Bad cap topologies

[D Yuniskis]

Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

 

[Meat Plow]

On Mon, 17 Aug 2009 06:22:49 -0700, D Yuniskis
<not.going.to.be@seen.com>wrote:

Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

So the caps should be moved to a cooler location?

 

[William Sommerwerck]

So the caps should be moved to a cooler location?

Yes, you hang them from really long leads so there's plenty of air
circulating around them. <broad grin>

 

[Jamie]

D Yuniskis wrote:

Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)
Answer is simple:

Built in obsolescence.!

Nothing like market research to keep the US dollars poring into China!

 

[Meat Plow]

On Mon, 17 Aug 2009 08:21:16 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

So the caps should be moved to a cooler location?

Yes, you hang them from really long leads so there's plenty of air
circulating around them. <broad grin

Could add TO-18 style heat sinks to them!

 

[William Sommerwerck]

"Meat Plow" <meat@petitmorte.net> wrote in message
news:328j13.pcb.17.1@news.alt.net...

On Mon, 17 Aug 2009 08:21:16 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net>wrote:

So the caps should be moved to a cooler location?

Yes, you hang them from really long leads so there's
plenty of air circulating around them. <broad grin

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat the capacitor's
internal resistance? Or is it ambient?

 

[Meat Plow]

On Mon, 17 Aug 2009 09:31:13 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

"Meat Plow" <meat@petitmorte.net> wrote in message
news:328j13.pcb.17.1@news.alt.net...
On Mon, 17 Aug 2009 08:21:16 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net>wrote:

So the caps should be moved to a cooler location?

Yes, you hang them from really long leads so there's
plenty of air circulating around them. <broad grin

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat the capacitor's
internal resistance? Or is it ambient?

Welp they heat from both external and internal but increasing the
surface area would theoretically be an advantage would it not?

 

[William Sommerwerck]

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat
the capacitor's internal resistance? Or is it ambient?

Welp they heat from both external and internal but increasing the
surface area would theoretically be an advantage would it not?

If you were trying to dissipate internal heat, yes. But if the environment
were the problem, you might be simply increasing the area available to pick
up heat.

 

[Meat Plow]

On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat
the capacitor's internal resistance? Or is it ambient?

Welp they heat from both external and internal but increasing the
surface area would theoretically be an advantage would it not?

If you were trying to dissipate internal heat, yes. But if the environment
were the problem, you might be simply increasing the area available to pick
up heat.

Ok then scrap the TO-18 sinks. How about individual Peltier coolers
for each cap?

 

On Mon, 17 Aug 2009 06:22:49 -0700, D Yuniskis
<not.going.to.be@seen.com> wrote:

Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

There are a number of factors involved.

1. Poor quality capacitors.

2. High surge currents found in SMPS and the backlight inverter

3. Proximity to heat producing components, chiefly heat sinks

4. Poor ventilation of the electronics portion of the monitor.

Because of the current manufacturing / distribution pattern, there is
limited feedback from consumer to designer. Still, the designs of LCD
monitors continue to evolve. A few years ago a 5V 4A power supply was
common. Today the 5V supply is less than half that. The monitor
logic card is being integrated into the LCD panel electronics, further
reducing component count and cost, and improving reliability. With
LED based backlight systems power demands will drop further.

As far as existing monitors, my recommendation is to replace all caps
(except the 150 ľF 450 Volt one) with good brand low ESR parts. My
personal preference is Panasonic FM and FC series', but others have
equivalent success with Rubycon and Nichicon.

PlainBill

 

On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat
the capacitor's internal resistance? Or is it ambient?

Welp they heat from both external and internal but increasing the
surface area would theoretically be an advantage would it not?

If you were trying to dissipate internal heat, yes. But if the environment
were the problem, you might be simply increasing the area available to pick
up heat.

But a capacitor will eventually reach the temperature of the

surrounding air. If it takes 5 minutes or 50 minutes the difference
is insignificant for a monitor that is on for 8 hours a day.

The solution is to improve air circulation.

PlainBill

 

[none]

D Yuniskis wrote:

Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

I can only offer a rumor about a manufacturer of electrolytic
capacitors. The story goes, a major well-known corporation was
developing a physically smaller, less expensive capacitor. They had a
prototype, which design was stolen and began appearing in the
cheap-parts market. The prototype was flawed, so the cheap parts are
similarly flawed.

