to work
properly. The supply was part of a 1000W class D audio amplifier and built
onto the same PCB smothered in mostly SMD parts.

The design employed an 8 pin DIL chip (Infineon ICE 2A165) that did almost
everything and it along with some SMD diodes and two 1W resistors had
failed.

After replacing all the damaged parts - it would operate briefly, then shut
down and seemed to be very fussy about the amount of load applied and DC
supply voltage too. All the waveforms look pretty good on my scope except
that across the 1 ohm current sense resistor - which showed a lot of
ringing at several MHz.

I even removed the ferrite transformer from the PCB to test it independently
and confirm it was OK.

Finally, I tried a 47nF cap directly across the 1 ohm resistor - which made
a big improvement to the behaviour. Smelling a fat rat, I removed the
resistor and broke it apart to find if it was really metal film - bingo !!

Although my resistor looked almost identical to the original, I had
accidentally swapped a film resistor for a wirewound type. It had about 12
turns of wire on the ceramic core instead of the 3 turn spiral a MF type
typically has so a tad more inductance.

Both resistors had near identical, smooth, light grey bodies with the same
coloured bands in exactly the same places - what a trap.

With a genuine MF type fitted, ringing was suppressed by about two thirds
and the SMPS finally worked as intended.



.... Phil

I worked at a pro audio company using wirewound power resistors to test
Class D power amps. I couldn't convince them to consider the reactance
effects at hypersonic frequencies, not only the switching artifacts but
the Power Factor Controllers too, create a rich VLF stew. It won't hurt
speakers but it may affect efficiency and heat load. Am I nuts?

unless these power resistors were very weird, as long tube shaped things
they'd still have less inductance than a speaker winding.

 

>"For the 1 ohm wire-wound sense resistor, the inductance was about 200nH.
However the ringing frequency was around 3MHz making the inductive reactance
almost 4 ohms - four times more than the value of the resistor !!! "

You twitwitted unsuccessful doppelganging lowlife untermention !

No idea of the parts you are putting in MY equipment ? No wonder they need consumer watchdogs organizations.

Actually I am just joking dude. If I had that problem, I would have found it btu likely it would take longer. they do not give you the specs on a print for the voltage across that usually. They CERTAINLY don't give you a spectrum ananlysis.

 

[Phil Allison]

"dave"

I worked at a pro audio company using wirewound power resistors to test
Class D power amps. I couldn't convince them to consider the reactance
effects at hypersonic frequencies, not only the switching artifacts but
the Power Factor Controllers too, create a rich VLF stew. It won't hurt
speakers but it may affect efficiency and heat load. Am I nuts?

** The lower the resistor's value, the more significant inductance becomes.

Egs:

I use a pair of 100W rated, 8 ohm, tubular, wire-wound resistors as a dummy
load - wired in series for 16 ohms and in parallel for 4 ohms. The ceramic
tube is about 1 inch dia and 4.5 inches long with 34 turns of flat strip
conductor would along it, so the inductance is about 6uH.

At 20kHz, the error caused by inductance is under 0.5% while at 100kHz, the
error is still only 10%.

For the 1 ohm wire-wound sense resistor, the inductance was about 200nH.
However the ringing frequency was around 3MHz making the inductive reactance
almost 4 ohms - four times more than the value of the resistor !!!


..... Phil

 

[John Robertson]

On 07/26/2014 10:21 PM, Phil Allison wrote:

** Hi,

recently I wasted much time trying to get a small, off-line SMPS to work
properly. The supply was part of a 1000W class D audio amplifier and built
onto the same PCB smothered in mostly SMD parts.

The design employed an 8 pin DIL chip (Infineon ICE 2A165) that did almost
everything and it along with some SMD diodes and two 1W resistors had
failed.

After replacing all the damaged parts - it would operate briefly, then shut
down and seemed to be very fussy about the amount of load applied and DC
supply voltage too. All the waveforms look pretty good on my scope except
that across the 1 ohm current sense resistor - which showed a lot of
ringing at several MHz.

I even removed the ferrite transformer from the PCB to test it independently
and confirm it was OK.

Finally, I tried a 47nF cap directly across the 1 ohm resistor - which made
a big improvement to the behaviour. Smelling a fat rat, I removed the
resistor and broke it apart to find if it was really metal film - bingo !!

