Maker Pro
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Bad cap topologies

D

D Yuniskis

Jan 1, 1970
0
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)
 
W

William Sommerwerck

Jan 1, 1970
0
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>
 
J

Jamie

Jan 1, 1970
0
D said:
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!

:)
 
W

William Sommerwerck

Jan 1, 1970
0
Meat Plow said:
On Mon, 17 Aug 2009 08:21:16 -0700, "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?
 
W

William Sommerwerck

Jan 1, 1970
0
Could add TO-18 style heat sinks to them!
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.
 
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 µF 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
 
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
 
W

William Sommerwerck

Jan 1, 1970
0
Meat Plow said:
On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck"
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!
 
M

Miguel Giménez

Jan 1, 1970
0
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
 
D

D Yuniskis

Jan 1, 1970
0
Hi PlainBill,


[much elided]
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 µF 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...
 
J

JW

Jan 1, 1970
0
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.
 
G

Geoffrey S. Mendelson

Jan 1, 1970
0
Dave said:
Don't be silly. Products with an unacceptable failure rate simply won't
sell. Especially components where there are alternative suppliers.

If only that were true. People often buy based soley upon price. Rarely
do you see the same product sold for more than a month or two, often
the replacement product has a different brand name.

Since you are in the UK look at the 10 quid DVD players ASDA sold a few
years ago. How many of them are still around? When they fail, how many people
go as far as buying a "cleaning disk" and using it instead of just throwing
it out?

I know we have different experience with cleaning disks, but it's a
positive action by a consumer to resolve the problem themselves instead
of just dumping it in the bin, no matter if it works or not, or does more
harm than good.

Here they go for between 100-150 NIS (16-24 UKP) due to taxes and overhead.
Now that we have entered the "digital age", people are replacing them with
"full HD" players that do image upscaling (aka faking it) which sell for
around 60 UKP.

With those prices it does not pay to make the trip to a repair shop and
certainly not to pay for a repair.

Geoff.
 
W

William Sommerwerck

Jan 1, 1970
0
Don't be silly. Products with an unacceptable failure rate simply won't
sell. Especially components where there are alternative suppliers.

So how does the Chinese company Lifetime stay in business?
 
G

Geoffrey S. Mendelson

Jan 1, 1970
0
William said:
So how does the Chinese company Lifetime stay in business?

Many Chinese component manufacturers don't sell to outside of China. The
companies that buy from them build a production run of a product and then
stop. They then move one to the next product. By the time they show up on
your shelf, it may be 3-6 months since they were produced, and several models
ago.

The manufacturer simply does not care, they don't take warranty returns. If the
unit price of a product is $50 and 1% are expected to fail, they sell the for
$48 (in reality they price them at $52 and sell them for $50). It's up to the
importer in your country to deal with returns.

In the case of large companies, they don't bother. A returned item is replaced
with a new (and probably later) one, and the old one gets thrown out or
recycled.

Small retailers do the same thing via their distributer or just trash them
depending upon the contract they have.

None of the units ever make it back to China, except in containers of recycled
goods for dumping.

This is nothing new, about 25 years ago I was very friendly with the number
one importer of "220" or "grey" goods on the east coast of the US. He would
take defective stuff back for repair, but could never keep a tech at what he
could afford to pay them. In the end the stuff just ended up in the trash and
the prices were raised enough to cover the losses.

I also read news stories in the past where major US retailers were keeping track
of people who returned goods and if you returned too many, they would not let
you return any more.

One US manufacturer of radios has a 30 day return for refund policy, but
won't sell you another radio if you return one.

Geoff.
 
Hi PlainBill,


[much elided]
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 µF 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...
It depends on your definition of 'a little time'. My primary source
of information is www.badcaps.net/forum It would appear you are at
least doubling the MTBF (mean time between failures) by using high
quality caps. That would mean if you replace the caps in a two year
old monitor, it will probably last an additional 4 years before it is
necessary to replace them again. At worst, that is a significant
improvement.

