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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue Nov 17, 2009 6:24 pm Post subject: |
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Ok, today hopefully we're going to learn something that applies to real world scenarios. I recommend reading through this carefully so yo understand it. Again, I'll try to explain it so everyone can understand it.
| Ile wrote: |
So it must be ripple current that have killed these 85C caps in many medium hour Barco smps.
http://www.curtpalme.com/docs/Barco_FSB04_SMPU_Capacitor_Upgrade.pdf
It can't be ambient temp, because these are next to 120mm fan.
They learned they lesson and later models like 1209s have those caps listed as 105C in part list. Not sure if boards actually have 105C (subcontracted?), but least they updated documents. |
It was this post by Ile that encouraged my to write the last post on applied voltage vs rated voltage. After looking over the service bulletin my thoughts were part of it made sense and part of it didn't. I would agree, after looking over the schematics that these 2 caps may be subjected to higher ripple current and could be the cause of early failure but the solution in the bulletin did NOT make sense. Sure maybe a higher temperature cap may last longer but would still have higher current and would also eventually fail prematurely. Its like putting a band-aid on it.
Now I had my suspicions here but need to do some investigation to confirm it. Remember, I'm trying to avoid just opinion here.
So I began looking over the various model schematics along with certain datasheets and there it was. The confirmation of my suspicions.
Now remember my post on the house wiring and if you try to draw to much current through the wire, it will run hot. And the only way to solve it was to run a larger wire. SO think of these caps as the wire. Now they are running hot causing premature failure so something has to be changed. Now the bulletin says change to a 105C cap. The problem is this doesnt address the higher current so even the 105C would be running hot. It would maybe only last longer because its designed to last longer at a higher temp. But its really only 20 degrees C better which is really not that much.
SO what I found was in the early 808s schematic they used a 100uf/25v 85C cap. In the newer 1208s and 1209s they used a 100uf/50v 105C cap. As you can see they increase the voltage of the cap from 25v to 50v.
THIS WAS ACTUALLY THE SOLUTION.
However the bulletin makes no mention of the voltage increase. So even if you replace the original 100uf/25v 85C caps with 100uf/50v 85C cap, the problem would be solved. The higher temp rating is only an extra little gift for longevity.
I also found that the bulletin has an error in it. The bulletin states the 2 caps to have a location id of C104 and C114. The caps is question are actually C105 and C114.
So what we have in the end here is a very poorly written bulletin.
1: Has an error in it.
2: Makes no mention of the voltage increase of the caps which is more important the the temp rating.
So if you were to replace the original caps with with 100uf/25v 105C without knowing of the suggested voltage increased capacitor then you would still have a problem with the caps failing prematurely.
This can be applied anywhere there is a higher ripple current causing high core temp in a cap. Increase the voltage rating to handle the higher current.
Hope you enjoyed this one. 
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Ile
Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland
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| Posted: Tue Nov 17, 2009 9:09 pm Post subject: |
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| macgyver655 wrote: | So if you were to replace the original caps with with 100uf/25v 105C without knowing of the suggested voltage increased capacitor then you would still have a problem with the caps failing prematurely.
This can be applied anywhere there is a higher ripple current causing high core temp in a cap. Increase the voltage rating to handle the higher current.
Hope you enjoyed this one. |
Thanks I enjoyed it.
I was wondering those wrong names also, so I have chanced all those fife 100uF in primary side to 100uF 35-50V 105C in all my Barcos.
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jask
Joined: 17 Mar 2006
Posts: 10187
Location: kamloops BC
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| Posted: Wed Nov 18, 2009 2:57 am Post subject: |
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I have been REALLY enjoying this "class" proffessor Mac!! and it is particularly timely and relevant as the failure Ile brought up is exactly what happened to my 1208/2.
A couple of points; The Barco manual is full of mislabels the c100 transistor is labeled c101 and c141 on subsequent pages in my manual. I have no doubt ripple was a contributor,but would love to scope a well set up unit and then ramp up focus or geometry to see how it impacts ripple.
As an aside for Barco owners; loss of this transistor can leave +17v,while killing the 300v side...resulting in all the green lights being on-scan fail off,and no HV.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Wed Nov 18, 2009 3:29 pm Post subject: |
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Well we've discussed alot of different things that affect capacitors. Is there anything else left? Or are we at the end?
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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| Posted: Wed Nov 18, 2009 4:21 pm Post subject: |
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How about the benefits of lower ESR in a circuit or if it really makes no difference. or if some will benefit and some it would make it worse? I always get a bit confused here as I always assumed ESR always helps, but then a while ago i ran across something somewhere that said it could be bad in some instances. I just can't find the info i read on it.
Athanasios
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Nov 19, 2009 1:18 am Post subject: |
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I wasn't sure of how much I was going to get involved in ESR because high ESR is more of an effect then a cause, meaning high ESR doesn't cause cap failure it is an effect of a failing cap. But low esr caps could be an interesting topic. If I were to go into this then I would have to write a fairly large post. This one is one of the most difficult to understand but once it hits you, you'll get it.
So I'll tell you what. If 5 or more people post that they want me to go into ESR then I will.
Let the class speak!!!!!!! 
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Sparky015
Joined: 12 May 2009
Posts: 1185
Location: Cleveland / Akron, OH
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| Posted: Thu Nov 19, 2009 1:48 am Post subject: |
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I agree with Nash, I think this will be a nice way to round out this thread as a capacitor tutorial 101.
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jask
Joined: 17 Mar 2006
Posts: 10187
Location: kamloops BC
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| Posted: Thu Nov 19, 2009 4:07 am Post subject: |
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definitely ESR ( vote #2 here..) and that should lead back to ripple and ESR, high vs low ESR..... and RMS, inductive *reactance*, *capacitive reactance*, frequency power dissipation... 
this could be one of the best threads all year!!
edit:
Nash
Sparky
Me
need two more 
edit: for terminology..