Although my resistor looked almost identical to the original, I had
accidentally swapped a film resistor for a wirewound type. It had about 12
turns of wire on the ceramic core instead of the 3 turn spiral a MF type
typically has so a tad more inductance.

Both resistors had near identical, smooth, light grey bodies with the same
coloured bands in exactly the same places - what a trap.

With a genuine MF type fitted, ringing was suppressed by about two thirds
and the SMPS finally worked as intended.



..... Phil

Thanks for the tip - I've learned something today! Mind you most of the
stuff I deal with doesn't work in those frequencies, but still, good to
have in the back of one's mind when troubleshooting or installing
replacement parts in items like switching power supplies or other medium
to high (and RF of course) frequency things...

John :-#)#
--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[Trevor Wilson]

On 27/07/2014 3:21 PM, Phil Allison wrote:

** Hi,

recently I wasted much time trying to get a small, off-line SMPS to work
properly. The supply was part of a 1000W class D audio amplifier and built
onto the same PCB smothered in mostly SMD parts.

The design employed an 8 pin DIL chip (Infineon ICE 2A165) that did almost
everything and it along with some SMD diodes and two 1W resistors had
failed.

After replacing all the damaged parts - it would operate briefly, then shut
down and seemed to be very fussy about the amount of load applied and DC
supply voltage too. All the waveforms look pretty good on my scope except
that across the 1 ohm current sense resistor - which showed a lot of
ringing at several MHz.

I even removed the ferrite transformer from the PCB to test it independently
and confirm it was OK.

Finally, I tried a 47nF cap directly across the 1 ohm resistor - which made
a big improvement to the behaviour. Smelling a fat rat, I removed the
resistor and broke it apart to find if it was really metal film - bingo !!

Although my resistor looked almost identical to the original, I had
accidentally swapped a film resistor for a wirewound type. It had about 12
turns of wire on the ceramic core instead of the 3 turn spiral a MF type
typically has so a tad more inductance.

Both resistors had near identical, smooth, light grey bodies with the same
coloured bands in exactly the same places - what a trap.

With a genuine MF type fitted, ringing was suppressed by about two thirds
and the SMPS finally worked as intended.

**Yikes! Was it a WES resistor?


--
Trevor Wilson www.rageaudio.com.au

 

[Phil Allison]

"Trevor Wilson"

Phil Allison wrote:
** Hi,

recently I wasted much time trying to get a small, off-line SMPS to work
properly. The supply was part of a 1000W class D audio amplifier and
built
onto the same PCB smothered in mostly SMD parts.

The design employed an 8 pin DIL chip (Infineon ICE 2A165) that did
almost
everything and it along with some SMD diodes and two 1W resistors had
failed.

After replacing all the damaged parts - it would operate briefly, then
shut
down and seemed to be very fussy about the amount of load applied and DC
supply voltage too. All the waveforms look pretty good on my scope except
that across the 1 ohm current sense resistor - which showed a lot of
ringing at several MHz.

I even removed the ferrite transformer from the PCB to test it
independently
and confirm it was OK.

Finally, I tried a 47nF cap directly across the 1 ohm resistor - which
made
a big improvement to the behaviour. Smelling a fat rat, I removed the
resistor and broke it apart to find if it was really metal film - bingo
!!

Although my resistor looked almost identical to the original, I had
accidentally swapped a film resistor for a wirewound type. It had about
12
turns of wire on the ceramic core instead of the 3 turn spiral a MF type
typically has so a tad more inductance.

Both resistors had near identical, smooth, light grey bodies with the
same
coloured bands in exactly the same places - what a trap.

With a genuine MF type fitted, ringing was suppressed by about two thirds
and the SMPS finally worked as intended.


**Yikes! Was it a WES resistor?

*** Yep.

" 1W wirewound, low inductance type, KNP ....... "

Because it looked so similar, it was stored along with MF types. I actually
suspected the resistor pretty quickly, got another and tested it with my Bob
Parker ESR meter - it read spot on. I did a 200kHz square wave test too and
still missed it.

The particular SMPS operates at 100kHz while the ringing frequency is
3.5MHz - it has many outputs and runs ALL the low power electronics
including a valve !!