When I look at the cost, power consumption, clarity, and design of 4
year old LCD monitors vrs those one or two years old, I doubt that in
5 years you would be asked to repair many 7 year old monitors.

I would agree, having to redo the replacement every two years could
cause speculation about your skills.

PlainBill
 
D

D Yuniskis

Jan 1, 1970
0
Hi PlainBill,

On Mon, 17 Aug 2009 12:16:47 -0700, D Yuniskis
[snip]
[snip]
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...

It depends on your definition of 'a little time'. My primary source
of information is www.badcaps.net/forum It would appear you are at
least doubling the MTBF (mean time between failures) by using high
quality caps. That would mean if you replace the caps in a two year
old monitor, it will probably last an additional 4 years before it is
necessary to replace them again. At worst, that is a significant
improvement.

Agreed. Though, perhaps another way of combining my questions
would be: "Would a different design approach result in a
(much) longer life expectancy for this type of product?"
When I look at the cost, power consumption, clarity, and design of 4
year old LCD monitors vrs those one or two years old, I doubt that in
5 years you would be asked to repair many 7 year old monitors.

Most of the monitors I've been repairing are in the 2-3 year
old range. It's possible that older monitors have already
made their way to The Great Recycling Bin in the Sky. :-/
I would agree, having to redo the replacement every two years could
cause speculation about your skills.

I don't have a fragile ego! :> Rather, I am concerned as to
whether or not I am doing these people (read original post:
"a local non-profit") a *real* service or just buying them
"a little time". I.e., when I am no longer affiliated with
them -- and there is a high probability that they won't have
someone with my skillset available -- will they just see this
whole pattern repeat itself N months/years hence?

And, from a selfish perspective, what can *I* learn from these
failures to help me design products that don't exhibit them!
 
Hi PlainBill,

On Mon, 17 Aug 2009 12:16:47 -0700, D Yuniskis
[snip]
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?)
[snip]
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...

It depends on your definition of 'a little time'. My primary source
of information is www.badcaps.net/forum It would appear you are at
least doubling the MTBF (mean time between failures) by using high
quality caps. That would mean if you replace the caps in a two year
old monitor, it will probably last an additional 4 years before it is
necessary to replace them again. At worst, that is a significant
improvement.

Agreed. Though, perhaps another way of combining my questions
would be: "Would a different design approach result in a
(much) longer life expectancy for this type of product?"
When I look at the cost, power consumption, clarity, and design of 4
year old LCD monitors vrs those one or two years old, I doubt that in
5 years you would be asked to repair many 7 year old monitors.

Most of the monitors I've been repairing are in the 2-3 year
old range. It's possible that older monitors have already
made their way to The Great Recycling Bin in the Sky. :-/
I would agree, having to redo the replacement every two years could
cause speculation about your skills.

I don't have a fragile ego! :> Rather, I am concerned as to
whether or not I am doing these people (read original post:
"a local non-profit") a *real* service or just buying them
"a little time". I.e., when I am no longer affiliated with
them -- and there is a high probability that they won't have
someone with my skillset available -- will they just see this
whole pattern repeat itself N months/years hence?

And, from a selfish perspective, what can *I* learn from these
failures to help me design products that don't exhibit them!

Most power supplies I see already use inductors in the DC filters.
You are dealing with a trade off between the switching frequency,
transformer size, and capacitance. That usually results in a 'choose
two of the above' situation.

The only possible change that I am aware of is to use replacements
that have a polymer electrolyte. Frankly, you would be in a better
position to determine if that would be cost effective.

The discussion at badcaps indicates you can expect at least double the
life by using top grade caps. If you are repairing monitors 2-3 years
old, you can expect they will last 4-6 years more after the repair.
Assuming you would be still available to do your excellent repair
work, by that time I would expect a new equivalent monitor would cost
as much as repairing the existing monitor. At that point, repair is
pointless.

PlainBill
 
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