As an aside to this tale, I can positively say the surface-mount
electrolytic capacitors used in a series of Panasonic DVC Pro video
recorders have an extraordinarily high failure rate.

Shops have opened up specializing in capacitor replacement for those
machines. A complete re-cap can go for $3,000 US.

You would probably have the best results replacing defective caps with,
as you say, better quality ones from reputable vendors.

The following borders upon superstition, but I'll include it:
If you have to choose between two electrolytic capacitors of the same
ratings, and both will fit the application despite one being physically
larger... I'd suggest buying the larger one. It will at least have more
heat-dissipation capacity.

 

[William Sommerwerck]

"Meat Plow" <meat@petitmorte.net> wrote in message
news:328osh.st5.19.3@news.alt.net...

On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net>wrote:

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat
the capacitor's internal resistance? Or is it ambient?

Welp they heat from both external and internal but increasing the
surface area would theoretically be an advantage would it not?

If you were trying to dissipate internal heat, yes. But if the
environment
were the problem, you might be simply increasing the area available to
pick
up heat.

Ok then scrap the TO-18 sinks. How about individual Peltier coolers
for each cap?

Hey... ultra-high-tech is the only way to go!

 

[William Sommerwerck]

"Meat Plow" <meat@petitmorte.net> wrote in message
news:328osh.st5.19.3@news.alt.net...

On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net>wrote:

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat
the capacitor's internal resistance? Or is it ambient?

Welp they heat from both external and internal but increasing the
surface area would theoretically be an advantage would it not?

If you were trying to dissipate internal heat, yes. But if the
environment
were the problem, you might be simply increasing the area available to
pick
up heat.

Ok then scrap the TO-18 sinks. How about individual Peltier coolers
for each cap?

Hey... ultra-high-tech is the only way to go!

 

[Miguel Giménez]

none escribió:

I can only offer a rumor about a manufacturer of electrolytic
capacitors. The story goes, a major well-known corporation was
developing a physically smaller, less expensive capacitor. They had a
prototype, which design was stolen and began appearing in the
cheap-parts market. The prototype was flawed, so the cheap parts are
similarly flawed.

You can read the complete story here: en.wikipedia.org/wiki/Capacitor_plague

--
Regards
Miguel Giménez

 

[D Yuniskis]

Hi PlainBill,

PlainBill47@yahoo.com wrote:

On Mon, 17 Aug 2009 06:22:49 -0700, D Yuniskis
not.going.to.be@seen.com> wrote:

[much elided]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

There are a number of factors involved.
1. Poor quality capacitors.

Yes, as I mentioned in my original post. But, my question
is intended to address the *expected* results if "good"
quality capacitors are used in the same circuit topologies.
I.e., will they also exhibit similar failure modes -- just
further down the road? (i.e., what is it about the topology
that causes the failures)

2. High surge currents found in SMPS and the backlight inverter

I.e., caps that handle the large ripple currents.

3. Proximity to heat producing components, chiefly heat sinks

Yes, but this doesn't seem to be as reliable a predictor of
failure. Often there are caps literally *touching* parts
that run VERY hot; yet they don't appear to fail as often
as other parts "free standing" (i.e., nothing within an inch!)
elsewhere in the circuit.

4. Poor ventilation of the electronics portion of the monitor.

Again, that would tend to affect every component in the
circuit (roughly) equally. No doubt it is a contributing
factor -- no doubt alol of the above are contributing
factors!

Because of the current manufacturing / distribution pattern, there is
limited feedback from consumer to designer. Still, the designs of LCD
monitors continue to evolve. A few years ago a 5V 4A power supply was
common. Today the 5V supply is less than half that. The monitor
logic card is being integrated into the LCD panel electronics, further
reducing component count and cost, and improving reliability. With
LED based backlight systems power demands will drop further.

As far as existing monitors, my recommendation is to replace all caps
(except the 150 ľF 450 Volt one) with good brand low ESR parts. My
personal preference is Panasonic FM and FC series', but others have
equivalent success with Rubycon and Nichicon.

I've been using the Panny parts as (historically) they have been
"very good to me" :> But, I ownder if I am just buying a little
more time before similar failures remanifest.

And, as a *designer*, I am interested in determining the real
cause of the problem(s) to ensure that I don't repeat these
problems in my own designs...

