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Old 02-16-2008, 04:05 PM   #1
brockklich
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Default Confused cap values during removal- best fix?

I am attempting to repair a power supply for an LCD display. It failed to power on and there were 6 bulging caps that I feel confident are the problem.


4 of the 6 were in a row close together. I removed them all, without realizing that they were different values. Now I am not sure which values go into which place on the PCB. 2 were 470 uf / 25v and 2 were 1000 uf/ 10v. They all four appear identical, other than the markings.


I am trying to figure out my best plan. I cant find any info online about this particular PCB (TDK- model XAD819AR). I have no problem with experimenting with different combinations, but I dont know enough about how they work to know what to avoid. I understand I should never subsitute a lower voltage cap for a higher voltage one, but that the reverse is not true. How about the uf rating though? Could I safely install 1000uf 25 V caps in all four slots without (likely) destroying something else? Would the higher uf rating cause other problems either immediately or later on?

Is there another approach someone could suggest?

Thank you for any guidance.
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Old 02-16-2008, 04:39 PM   #2
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Default Re: Confused cap values during removal- best fix?

Quote:
1000uf 25 V caps in all four slots without (likely) destroying something else?
uhuh no probs

Quote:
Would the higher uf rating cause other problems either immediately or later on?
unlikely as long as they are the same spec. although its not technically a good idea in the long term to use 25v caps if there is only 5v in the circuit, prolly ok.

Quote:
Is there another approach someone could suggest?
yeah i would first look at the circles on the board, maybe the 25v are bigger. otherwise i would do the 1000uf 25 V recap then measure across the caps and figure out what is what. i am not sure about LCD voltages so cannot give some special advice.
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Old 02-16-2008, 10:13 PM   #3
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Default Re: Confused cap values during removal- best fix?

First of if you own a digital camera take a few happy snaps before pulling caps or anything, this can save your rear end.

Second "as the man said above "

Third if you like post some photos, sometimes someone will twig whats what from looking at it (top and bottom if you can, so people can see were the pcb traces go)

Seems mostly its will be the sm-psu or inverters that have these issues of popped caps
and a lot of the time thats the issue

Cheers
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Old 02-16-2008, 11:02 PM   #4
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Default Re: Confused cap values during removal- best fix?

The 1000 and 470 uf are probably secondary filters.

LCD monitor manufacurers like to use these values for the filters.

Upgrading them all to 1000uf will pose no problem.

Thats why I remove 1 cap at a time but sometimes I get impatient and remove them all but if I do I write down the component number and the value like this.

C11 1000uf 10V
C14 470uf 16V

You get the idea and as I install the caps I put checks next to the caps on the list. A picture is always a good idea too.

When recapping an Antec PSU I had to replace I cap soldered by the manufacurer where a resistor was mean't to be. I stupidly removed it without paying attention to the polarity.

The pics I took didn't show it. Luckily I traced the circuit out to acertain the polarity at the cap in question. I did this by tracing the traces which luckily ran to filter caps at each end. I was able to figure out the polarity and positioning but I wasted time by being careless.

Also when removing caps make sure that the silkscreen matches up because mistakes on the silkscreen can happen and you don't want to hear fireworks when you install your new caps .
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Old 02-17-2008, 01:30 AM   #5
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Default Re: Confused cap values during removal- best fix?

yeah on the screen printing (light and dark half circles)
there is some sort of standard but there is one MB that does it the other way so you can't trust them.

true too sometime they just don't help,
happy snaps photos but Id rather have some then none

Since mostly electrolytic's tend to be across rails of some kind you can sometimes work it out from that, what should be where too.
(not in all cases or circuits thought)

Cheers
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Old 02-17-2008, 10:53 AM   #6
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Default Re: Confused cap values during removal- best fix?

Thanks for all the great advice. I appreciate it.

I have studied the board closely and there are no printed markings that I can find that would indicated what goes where. However, the board is slightly darker on two of the location markers than on the other two. It looks as if these two had been at a higher temp than the other two. Would I expect either the 470 or the 1000 uf caps to run hotter? If so, I think I could confidently place them in the two darker openings.

There are marks as to what side is + / -

In the future, I will be sure to make a list of values and locations. In this case, I didnt do it because the 470s and the 1000s looked identical, and I presumed they were. I didnt realize until I had them all out to shop for replacements that they were different.

As far as replacements go, I was looking at Panasonic Bipolar Series SU series from Digikey (page 1481 on their current PDF catalog), but only because I dont know anything different. Should I consider another type?



Thanks.
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Old 02-17-2008, 12:38 PM   #7
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Default Re: Confused cap values during removal- best fix?

what series caps did you remove?
if these are secondary filters then you want something like panasonic FM
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Old 02-17-2008, 01:18 PM   #8
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Default Re: Confused cap values during removal- best fix?

the [email protected] will be fine if they fit.
some of these lcd's are a tight fit.
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Old 02-17-2008, 05:40 PM   #9
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Default Re: Confused cap values during removal- best fix?

Are you sure these are in the power supply and not the inverter section?
Inverters are frequency sensitive and uF may matter depending on what these caps are doing.
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Old 02-17-2008, 06:50 PM   #10
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Default Re: Confused cap values during removal- best fix?

Definitely it is on the power supply card.

Which is likely to have run hooter? the 25V 470 uf or the 10V 1000 uf?
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Old 02-17-2008, 07:34 PM   #11
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Default Re: Confused cap values during removal- best fix?

Um.. why don't you do what was already suggested? Put in the higher value caps, then check the voltage on each.

