Questions over cap replacement - Page 1
Forum section: electronics / repair

author: tyguy2
author_rank: Unknown
timestamp: July 13, 2015, 08:13:09 pm
content: 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 wvCould 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?

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: July 13, 2015, 08:24:30 pm
content: Quote from: tyguy2 on July 13, 2015, 08:13:09 pmYes, because the destroyed cap is a 0.1uf 1000V cap.The "wv" on the old cap means Working Volts. It's just how they labeled things in the old days.

author: tyguy2
author_rank: Unknown
timestamp: July 13, 2015, 08:28:29 pm
content: So 1000v is fine?

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: July 13, 2015, 08:32:19 pm
content: Quote from: tyguy2 on July 13, 2015, 08:28:29 pmYes, it's fine. 1000wv means the same as 1000V.

author: tyguy2
author_rank: Unknown
timestamp: July 13, 2015, 09:00:44 pm
content: Quote from: 4thDoctorWhoFan on July 13, 2015, 08:24:30 pmThis is the cap, looks blown to me

author: Excavatoree
author_rank: Frequent Contributor
timestamp: July 13, 2015, 09:03:09 pm
content: Quote from: tyguy2 on July 13, 2015, 09:00:44 pm'Tis but a scratch.

author: tautech
author_rank: Super Contributor
timestamp: July 13, 2015, 11:39:40 pm
content: Quote from: tyguy2 on July 13, 2015, 09:00:44 pmYep, 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+capacitorOthers might like to advise too I hope.

author: lowimpedance
author_rank: Super Contributor
timestamp: July 14, 2015, 01:54:51 am
content: 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/9520341Just check for physical dimensions to fit.Also fit some sleaving over the exposed leads before soldering in.

author: Shock
author_rank: Super Contributor
timestamp: July 14, 2015, 03:45:00 am
content: The secret of cheap Japanese capacitors revealed... they stuff them with Kapton tape.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: July 15, 2015, 04:53:18 pm
content: Replace the others at the same time.

author: Mephitus
author_rank: Regular Contributor
timestamp: July 15, 2015, 06:36:35 pm
content: 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.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 16, 2015, 02:25:03 am
content: Quote from: 4thDoctorWhoFan on July 13, 2015, 08:24:30 pmOr in Oz,the other way round,"vw"---they usually quoted both "volts working " & "volts peak",though!

author: vk6zgo
author_rank: Super Contributor
timestamp: July 16, 2015, 02:30:07 am
content: Quote from: Mephitus on July 15, 2015, 06:36:35 pmThe "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.

author: mikerj
author_rank: Super Contributor
timestamp: July 16, 2015, 12:05:43 pm
content: Quote from: Mephitus on July 15, 2015, 06:36:35 pmThey 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.

author: AviatorLj
author_rank: Contributor
timestamp: August 03, 2015, 01:19:29 am
content: 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_RxA0:52 for talk and 5:00 for teardown