Last edited by jask on Thu Nov 19, 2009 5:00 am; edited 1 time in total
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Nov 19, 2009 4:55 am Post subject: |
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| jask wrote: | definitely ESR ( vote #2 here..) and that should lead back to ripple and ESR, high vs low ESR..... and RMS, inductive capacitance, reactive capacitance, frequency power dissipation...
this could be one of the best threads all year!!
edit:
Nash
Sparky
Me
need two more |
Maybe you'd like to write a little something to start us off Jask.... 
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AnalogRocks
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Joined: 08 Mar 2006
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| Posted: Thu Nov 19, 2009 4:57 am Post subject: |
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ESR Extra sensory response? What's it stand for?
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jask
Joined: 17 Mar 2006
Posts: 10187
Location: kamloops BC
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| Posted: Thu Nov 19, 2009 5:07 am Post subject: |
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| macgyver655 wrote: | | jask wrote: | definitely ESR ( vote #2 here..) and that should lead back to ripple and ESR, high vs low ESR..... and RMS, inductive capacitance, reactive capacitance, frequency power dissipation...
this could be one of the best threads all year!!
edit:
Nash
Sparky
Me
need two more |
Maybe you'd like to write a little something to start us off Jask.... |
I just edited my post for the second time... carry on. 
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Ile
Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland
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| Posted: Thu Nov 19, 2009 9:20 am Post subject: |
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| macgyver655 wrote: | | If 5 or more people post that they want me to go into ESR then I will. |
Go for it.
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Nashou66
Joined: 12 Jan 2007
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Location: West Seneca NY
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Joe L.
Joined: 02 Jul 2007
Posts: 13
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| Posted: Thu Nov 19, 2009 2:28 pm Post subject: |
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When I repaired my Barco power supply I checked the ESR of the 100mfd cap I had replaced. It measured 12 ohms. It should be around one or two tenths of an ohm.
It was not allowing effective drive to the switching transistor it fed, causing the transistor to not turn on fully, and as a result it dissipated a lot more heat, resulting in the switching transistors failure (and that in turn took out the IC that feeds it too, and the fuse).
Yes, talk about ESR... You are now up to 5, unless the time limit expired... 
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dturco
Joined: 06 Feb 2009
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Location: Eastern Shore Maryland
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| Posted: Thu Nov 19, 2009 3:41 pm Post subject: |
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Where was this 5 minute post? All I see is a request for 5 people for Mac to continue. I have found this very interesting although it's not going to help me, I'm sure it will help many others.
So Mac, please continue.
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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| Posted: Thu Nov 19, 2009 5:46 pm Post subject: |
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| dturco wrote: | Where was this 5 minute post? All I see is a request for 5 people for Mac to continue. I have found this very interesting although it's not going to help me, I'm sure it will help many others.
So Mac, please continue. |
Oooops!! my bad, your right. Yeah this will be a good lesson.
I think I'll bring an apple for the teacher this class lesson.
I have another topic I want to get Rons opinion on as this guy gets blocked for his radical views on SRF.
Look up Ivor Cat this is what i am curious about http://www.ivorcatt.com/2603.htm
Athanasios
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Nov 19, 2009 6:35 pm Post subject: |
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Alright. I'll continue in a little while. Its to nice of a day here to be inside writing.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Nov 19, 2009 11:03 pm Post subject: |
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Alright. Before we move on there are a few things I want to address. I'm going to use some images to explain.
First we have an image of an Ampro SMPS (thanks Curt) that has some damage.
As you can see we have some damaged caps. Now the question is did they vent because they wore out or did something else cause them to vent. If we turn over the supply we see:
Definitely some damaged. So more then likely we have something else going on so I checked the rectifier at that location and sure enough it is shorted. More then likely one of the mosfets is was also bad. A quick test and sure enough the one remaining mosfet was shorted also.
So the question is did the mosfet fail causing the rectifier to fail and then overload the caps causing them to vent? Or were one or both caps failing, causing the rectifier to fail and in turn causing the mosfet to fail.
The answer is.......... I have no idea. At this point the caps cannot be tested so the true nature of the failure would never be known.
But what I will point out is in this pic....
As you can see, all those rectifiers have heatsinks attached and they are all grouped together giving off heat like little heaters. And also in that group are a bunch of capacitors, probably being over heated. So the manufacturer in an attempt to make a small compact supply, which would be easy to change in the field, compromised the design. Also the manufacturer usually only has regards for a limited life of the supply and if its meets that senario, then its deemed exceptable.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Thu Nov 19, 2009 11:20 pm Post subject: |
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In a continuation from my last post, that was a senario in which we have no control. But, are there things that we do have control over. The answer is yes. Lets start with this pic:
If you look where I have circled you see a resistor and 2 caps. Now when you have larger wattage resistor and they are up off the board it usually means its runs hot. These resistor sometimes run so hot you'll burn your finger if you touch it. So this resistor is probably over heating those 2 caps. But if you look is this pic:
You'll see I bent the resistor over to try and keep the heat away from the caps. This very small distance can in effect allow those caps to run 20 to 30 degree C cooler. And if you've been paying attention I dont have to explain what that means.
This also applies to other components.
As you can see in the above pic that transistor with the metal tab is usually an indication that is runs warm. And again is very close to a cap. But with a little bending:
Now another cap that is running cooler. So before you install that next board, take a good look at those caps and see if you can adjust anything to improve life.....
Enjoy....
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Nashou66
Joined: 12 Jan 2007
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