FYI:

it's internal to a Chinese " Ampeg SVT-7 pro" bass head, which has a
bridged pair of class D amps rated at 1000W into 4 ohms and a 1.2kW SMPS on
the same PCB as the small supply.

The original fault was a mid air arc-over between the leads of two 1W
resistors, spaced 8mm apart. So from +340VDC ( from the main SMPS's electro
bank ) to the IC end of the 1ohm sense resistor. Blew 200mm of 2mm wide
track right off the PCB, among all the other carnage.



..... Phil

 

I couldn't count all the times I ordered low value resistors and put on the page "NON INDUCTIVE". but rewally, just HOW non-inductive do I want it ?

Wire wound resistors already are wound with a bucking configuration. If you want a coil they make all the turns go the same way, if you want a resistor they do not.

Alot of times we were taliking equipment that was not really working at all that high a frquency. I have always been careful about components that go into decent audio equipment for example. I do not use ECGs or SKs or wahtever, which are fine for TV deflection circuits usuall, a few other things. But for the audio path I pay alot of attention to what I use.

But now this comes up. We knew it would happen. I mean we knew if you used a wirewound resistor in a certain application this might happen. What is jus a bit surprising is that the voltage eveloped across your resistor is not filtered. I see such designs and kinda wonder, do they really need this current response so fast that they can't use an integrator to smooth it out ? that method allows alot more configs for current limiting.

Of course that is not the trend anymore. there are SMPSes that damnear shut down in one cycle in case of a short. This of course allows them to avoid overbuilding them. Need 20 watts diddipation, get a 20.0001 watt device. that is engineering. You can't be a wasteful engineer - for long. None of my projects are ever likely to see a production line, but they will probably outlive the designer and builder.

But that's not what sells.

 

diddipation ? lol

dissipation of course

It's getting bad folks

 

[dave]

On 07/27/2014 11:57 AM, Cydrome Leader wrote:

dave <ricketzz@earthlink.net> wrote:

I worked at a pro audio company using wirewound power resistors to test
Class D power amps. I couldn't convince them to consider the reactance
effects at hypersonic frequencies, not only the switching artifacts but
the Power Factor Controllers too, create a rich VLF stew. It won't hurt
speakers but it may affect efficiency and heat load. Am I nuts?


unless these power resistors were very weird, as long tube shaped things
they'd still have less inductance than a speaker winding.

A very complex reactance anyway. The amps were ca 10KW 12KW bridged into
4 Ohm loads made of 8 Ohm cabs series parallel. There were a lot of
wirewound power resistors, in metal enclosures per OSHA, "switched" with
Banana plugs. I like the resistors you mount on heat sinks like power
transistors.

 

[dave]

On 07/28/2014 02:34 AM, Phil Allison wrote:

"Trevor Wilson"
Phil Allison wrote:
** Hi,

recently I wasted much time trying to get a small, off-line SMPS to work
properly. The supply was part of a 1000W class D audio amplifier and
built
onto the same PCB smothered in mostly SMD parts.

The design employed an 8 pin DIL chip (Infineon ICE 2A165) that did
almost
everything and it along with some SMD diodes and two 1W resistors had
failed.

After replacing all the damaged parts - it would operate briefly, then
shut
down and seemed to be very fussy about the amount of load applied and DC
supply voltage too. All the waveforms look pretty good on my scope except
that across the 1 ohm current sense resistor - which showed a lot of
ringing at several MHz.

I even removed the ferrite transformer from the PCB to test it
independently
and confirm it was OK.

Finally, I tried a 47nF cap directly across the 1 ohm resistor - which
made
a big improvement to the behaviour. Smelling a fat rat, I removed the
resistor and broke it apart to find if it was really metal film - bingo
!!

Although my resistor looked almost identical to the original, I had
accidentally swapped a film resistor for a wirewound type. It had about
12
turns of wire on the ceramic core instead of the 3 turn spiral a MF type
typically has so a tad more inductance.

Both resistors had near identical, smooth, light grey bodies with the
same
coloured bands in exactly the same places - what a trap.

With a genuine MF type fitted, ringing was suppressed by about two thirds
and the SMPS finally worked as intended.


**Yikes! Was it a WES resistor?

*** Yep.

" 1W wirewound, low inductance type, KNP ......."

