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Old 05-11-2009, 04:03 PM   #1
ceramic
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Question Replacing capacitors

When replacing a capacitor, does the capacitance have to be strictly the same? I know the voltage doesn't necessarily have to be the same but the new one has to be higher than the one you are replacing. So for instance, can you replace a 680uF 10V capacitor with an 820uF 25V capacitor (in case that's the only one you have handy and don't have time to order the same rating as the original). Thanks.
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Old 05-11-2009, 04:22 PM   #2
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Default Re: Replacing capacitors

It depends on what you are working on.
If cap is part of a tuned circuit then uF may be critical.
For filter caps on mobo's not so much.
As long as you don't lower ESR too.....
Going up a bit is okay [and may be an upgrade].
Going down 20% should be okay but definitely don't lower ESR too when going down.
-
Most mobo caps are +/-20% on the uF spec anyway so one size down is usually still in the 20%.
uF tends to go down as they age so new cap at lower uF will be like old cap as aged.
Only concern going down like that is new lower uF cap's uF goes too low as it ages.
Even that -usually- isn't a problem because -usually- mobos design tolerance is wider than caps rating tolerance.
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Old 05-11-2009, 04:24 PM   #3
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Default Re: Replacing capacitors

i would say it depends where it is.
if it's output cap, then such increase probably won't hurt.

if it's cap that is a passive component for some ic, i would stick with exact value.
but given it's pretty high value, it's probably output, so you should be fine.

if in doubt, post pics and i'll tell you is it output cap or otherwise...
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Old 05-11-2009, 04:30 PM   #4
ceramic
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Default Re: Replacing capacitors

Quote:
Originally Posted by PCBONEZ
It depends on what you are working on.
If cap is part of a tuned circuit then uF may be critical.
For filter caps on mobo's not so much.
As long as you don't lower ESR too.....
Going up a bit is okay [and may be an upgrade].
Going down 20% should be okay but definitely don't lower ESR too when going down.
-
Most mobo caps are +/-20% on the uF spec anyway so one size down is usually still in the 20%.
uF tends to go down as they age so new cap at lower uF will be like old cap as aged.
Only concern going down like that is new lower uF cap's uF goes too low as it ages.
Even that -usually- isn't a problem because -usually- mobos design tolerance is wider than caps rating tolerance.
What if you are working a power supply for a DVD player?
Also, is there a way of finding the ESR value without buying those expensive ESR meters.
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Old 05-11-2009, 04:34 PM   #5
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Default Re: Replacing capacitors

for dvd player power supply: on primary try to be as close as possible, on secondary it's passable to do increase you mention.

>Also, is there a way of finding the ESR value without buying those expensive ESR meters.

not unless you make one...
for example
http://www.badcaps.net/forum/showthr...hlight=manfred

but i wouldn't say anatek blue esr is awfully expensive as a kit..
http://www.anatekcorp.com/blueesr.htm

then again it's not very cheap either.


but for one dvd player repair you don't need esr meter, really...just follow what i said above.
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Old 05-11-2009, 04:50 PM   #6
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Default Re: Replacing capacitors

Quote:
Originally Posted by i4004
for dvd player power supply: on primary try to be as close as possible, on secondary it's passable to do increase you mention.

>Also, is there a way of finding the ESR value without buying those expensive ESR meters.

not unless you make one...
for example
http://www.badcaps.net/forum/showthr...hlight=manfred

but i wouldn't say anatek blue esr is awfully expensive as a kit..
http://www.anatekcorp.com/blueesr.htm

then again it's not very cheap either.


but for one dvd player repair you don't need esr meter, really...just follow what i said above.

I believe its the secondary side. Couldnt attach pic cos its too large but i'm sure i'm right so no need.
Thank you so much.

Last edited by ceramic; 05-11-2009 at 04:55 PM..
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Old 05-11-2009, 04:58 PM   #7
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Default Re: Replacing capacitors

Quote:
Originally Posted by ceramic
What if you are working a power supply for a DVD player?
Tuned circuits usually are used in signal processing.
Not likely to have such an issue in a power supply section of anything.

Quote:
Originally Posted by ceramic
Also, is there a way of finding the ESR value without buying those expensive ESR meters.
Without a meter the best way is to find the data sheet for the old caps.
Not always possible but often is.

What are they?





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Old 05-11-2009, 05:08 PM   #8
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Default Re: Replacing capacitors

>Not likely to have such an issue in a power supply section of anything.

well in psu you can have just slightly changed capacitance(not even esr) on primary side cap blowing the stabiliser(for b+ flyback supply) of a pc monitor...

>I believe its the secondary side.

yes, those usually go on dvd-players...and vcrs, etc.
feel free to change those as intended.
if still in doubt, primary is usually marked "hot" and has some sort of marking(drawn lines on the soldering or component side) to distingush it from secondary...

be carefull with polarity, minus marking on cap should match those of previous cap.
reversing it could lead to some smoke and simillar pyrotechnics...

Last edited by i4004; 05-11-2009 at 05:10 PM..
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Old 05-11-2009, 05:17 PM   #9
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Default Re: Replacing capacitors

Quote:
Originally Posted by i4004
>Not likely to have such an issue in a power supply section of anything.

well in psu you can have just slightly changed capacitance(not even esr) on primary side cap blowing the stabiliser(for b+ flyback supply) of a pc monitor...

>I believe its the secondary side.

yes, those usually go on dvd-players...and vcrs, etc.
feel free to change those as intended.
if still in doubt, primary is usually marked "hot" and has some sort of marking(drawn lines on the soldering or component side) to distingush it from secondary...

be carefull with polarity, minus marking on cap should match those of previous cap.
reversing it could lead to some smoke and simillar pyrotechnics...

thanks for the tip and warning. yeah I have fried a few circuits by not considering the polarity. I've learnt that lesson now for good .
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Old 05-11-2009, 06:11 PM   #10
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Default Re: Replacing capacitors

finally got it working....no problems so far. hope it stays that way
Thanks for all your help!
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