Once you find out what voltage is which cap, pull out the wrong ones, put in the right ones.
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Old 02-17-2008, 08:13 PM   #12
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Default Re: Confused cap values during removal- best fix?

Hooters run? - I'm in!!


If you can trace the circuit and find it's a PI filter the lower uF cap (470) probably goes on the power side of the coil and the higher 1000uF on the load side.

But like the others said.
If this is just an output filter it's not incredibly critical.
-
One thing though.
If this was 2 PI filters each with a 470 and a 1000 then you don't want to create one with two-470's and another with two-1000's.

.

You might try searching for the numbers on the PCB vs the screen's model number.

.
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Old 02-17-2008, 08:31 PM   #13
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Default Re: Confused cap values during removal- best fix?

Why would you need "Panasonic Bipolar Series SU series "

Don't take this the wrong way..as it does happen

My only suspicion is you don't know whats "positive" and "negative"
on the PCB...and yep that is very important to know or you will blow the caps if put in backwards

I have never seen a switcher using bipolars (of that value anyway)??
(could be wrong)


What are the original caps (brand series)?

An FM (or possibly preferably) FC would be more suitable for a switcher psu

Stand to be corrected on the below

On the heat Question
Thats not so easy to answer (I don't think) as it would really more depend on the amount of Ripple the cap was subjected too (and ESR)

Other factors such as ESR of cap ,can size would also factor into the equation.
(thats putting it simply)

There are 2 important things with caps for a switcher psu the ESR and Ripple of the Cap.

So knowing the brand and series would enable us to know whats best to use in there place

Mostly your safe going to a better speced device (such as FM FC) then what was there and usually although it might be supposedly a good cap
(specs wise) what was there, is crap.

So to give you an example
if you put say "General purpose" caps from say Rshite in ..yeah it might work and might even work for a few days, weeks
but much sooner rather then latter they will pop their tops and look just like what you had replaced.

So its "important" to use the "right cap for the job" or it will come back and bite you!

Your safest option is as above.... 1000 uf 25V in all then measure...
if you don't know

Also the capacitance range is nominal, a 1000 uf could be 1200uf or 800uf its a ball park figure (+- 20 percent from memory with electrolytics)

I have 1200uf ruby's that measure 1500 uf,

So using 1000 uf rather then 470 uf shouldn't be really a problem...granted it does as pcbonze has said depend on the circuit.
but in this case from those that posted above (and know there stuff) shouldn't be an issue.

HTH

Cheers
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Old 02-17-2008, 08:46 PM   #14
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Default Re: Confused cap values during removal- best fix?

Thanks Bonze
must have been posting at the same time.

(yeah from the sounds of it bonze there might be 2 circuits)

A photo of the PCB
would help..me at least anyway brockklich

willwakes fine post on how to do it HERE

Welcome too brockklich

were here to help, Cheers
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Old 02-17-2008, 08:58 PM   #15
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Default Re: Confused cap values during removal- best fix?

DEFINITELY DO NOT USE BIPOLAR. Replace with those recommended Panasonic FC or FM.
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Old 02-23-2008, 05:48 PM   #16
brockklich
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Default Re: Confused cap values during removal- best fix?

I went ahead and replaced the four with 1000Uf/25V Panasonic FMs from DigiKey. The total cost with shipping for these and a few others was about $13. The 1000s were a little larger than the 470s, but I got them in just fine and they work great. The display works like new. I just wanted to say thanks for all the great advice.
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Old 02-23-2008, 07:15 PM   #17
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Default Re: Confused cap values during removal- best fix?

Congrats!!
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Old 02-23-2008, 07:23 PM   #18
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Default Re: Confused cap values during removal- best fix?

Nice job!

Thats another perfectly good monitor saved from the landfill.
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Old 02-26-2008, 12:38 AM   #19
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Default Re: Confused cap values during removal- best fix?

Quote:
Originally Posted by brockklich
I am attempting to repair a power supply for an LCD display. It failed to power on and there were 6 bulging caps that I feel confident are the problem.


4 of the 6 were in a row close together. I removed them all, without realizing that they were different values. Now I am not sure which values go into which place on the PCB. 2 were 470 uf / 25v and 2 were 1000 uf/ 10v. They all four appear identical, other than the markings.


I am trying to figure out my best plan. I cant find any info online about this particular PCB (TDK- model XAD819AR). I have no problem with experimenting with different combinations, but I dont know enough about how they work to know what to avoid. I understand I should never subsitute a lower voltage cap for a higher voltage one, but that the reverse is not true. How about the uf rating though? Could I safely install 1000uf 25 V caps in all four slots without (likely) destroying something else? Would the higher uf rating cause other problems either immediately or later on?

Is there another approach someone could suggest?

Thank you for any guidance.
I have the same board with the exact same problem. If you are looking at the board from the TOP with the 4 Caps on the right side, and the smaller ones almost in the middle/right of the board. C56 and C54 are 1000 uf/ 10v, and C51 and C52 are 470 uf / 25v. Negative lead post to the edge of the board. The two smaller center ones (C101 and C102) are the same 220 uf / 25v.

Good Luck! let me know if it works for you, I've been looking for the same boad, but if the Caps needs to be replaced, I think I can do that myself.

CB
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Old 02-26-2008, 01:27 AM   #20
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Default Re: Confused cap values during removal- best fix?

seems you got it working brockklich good one

CB if the caps look "popped" or bulging then chances are thats you fix

something like this, either raised or with stuff coming out
(there I go using willawake's photo again )


post a pic if you like for opinions

welcome and Cheers
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