Because it looked so similar, it was stored along with MF types. I actually
suspected the resistor pretty quickly, got another and tested it with my Bob
Parker ESR meter - it read spot on. I did a 200kHz square wave test too and
still missed it.

The particular SMPS operates at 100kHz while the ringing frequency is
3.5MHz - it has many outputs and runs ALL the low power electronics
including a valve !!

FYI:

it's internal to a Chinese " Ampeg SVT-7 pro" bass head, which has a
bridged pair of class D amps rated at 1000W into 4 ohms and a 1.2kW SMPS on
the same PCB as the small supply.

The original fault was a mid air arc-over between the leads of two 1W
resistors, spaced 8mm apart. So from +340VDC ( from the main SMPS's electro
bank ) to the IC end of the 1ohm sense resistor. Blew 200mm of 2mm wide
track right off the PCB, among all the other carnage.



.... Phil

Can't wait to see one of those. I fixed an SVT3Pro with fried
amplifier stage (everything north of the tube). Learned a few things.
That was over a year ago and it still works. Knock on MDF.

 

[Maynard A. Philbrook Jr.]

In article <4e8e6326-f526-448d-90dc-d69928275fd0@googlegroups.com>,
jurb6006@gmail.com says...

couldn't count all the times I ordered low value resistors and put on the page "NON INDUCTIVE". but rewally, just HOW non-inductive do I want it ?

There's a price to pay for film type R's that are low inductive,
they usually can't handle a very short high peak pulse. POP!

Carbon composite is just about the best in both worlds, they handle
transients and are not very inductive. We use these types for a
HV divider string from 2Mev down to a few uA for a reading. The signal
is at 100Khz so can't have induction there and also can't have the
R's popping when we get a now and then snap of voltage that causes a
short transient.

Jamie

 

[Phil Allison]

<jurb6006@gmail.com>

I couldn't count all the times I ordered low value resistors and put on the
page "NON INDUCTIVE".

**Only way to get that is to order carbon composition types.


Wire wound resistors already are wound with a bucking configuration.

** That is so rare I have never come across one.

If you want a coil they make all the turns go the same way, if you want a
resistor they do not.

** Fraid they do, resistors are nearly all coils - but it hardly ever
matters.


..... Phil

 

[Phil Allison]

"Phil Allison"

"Trevor Wilson"

FYI:

it's internal to a Chinese " Ampeg SVT-7 pro" bass head, which has a
bridged pair of class D amps rated at 1000W into 4 ohms and a 1.2kW SMPS
on the same PCB as the small supply.

The original fault was a mid air arc-over between the leads of two 1W
resistors, spaced 8mm apart. So from +340VDC ( from the main SMPS's
electro bank ) to the IC end of the 1ohm sense resistor. Blew 200mm of 2mm
wide track right off the PCB, among all the other carnage.

** See link to good pic of the insides of one:

http://www.talkbass.com/threads/nad-svt7-pro-also-comparing-it-to-my-streamliner-900.877128/page-3

Bottom of page, click on image to enlarge.

The high power SMPS uses just two TO220 pak IGBTs while the 1000W bridge amp
uses only four TO220 Mosfets.

There are no class D amp chips and the mode of operation of the output stage
is mysterious.



..... Phil

 

[N_Cook]

On 29/07/2014 00:40, Maynard A. Philbrook Jr. wrote:

In article <4e8e6326-f526-448d-90dc-d69928275fd0@googlegroups.com>,
jurb6006@gmail.com says...
couldn't count all the times I ordered low value resistors and put on the page "NON INDUCTIVE". but rewally, just HOW non-inductive do I want it ?




There's a price to pay for film type R's that are low inductive,
they usually can't handle a very short high peak pulse. POP!

Carbon composite is just about the best in both worlds, they handle
transients and are not very inductive. We use these types for a
HV divider string from 2Mev down to a few uA for a reading. The signal
is at 100Khz so can't have induction there and also can't have the
R's popping when we get a now and then snap of voltage that causes a
short transient.

