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rjnerd
User Rank
Iron
cutting one corner too many.
rjnerd   5/22/2012 7:14:45 AM
NO RATINGS
By any chance were the capacitors branded "LTEC".  If you have a TiVO HR10-250 (the HD DVR that DirecTV distributed)  eventually the thing will start reporting an intermittent overheat condition.  No, its not actually over temp, intstead one or both of the power supply capacitors that are filtering the 5v supply will have the self-same domed top.

Its happened to me on two of them, and if you peruse the Ebay listings of ones offered for parts, you will be sure to find one or two on offer that are also suffering the same problem.  A little time with a soldering iron, and some replacements with a higher temperature rating, and they are fine.

I did notice that the replacement units I bought were noticeably larger than the originals, it was a bit of a squeeze getting them in.  They are located inside an inverted U formed by two of the heat sinks.  They even have one of them in contact with the to-220 case of a switch transistor, and covered with a big blob of glue, that I am sure helps keep them from cooling (hence my grabbing the highest temp spec I could find).

Because the designer packed them in right next to the hottest components on the board, how much was the fault of the capacitor and how much was just due to years of a bake cycle (they don't have an off switch).

nauzad
User Rank
Silver
Re: cutting one corner too many.
nauzad   5/22/2012 9:01:31 AM
NO RATINGS
I dont remember the brand of capacitors on the board, but I replaced them with Nichikon.

naperlou
User Rank
Blogger
Re: cutting one corner too many.
naperlou   5/22/2012 9:06:22 AM
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This sounds like a common problem with electronics and I think it must be the components. 

I was at the CompUSA warehouse (my son and I go there often).  We are lucky to have this nearby.  The store front is like a factory outlet.  We were looking at building a server, so I was looking at motherboards.  All of them seemed to have a claim that they used Japanese capicators of a certain type.  I wondered at this, since most were made in Taiwan.  After asking around I found that there had been a rash of failures of motherboards a while back, and the cause was cheap capicators.  Sounds like Acer did not get the memo. 

Isn't it interesting that something so basic as a capicator (and its placement) can cause so many problems?

tekochip
User Rank
Platinum
No derating?
tekochip   5/22/2012 9:51:39 AM
NO RATINGS
Do you know the voltage rating on the caps? I wonder if they were pushing them at the edge of the specification with no derating, you know a 6V capacitor on a 6V circuit.


Nancy Golden
User Rank
Platinum
Internet for Troubleshooting
Nancy Golden   5/22/2012 10:39:25 AM
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Looks like you did a great job - that is one thing I love about the advent of the internet. It has become a valuable resource for troubleshooting. I have had issues from my video camera to my garage door opener and plugging in the problem has brought not only answers, but video demonstrations for the fix on You Tube! I love it when it is as simple as replacing a cap or two. I would have thought the same thing - that there may be something causing the caps to blow. But even if it isn't a matter of cheap materials but heat stress or some such thing that becomes an issue over time - at least you'll know what to do. Hopefully Acer has caught on and fixed the problem. It's funny - when I called Sony about the defect occurring with my video camera, they said they had no prior knowledge of that type of failure - yet a simple search on the internet indicated at least fifty or so other folks experiencing the same issue!

rjnerd
User Rank
Iron
Re: No derating?
rjnerd   5/22/2012 10:44:42 AM
NO RATINGS
Its a 5v circuit, and the cap is labeled 6.3 volts.

nauzad
User Rank
Silver
Re: cutting one corner too many.
nauzad   5/22/2012 1:44:48 PM
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Just looked up some old references. The caps originally on the board were CapXon's rated to 85ºC if I recollect correctly.

Rob Spiegel
User Rank
Blogger
Re: cutting one corner too many.
Rob Spiegel   5/22/2012 2:19:05 PM
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This makes me wonder whether the components that failed were counterfeit. Counterfeits can be disguised very well these days. Counterfeit components woud certainly explain the high failure rates Naperlou describes.

pcan
User Rank
Iron
Re: cutting one corner too many.
pcan   5/22/2012 4:25:32 PM
NO RATINGS
On a previous job, I worked in the technical department of a importer of LCD TV's and computer monitors. The computer monitor product line was manufactured by a well known Taiwan OEM manufacturer with good reputation and big name clients, and branded with our company logo. Technical documentation, EMC test and product samples - everything was perfectly fine. After 8 months and truckloads of monitors already sold, the number of field returns started to rise. In the summer, it became a deluge; almost every single monitor broke on the field. The power supply had faulty capXon electrolytic capacitors. On closer examination, the power supply design turned out to be questionable. The faulty capacitors were extremely close to heat spreaders, and they produced high amount of heat themselves. They may have worked well in a traditional full bridge power supply, but certainly not in a high-frequency switched mode power supply. A comparison to the schematic diagram of the switched mode controller chip revealed that the power supply manufacturer removed all the current limiting components except the main safety fuse, and substituted a 1000V rectifier diode with a 200V rectifier. The result: a minor power surge or the increased load caused by the degrading capacitors would open the safety fuse. This was supposedly a quality product from a reputable supplier. The company management was so upset that completely abandoned this market and closed down the business unit. The last container full of soon-to-be broken monitors was sold at scrap price to a broker that shipped them to central Africa. We enclosed a courtesy gift: a box full of quality replacement capacitors and complete instructions for the rework. I keeped for internal company use about 50 monitors. After replacing the capacitors, they still work after almost 5 years.

Tim
User Rank
Platinum
Re: cutting one corner too many.
Tim   5/22/2012 7:23:03 PM
NO RATINGS
I like the idea of the care package for the end user. I once purchased a DIY bookshelf that contained two hardware kits and a note that read to only use the one specially marked hardware package because the screws were a better design. The rework for the faulty screws was open the box and add a new bag and a note then retape the box and hope for the best.

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