A question on CRT monitor capacitors - Page 1
Forum section: electronics / repair

author: uneksija
author_rank: Newbie
timestamp: January 13, 2018, 12:11:55 pm
content: Hi, first post...I'm repairing a Commodore 1084S-D CRT monitor. I'm quite sure I've located the problem - one of the about 40 electrolytic capacitors needs replacing. Now I'm trying to figure which kind of electrolytic cap to use. Attached is a snip of the parts list of the service manual of the monitor. The cap in question is C306. It’s described in the parts list as ”C ELECTRO 25V 47uF RS”. Now I'm wondering what that "RS" means? And in general, what those letters at the end of the part description mean (please see the attached picture)? Electrolytic caps have "RS", "RU" etc., mylar caps have "J" and "J (ED)" etc - what do they mean?Would any basic 47 uF 25V electrolytic cap do the trick, or is there something else I should take into account than just capacitance and voltage rating?Thanks in advance!

author: wraper
author_rank: Unknown
timestamp: January 13, 2018, 12:23:50 pm
content: Dunno what RS means but you can use any 47uF electrolytic cap with at least 25V voltage rating. And if you are particularly eager to know more about the capacitor, you should attach a photo of the capacitor itself, so brand and series are known. In any case that's just some general purpose capacitor.

author: wraper
author_rank: Unknown
timestamp: January 13, 2018, 12:32:20 pm
content: "J" likely means 5% tolerance. I don't think that "RS" is something standard, likely just shortened description , like "reduced size" or something else.

author: mariush
author_rank: Super Contributor
timestamp: January 13, 2018, 12:40:24 pm
content: They're probably some average general purpose capacitors.RS and RU i don't know if they're some specific code or a capacitor series. If it's a capacitor series, if you're lucky they're Nichicon RS series and RU series, for which i've attached the datasheets below.You should be able to replace them with some of the higher end standard capacitors or some of low esr electrolytic capacitors (but not those super low esr capacitors meant for switching power supplies)Here's some charts :https://www.badcaps.net/forum/showthread.php?t=66757- look for those series at the top of "standard capacitors" and the ones that go towards "low impedance"For example, I'd probably use Panasonic FC or FK , Rubycon PX (standard 105c) or YXF or ZL (105c, lower esr) , Nichicon VZ (standard 105c) or PS or PW (lower ESR) , United Chemi Con / Nippon Chemi Con KME (105c standard) or LXY or KY (lower esr)

author: wraper
author_rank: Unknown
timestamp: January 13, 2018, 02:35:29 pm
content: There is absolutely no need to use LOW ESR series, it actually could do more harm than good as this circuit is designed with general purpose capacitors to begin with. And I doubt that would add any reliability, as there is no high ripple current and LOW ESR types often last less than general purpose types if used in conditions with no stress.

author: mariush
author_rank: Super Contributor
timestamp: January 13, 2018, 02:41:55 pm
content: You're correct - note that I recommended only some which are barely "low esr" because often they'll also have better electrolytic solutions or better lifetime ratings.Some won't even consider capacitors like Panasonic FC series low esr anymore.I wouldn't suggest using the same capacitors you'd use on motherboards or computer power supplies, way too different specification wise to be sure they'll work right.

author: wraper
author_rank: Unknown
timestamp: January 13, 2018, 02:51:10 pm
content: Quote from: mariush on January 13, 2018, 02:41:55 pmThere are compromises. If capacitor is optimized for LOW ESR, it actually may reduce electrolyte long term stability as such as a compromise. Therefore if I would aim for highest reliability in no stress conditions, I would aim for general purpose capacitors with highest life spec.

author: floobydust
author_rank: Super Contributor
timestamp: January 14, 2018, 05:56:04 am
content: For this size (47uF) I am careful to note the ripple current rating, as it varies widely between capacitor lines.It seems to be why they have a short life, in some applications.

author: Specmaster
author_rank: Super Contributor
timestamp: January 14, 2018, 09:21:11 am
content: Quote from: uneksija on January 13, 2018, 12:11:55 pmCould it be that RS means Radial Series as opposed to Axial Type?

author: Rasz
author_rank: Super Contributor
timestamp: January 14, 2018, 08:40:42 pm
content: Quote from: uneksija on January 13, 2018, 12:11:55 pm~30 year old crt, most likely all need replacing

author: uneksija
author_rank: Newbie
timestamp: February 03, 2018, 08:17:23 pm
content: Thanks for the information!I finally desoldered the capacitor to examine it more closely. Attached are two photos of the capacitor in question. It seems to be 35 volts, not 25 like in the service manual of the monitor. The capacitor is made by Daewoo and has the label "RS" on it ("RS" is also what was in the service manual). So does this mean it's "RS series"? Other markings are (visible in the other picture) +- 20%, 85 degrees C and something which is probably "8S".Based on the above information, is there anything I should take into account when ordering a replacement part, or will any decent general purpose 47uF 35 volt capacitor do?

author: floobydust
author_rank: Super Contributor
timestamp: February 04, 2018, 12:25:46 am
content: "RS" denotes the series of Daewoo electrolytic capacitor. I don't see datasheets for it, vintage Korean parts. Newer "RSS" series is a vanilla part.Same C306 also failedCommodore 1084S-P1 repair log (part 3)It is part of the vertical-deflection yoke feedback circuit. ESR is not criticalbut I would say ripple-current rating is, for long life.Most 47uF electrolytic caps are rated about 100-150mA ripple.Nichicon has UPX series rated 315mA, Rubycon ZLJ 225mA.A 35V part can take a bit more ripple current than a 25V part.If you can get a high ripple rated part, great. A vanilla part will workbut shorter life.If C307 is getting old, it could add stress to C306. So I would check C307.Edit: the cap circuit has a lot of series resistance so it should not be subjected to high ripple currents.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 04, 2018, 12:39:01 am
content: Use a 105C as a replacement, since CRTs are known for getting quite warm.

author: Bashstreet
author_rank: Frequent Contributor
timestamp: February 04, 2018, 02:59:07 pm
content: Quote from: uneksija on February 03, 2018, 08:17:23 pmPretty much any good quality 35v 47uf electrolytic will do . Best choose 105 degree model with similar if not same dimensions (do not buy tiny ones as you might end with heat dissipation issues)Just make sure you get the polarity right.

author: andy2000
author_rank: Frequent Contributor
timestamp: February 04, 2018, 04:23:44 pm
content: You're way overthinking it. Any modern name brand cap will be much better than the originals that lasted 30 years. Personally, Nichicon PW is my go to general purpose cap, but you'd have a hard time finding ones that don't work well in this.

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2018, 12:22:32 am
content: I was going to say almost exactly what Andy posted. Don't get caught up worrying about the little details, just get some good quality general purpose replacements. Personally I like Nichicon, Rubycon and Panasonic capacitors but there are other good ones. I normally select long life types rated for 5,000 hours or more when available and when physical size allows.