Jamie

Just for short duration testing purposes I suppose, or back to the bad
old days of barbecue charcoal laying in wait, in sustained overload
situations

 

[Cydrome Leader]

dave <ricketzz@earthlink.net> wrote:

On 07/27/2014 11:57 AM, Cydrome Leader wrote:
dave <ricketzz@earthlink.net> wrote:

I worked at a pro audio company using wirewound power resistors to test
Class D power amps. I couldn't convince them to consider the reactance
effects at hypersonic frequencies, not only the switching artifacts but
the Power Factor Controllers too, create a rich VLF stew. It won't hurt
speakers but it may affect efficiency and heat load. Am I nuts?


unless these power resistors were very weird, as long tube shaped things
they'd still have less inductance than a speaker winding.

A very complex reactance anyway. The amps were ca 10KW 12KW bridged into
4 Ohm loads made of 8 Ohm cabs series parallel. There were a lot of
wirewound power resistors, in metal enclosures per OSHA, "switched" with
Banana plugs. I like the resistors you mount on heat sinks like power
transistors.

I hope you used special gold plated, cyogenic magical copper cables for
all that.

I just toured a plant that had gigantic resistor arrays mounted into what
appeared to be bread racks. All the resistors were sealed into oil filled
glass tubes, in house. Any like anything used on a shop floor, it had lots
of banana plugs, but with upto tens of thousands of volts across them when
energized. Each jack for each tap into the string was Dymo labelled. I
can't imagine how much it cost to make each one.

The really scary stuff was done in rooms with dented expaned metal cages.

 

[Cydrome Leader]

Phil Allison <phil_a@tpg.com.au> wrote:

"dave"

I worked at a pro audio company using wirewound power resistors to test
Class D power amps. I couldn't convince them to consider the reactance
effects at hypersonic frequencies, not only the switching artifacts but
the Power Factor Controllers too, create a rich VLF stew. It won't hurt
speakers but it may affect efficiency and heat load. Am I nuts?

** The lower the resistor's value, the more significant inductance becomes.

Egs:

I use a pair of 100W rated, 8 ohm, tubular, wire-wound resistors as a dummy
load - wired in series for 16 ohms and in parallel for 4 ohms. The ceramic
tube is about 1 inch dia and 4.5 inches long with 34 turns of flat strip
conductor would along it, so the inductance is about 6uH.

At 20kHz, the error caused by inductance is under 0.5% while at 100kHz, the
error is still only 10%.

For the 1 ohm wire-wound sense resistor, the inductance was about 200nH.
However the ringing frequency was around 3MHz making the inductive reactance
almost 4 ohms - four times more than the value of the resistor !!!

well, it's known that giant ceramic wire wound power resistors are not the
choice for RF use.

 

[Michael A. Terrell]

Cydrome Leader wrote:

well, it's known that giant ceramic wire wound power resistors are not the
choice for RF use.

Carborundum resistors are used for RF.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

 

[Phil Allison]

"Cydrome Leader"

Phil Allison

** The lower the resistor's value, the more significant inductance
becomes.

Egs:

I use a pair of 100W rated, 8 ohm, tubular, wire-wound resistors as a
dummy
load - wired in series for 16 ohms and in parallel for 4 ohms. The
ceramic
tube is about 1 inch dia and 4.5 inches long with 34 turns of flat strip
conductor would along it, so the inductance is about 6uH.

At 20kHz, the error caused by inductance is under 0.5% while at 100kHz,
the
error is still only 10%.

For the 1 ohm wire-wound sense resistor, the inductance was about 200nH.
However the ringing frequency was around 3MHz making the inductive
reactance
almost 4 ohms - four times more than the value of the resistor !!!

well, it's known that giant ceramic wire wound power resistors are not the
choice for RF use.

** Sure - but this is a current sense resistor in SMPS circuit where most
of the current is at 100kHz but with a strong harmonic at about 30 times
that frequency. Problem being, the over-current trip was being activated
prematurely because the peak value of that harmonic was being exaggerated by
a factor of 3.

While 1W metal film resistors have low enough inductance to work OK in the
circuit, typical wirewound types do not.

BTW:

I could have added a RC network ( ie a Zobel ) across the 1 ohm wirewound to
bring it line at 3MHz and well beyond. A 47nF cap and any 1 ohm, 0.5W film
type would do fine.

Same goes for the 100W 8 ohm power resistor, a Zobel using 68nF and 8.2 ohms
corrects it to beyond 5MHz if that was ever needed.


..... Phil