 

[Michael A. Terrell]

Meat Plow wrote:

On Mon, 17 Aug 2009 06:22:49 -0700, D Yuniskis
not.going.to.be@seen.com>wrote:

Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

So the caps should be moved to a cooler location?

Not a good idea. The added inductance and resistance of the leads
will cause problems. Why bother with low ESR electrolytics if you make
them useless?


--
You can't have a sense of humor, if you have no sense!

 

[Wild_Bill]

Generally, equipment made in Taiwan (electronic or machine types) are much
better quality than similar equipment made in China, IMO.
There are likely to be instances of circuit boards manufactured in China,
which are then assembled into a finished product elsewhere (Taiwan, USA or
other) which are no better than the Chinese equivalents though.
IMO, the only difference between a good and bad poduct, is if the
manufacturer designs and produces with a conscience.. not many operate in
this way, with very little or no quality control built into their production
facilities.

Looking at capacitor manufacturers' specifications will generally indicate
why even good quality capacitors fail. The bottom line is that the caps
aren't rated to meet aerospace or military ratings. Most quality
electrolytics have a rating of 2000 hours when properly placed on a board,
not beside a 5W power resistor in a heated area with very poor ventilation.
Equipment and even individual component design specs don't include
manufacturing defects or design changes, and most every product made today
has an attached disclaimer of: specifications subject to change without
notice.

When discount store consumer equipment lasts more than 2 years, that's about
the best that can be expected, depending upon the type/level of usage and/or
abuse.
For service that would be comparable to commercial use, one should buy
better equipment than the retail stores have to offer, or expect to pay the
equivalent cost of high grade equipment, by replacing cheaper equipment.
I know there are many exceptions that have lasted far longer than 2 years,
but they were typically made when manufacturing standards were higher than
today.

A better time to evaluate/examine equipment internally, would be before it's
put into service, instead of when it quits working.
If the internal design looks badly done, put the device at an unimportant
station, give it away to a employee (or raffle), or just sell it.
There are businesses that can provide testing and failure analysis for
electronic equipment.

Making equipment more compact leaves little space for airflow and/or heat
dissipation. Power supplies used to be separated from most of the signal
sections.
In new equipment, about the only time bare board is seen is when it's in the
lower priced version of that particular model, with less features, so some
components have been omitted.
I looked at a Acer 15.5" PC LCD monitor at a store yesterday that was about
as thick as 2 or 3 common paper tablets, and the PSU was internal.

As mentioned before, from a repair/servicing standpoint, one should only buy
quality components from a distributor that maintains a fresh inventory
direct from the manufacturer.
Not buying replacement caps in great quantities which will just sit in a
drawer for a year, should ensure that they won't start to develop faults
before they're installed.
Old stock electrolytics are likely to be inferior products. Many quality
brands of electrolytics are marked with date codes.

I've wonder how many technicians actually test new electrolytics before
installing them. Excessive internal leakage, for example, is as serious a
fault as high ESR.

--
Cheers,
WB
..............


"D Yuniskis" <not.going.to.be@seen.com> wrote in message
news:h6blfp$se4$1@aioe.org...

Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

 

[JW]

On Mon, 17 Aug 2009 13:17:33 -0400 Meat Plow <meat@petitmorte.net> wrote
in Message id: <328osh.st5.19.3@news.alt.net>:

On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net>wrote:

Could add TO-18 style heat sinks to them!

Might not that make things worse? Is the source of the heat
the capacitor's internal resistance? Or is it ambient?

Welp they heat from both external and internal but increasing the
surface area would theoretically be an advantage would it not?

If you were trying to dissipate internal heat, yes. But if the environment
were the problem, you might be simply increasing the area available to pick
up heat.


Ok then scrap the TO-18 sinks. How about individual Peltier coolers
for each cap?

Don't forget to remove the plastic cover surrounding the cap. That's got
to be good for a few degrees C.

 

[Dave Plowman (News)]

In article <grnim.552835$6p1.258480@en-nntp-02.dc1.easynews.com>,
Wild_Bill <wb_wildbill@XSPAMyahoo.com> wrote:

not many operate in this way, with very little or no quality control
built into their production facilities.

Don't be silly. Products with an unacceptable failure rate simply won't
sell. Especially components where there are alternative suppliers.

--
*Never underestimate the power of stupid people in large groups.

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.