Tektronix NOS Caps Reforming - Page 1
Forum section: electronics / repair

author: Stonie
author_rank: Newbie
timestamp: February 05, 2024, 01:11:35 am
content: Hi All,As part of my ongoing restoration of a newly aquired Tektronix 2465A scope, I took delivery over the weekend of a new pair of the large axial PSU caps @ 300uf 250v.The supplier informed me, they took delivery of these caps a couple of years ago.Although I haven't checked the date code yet, my question is; are these caps considered NOS and will they require reforming before use ?Any advice welcome...TIA, Phil.

author: wraper
author_rank: Unknown
timestamp: February 05, 2024, 01:14:49 am
content: Unless they are 15+ years old, it's absolutely unnecessary.

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2024, 02:11:34 am
content: I don't like that practice because I took some caps apart and while they worked it was pretty brown in some spots in there. I took others apart and it was white. I don't like brown color near/in electronics things. The sprague looks like if you left a roll of toilet paper in a dish of water and then stuffed it into a tube. When stuff is browning it makes me feel that its probobly not in great condition. It looks like chemical damage and I don't think you will restore it with anything electronic.

author: wraper
author_rank: Unknown
timestamp: February 05, 2024, 02:40:01 am
content: Why would capacitor need to be white inside? It's not like paper used in capacitors is bleached like office paper

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2024, 02:45:36 am
content: because it was turning brown. Parts of it looked white. I took 8 apart. 2 were brown and 6 were nice and white. They are infact quite white when in good condition. ESR test was OK.I believe that is a sign of acid damage, when old paper turns color. It could be anything between improperly processed paper or whatever that stuff is, or some kind of reaction with electrolyte (possibly lightly contaminated).

author: wraper
author_rank: Unknown
timestamp: February 05, 2024, 11:14:33 am
content: Quote from: coppercone2 on February 05, 2024, 02:45:36 amIME they usually become light color instead of brown when electrolyte dries up.

author: DavidAlfa
author_rank: Super Contributor
timestamp: February 05, 2024, 11:44:51 am
content: Better replace them, they tend to leak or develop high ESR, I've recapped a dozen of 2245 / 2465A/B.Edit: The low voltage ones. I found zero bad HV caps.Ooops, missed they were new:Quote from: Stonie on February 05, 2024, 01:11:35 am

author: tggzzz
author_rank: Super Contributor
timestamp: February 05, 2024, 12:21:50 pm
content: Quote from: Stonie on February 05, 2024, 01:11:35 amIn general reforming capacitors is atemporary"fix" for a terminally ill capacitor, useful principally to see whether there areotherproblems in the equipment.What makes you sure those existing capactors need to be replaced? The LV electrolytics yes, as perhttp://www.condoraudio.com/wp-content/uploads/Projects/Tektronix-2465B-Oscilloscope-Restoration-Repair.pdfDon't fiddle with U800 unless necessary: the original mechanical design is poor, and fiddling oftencausesproblems.

author: wraper
author_rank: Unknown
timestamp: February 05, 2024, 12:56:39 pm
content: Quote from: tggzzz on February 05, 2024, 12:21:50 pmHe asked about reforming brand new capacitors.

author: tggzzz
author_rank: Super Contributor
timestamp: February 05, 2024, 02:30:12 pm
content: Quote from: wraper on February 05, 2024, 12:56:39 pmCorrect.The OP explicitly states that they are several years old, and he has not looked at the datestamp. Hence they are not "brand new".Personally I doubt reforming will be relevant, but only the OP has sufficient information to determine that.

author: jonpaul
author_rank: Super Contributor
timestamp: February 05, 2024, 03:34:46 pm
content: recapping can lead to more issues.if it anit broke dont fix.Exception is bad bulk PSU lytics on miand bus and Rifa VDE X, Y EMI filter caps.See many posts on groups.io Tekscopes and Tekscopes 2 alsoQservice in Greece and Condor Audio in Isreal on recapping and serive of 246X/A/B.Get exact sefv many for the model and SNJ