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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Bad cap topologies
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) |
#2
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Bad cap topologies
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 |
#3
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Bad cap topologies
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! |
#4
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Bad cap topologies
"Meat Plow" wrote in message
... On Mon, 17 Aug 2009 08:21:16 -0700, "William Sommerwerck" 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? |
#5
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Bad cap topologies
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. |
#6
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Bad cap topologies
On Mon, 17 Aug 2009 06:22:49 -0700, 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) 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 |
#7
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Bad cap topologies
On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck"
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 |
#8
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Bad cap topologies
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. |
#9
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Bad cap topologies
"Meat Plow" wrote in message
... On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck" 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! |
#10
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Bad cap topologies
"Meat Plow" wrote in message
... On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck" 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! |
#11
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Bad cap topologies
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 he en.wikipedia.org/wiki/Capacitor_plague -- Regards Miguel Giménez |
#12
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Bad cap topologies
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#13
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Bad cap topologies
Meat Plow wrote: On Mon, 17 Aug 2009 06:22:49 -0700, 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) 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! |
#14
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Bad cap topologies
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" wrote in message ... 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) |
#15
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Bad cap topologies
On Mon, 17 Aug 2009 13:17:33 -0400 Meat Plow wrote
in Message id: : On Mon, 17 Aug 2009 09:50:56 -0700, "William Sommerwerck" 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. |
#16
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Bad cap topologies
In article ,
Wild_Bill 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 London SW To e-mail, change noise into sound. |
#17
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Bad cap topologies
Dave Plowman (News) wrote:
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. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM |
#18
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Bad cap topologies
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? |
#19
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Bad cap topologies
William Sommerwerck wrote:
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? 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. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM |
#20
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Bad cap topologies
In article ,
Geoffrey S. Mendelson wrote: 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. But those buying components for a manufacturer ain't 'people'. They will expect only a tiny number of failures from that component - anything else would be a nonsense. Given the number of different components in the average piece of consumer electronics. Which means the component makers must have decent quality control. 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? Dunno. Cheap electronics from the major UK supermarkets ain't worth having. Go to Lidl or Aldi for such things - they are miles better. The Germans obviously expect more. 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. Labour rates mean repairing many consumer goods ain't worth it, commerically. And, of course SM components. ;-) -- *No sentence fragments * Dave Plowman London SW To e-mail, change noise into sound. |
#21
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Bad cap topologies
Although I neglected to make it clear, I was commenting on the lack of
quality control in production of finished electronic gear, namely consumer electronic gear. For medical or avionics equipment there are very likely to be numerous levels of quality control, from testing of incoming components to rigorous testing of the finished products. For portable CD players that retail for less than $10, I seriously doubt that any QC exists. The components are most likely selected/chosen as whatever is cheapest/on sale that week. Many manufacturers are thinking in terms of the Harbor Freight business model. The products are built at the cheapest price point, and the ones that fail soon (or fail to work) are cheerfully replaced with another one. The failed units get sold off in bulk to someone else who might try to salvage/refurbish a number of working products from the failed ones, and/or just separate the materials and sell them as scrap. As someone else mentioned, when a product fails prematurely, the consumer may choose another brand for the next purchase, which very likely could have been made by the same manufacturer, but with a different brand name on it. The last time I looked, the supply of refurbished equipment was ample, but there are no profits to be made from refurbing those $10 CD players. They're just filler for the landfills, like so many other consumer goods produced presently. Refurbishing is relatively expensive due to transportation costs, repairing, repackaging and redistribution. -- Cheers, WB .............. "Dave Plowman (News)" wrote in message ... In article , Wild_Bill 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 London SW To e-mail, change noise into sound. |
#22
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Bad cap topologies
On Mon, 17 Aug 2009 12:16:47 -0700, D Yuniskis
wrote: Hi PlainBill, wrote: On Mon, 17 Aug 2009 06:22:49 -0700, D Yuniskis 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 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 |
#24
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Bad cap topologies
In article ,
Wild_Bill wrote: lthough I neglected to make it clear, I was commenting on the lack of quality control in production of finished electronic gear, namely consumer electronic gear. Oh there I'd agree. It is cheaper simply to replace faulty units than test each and every one fully before dispatch. However there will still be quality control as no profit will be made if the failure rate is too high. But that quality control could well consist of just insisting the component parts are to a standard. -- *Sorry, I don't date outside my species. Dave Plowman London SW To e-mail, change noise into sound. |
#25
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Bad cap topologies
On Tue, 18 Aug 2009 21:23:23 -0700, D Yuniskis
wrote: Hi PlainBill, wrote: 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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Bad cap topologies
On Aug 18, 5:27*pm, wrote:
... *My primary source of information iswww.badcaps.net/forum*It would appear you are at least doubling the MTBF (mean time between failures) by using high quality caps. Logically, that should be "at most doubling the MTBF"; remember that failures can include leaking of corrosive goo and short-circuiting. It's not surprising that 'badcaps.net' overemphasizes capacitor quality issues, but my ire is drawn rather to the mechanical design decisions that put the tiniest available capacitors onto a circuit board with zero clearance to adjacent components. An old design criterion was 'one amp ripple current to one square inch of surface area' for the purpose of dissipating the inevitable heat buildup. Empty space is GOOD. Don't minimize it! To get extra operational margins, it's useful to go to the next larger size of capacitor (in the case of tight-packed capacitors, that has to be longer case sizes, because bigger diameters won't fit). In theory, capacitors (like semiconductors and inductors) can benefit from heatsinking. Has anyone tried it? |
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