Author Topic: Questions over cap replacement  (Read 7123 times)

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Offline tyguy2

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Questions over cap replacement
« on: July 13, 2015, 08:13:09 pm »
I am helping a friend repair an older scope, and upon opening it, we found a cap that has been completely destroyed. The value says: 0.1 uf 1000 wv
Could I replace that with a 0.1 uf 1000v cap, or is there something I'm missing? If so, what would be a good replacement?
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Offline 4thDoctorWhoFan

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Re: Questions over cap replacement
« Reply #1 on: July 13, 2015, 08:24:30 pm »
I am helping a friend repair an older scope, and upon opening it, we found a cap that has been completely destroyed. The value says: 0.1 uf 1000 wv
Could I replace that with a 0.1 uf 1000v cap, or is there something I'm missing? If so, what would be a good replacement?

Yes, because the destroyed cap is a 0.1uf 1000V cap.  :P
The "wv" on the old cap means Working Volts.  It's just how they labeled things in the old days.
 

Offline tyguy2

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Re: Questions over cap replacement
« Reply #2 on: July 13, 2015, 08:28:29 pm »
So 1000v is fine?
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Offline 4thDoctorWhoFan

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Re: Questions over cap replacement
« Reply #3 on: July 13, 2015, 08:32:19 pm »
So 1000v is fine?
Yes, it's fine.  1000wv means the same as 1000V.
 

Offline tyguy2

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Re: Questions over cap replacement
« Reply #4 on: July 13, 2015, 09:00:44 pm »
I am helping a friend repair an older scope, and upon opening it, we found a cap that has been completely destroyed. The value says: 0.1 uf 1000 wv
Could I replace that with a 0.1 uf 1000v cap, or is there something I'm missing? If so, what would be a good replacement?

Yes, because the destroyed cap is a 0.1uf 1000V cap.  :P

This is the cap, looks blown to me   ;)
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Offline Excavatoree

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Re: Questions over cap replacement
« Reply #5 on: July 13, 2015, 09:03:09 pm »
I am helping a friend repair an older scope, and upon opening it, we found a cap that has been completely destroyed. The value says: 0.1 uf 1000 wv
Could I replace that with a 0.1 uf 1000v cap, or is there something I'm missing? If so, what would be a good replacement?

Yes, because the destroyed cap is a 0.1uf 1000V cap.  :P

This is the cap, looks blown to me   ;)

'Tis but a scratch.
 

Offline tautech

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Re: Questions over cap replacement
« Reply #6 on: July 13, 2015, 11:39:40 pm »
This is the cap, looks blown to me   ;)
Yep, it's buggered Jimmy.

Worry is finding a similar replacement.  :-//
I'd be looking for something like these:
http://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20150713153626&SearchText=104+1KV+capacitor

Others might like to advise too I hope.  :popcorn:
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Offline lowimpedance

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Re: Questions over cap replacement
« Reply #7 on: July 14, 2015, 01:54:51 am »
My bet something like this would be more than happy as a replacement.
http://au.element14.com/lcr-components/pc-hv-s-wf-100nf-1kv/cap-film-pp-100nf-1kv-axial/dp/9520341
Just check for physical dimensions to fit.
 Also fit some sleaving over the exposed leads before soldering in.
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Offline Shock

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Re: Questions over cap replacement
« Reply #8 on: July 14, 2015, 03:45:00 am »
The secret of cheap Japanese capacitors revealed... they stuff them with Kapton tape.
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Online Tomorokoshi

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Re: Questions over cap replacement
« Reply #9 on: July 15, 2015, 04:53:18 pm »
Replace the others at the same time.
 

Offline Mephitus

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Re: Questions over cap replacement
« Reply #10 on: July 15, 2015, 06:36:35 pm »
Related question: Is there be a particular performance characteristic of electrolytic caps that would cause you not to use something else such as a film, ceramic, mica, etc? I am having difficulty finding anything to study explaining the distinction on how to determine the best capacitor type for a given purpose.
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Offline vk6zgo

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Re: Questions over cap replacement
« Reply #11 on: July 16, 2015, 02:25:03 am »
I am helping a friend repair an older scope, and upon opening it, we found a cap that has been completely destroyed. The value says: 0.1 uf 1000 wv
Could I replace that with a 0.1 uf 1000v cap, or is there something I'm missing? If so, what would be a good replacement?

Yes, because the destroyed cap is a 0.1uf 1000V cap.  :P
The "wv" on the old cap means Working Volts.  It's just how they labeled things in the old days.

Or in Oz,the other way round,"vw"---they usually quoted both "volts working " & "volts peak",though!
 

Offline vk6zgo

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Re: Questions over cap replacement
« Reply #12 on: July 16, 2015, 02:30:07 am »
Related question: Is there be a particular performance characteristic of electrolytic caps that would cause you not to use something else such as a film, ceramic, mica, etc? I am having difficulty finding anything to study explaining the distinction on how to determine the best capacitor type for a given purpose.

The "Ginger Beers" will stroke their long beards & pontificate about this,but generally speaking,if a film cap or whatever has the same or better ratings,fit it.
In my opinion,circuits which rely upon the lousy characteristics of Electrolytic capacitors in order to work correctly are just poor designs.
 

Online mikerj

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Re: Questions over cap replacement
« Reply #13 on: July 16, 2015, 12:05:43 pm »
Related question: Is there be a particular performance characteristic of electrolytic caps that would cause you not to use something else such as a film, ceramic, mica, etc? I am having difficulty finding anything to study explaining the distinction on how to determine the best capacitor type for a given purpose.

They are primarily specified when you need a large amount of capacitance (e.g. 100's or 1000's of uF) since ceramic and film caps either aren't available in such high values, or would be enormous and expensive.

Many LDO regulators will oscillate if the output decoupling cap ESR is too low (e.g. a ceramic cap) so an electrolytic cap could be an option here.  However, electrolytics have enough disadvantages that a ceramic with a low value series resistor might be a more favourable option.
 

Offline AviatorLj

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Re: Questions over cap replacement
« Reply #14 on: August 03, 2015, 01:19:29 am »
Repaired it! It works almost perfect, but the waveform moves up slowly on the screen at certain v. atten. settings.
I reviewed it here and did a teardown: https://youtu.be/blirRLI_RxA
0:52 for talk and 5:00 for teardown
« Last Edit: August 03, 2015, 01:21:09 am by AviatorLj »
 


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