Recapping - what's up with this large cap?? - Page 1
Forum section: electronics / general

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 23, 2019, 02:28:31 pm
content: I'm confused. Pulled this cap out of a CRT driver board. Needs recapping (has some nasty ass polyesters as well..). But.. what's up with the size of that thing??? 50V, 8.2uF?? Should be a fraction of the size. You could probably have a 8.2mF in that size. So, wha? Anyone knows?

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 23, 2019, 02:34:02 pm
content: Bipolar?

author: rsjsouza
author_rank: Super Contributor
timestamp: September 23, 2019, 03:33:28 pm
content: That or, depending on the age, higher voltage capacitors were quite sizeable.I had/have a few 35V and 50V capacitors from the 1970's and 1980's that had extreme sizes when compared to their contemporaneous counterparts. Although some of them survive to this day - I have a 75000µF/25V that is still kicking but is monstruous - about 15cm height x 6cm diameter.

author: Yansi
author_rank: Super Contributor
timestamp: September 23, 2019, 03:37:17 pm
content: BIPOLAR CAP! ... with rather high current capability. Part of the deflection resonant circuitry I guess.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 23, 2019, 03:40:35 pm
content: I was going to ask whether it was a polarized cap or not. So yeah you guys beat me to it.Yeah non-polarized electrolytics tend to be large, especially when this old.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 23, 2019, 04:45:42 pm
content: Ah! Hadn't considered that.Could this cap going bad account for the display not coming up at all?

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 23, 2019, 05:20:10 pm
content: A replacement has a diameter of 6.3mmStill feels like I'm missing something. I'll try to get more on it tomorrow.

author: SeanB
author_rank: Super Contributor
timestamp: September 23, 2019, 05:28:07 pm
content: That one being bad ( typically open circuit) generally results in the horizontal deflection being small, or to there being only a vertical line. Yes they need to handle a high current, as they pass the entire deflection current through them, so in general I replace them with 250V film units, though you do need to stack 2 or more on a set of stiff wire leads to get the right capacitance, as the more common bipolar capacitors are more meant for use as louspeaker crossovers, and are pretty poor for ESR, current capability and long life with bias applied. 250V film as that is generally available in 4.7uF and 2.2uF and not too large, and the capacitor has a bigger connection to the foil so lowering the ESR.With a CRT monitor be suspicious of any resistors in the higher voltage rails, pretty much check ( in circuit or out, though you get a better reading out of circuit) all resistors that are over around 10k that they have not gone either high in value or open circuit. Remember as well that replacement resistors must be of adequate power rating and appropriate voltage rating, you might end up putting in 1W resistors for the voltage rating, despite the resistor being only dissipating 0.2W in circuit, but it is a 2M2 resistor and has 800V across it.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 23, 2019, 05:49:22 pm
content: No line at all. Will have to look further, then..

author: Yansi
author_rank: Super Contributor
timestamp: September 23, 2019, 06:08:26 pm
content: Quote from: SeanB on September 23, 2019, 05:28:07 pmlol, loudspeaker crossover caps shall indeed handle quite some current, don't you mean those silly 5x11 package style radial ones, clearly meant for signal circuits?

author: ebastler
author_rank: Super Contributor
timestamp: September 23, 2019, 08:18:42 pm
content: Quote from: Ice-Tea on September 23, 2019, 02:28:31 pmI'll take your word for it, since I can't read a thing on that photo.Could you take a better picture without the light reflections? Any manufacturer name or type designation on that cap?

author: vk6zgo
author_rank: Super Contributor
timestamp: September 24, 2019, 09:11:21 am
content: Quote from: Ice-Tea on September 23, 2019, 05:20:10 pmDon't be surprised if the replacement cap releases the magic smoke!I had a similar one in the boost HT circuit of an Electrohome monitor, where the replacement cap did that.It seems those caps are special in two ways:-they are bipolar&they are "high ripple current" (low ESR) types.I replaced it with a "Christmas tree" of polyester greencaps.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 24, 2019, 11:43:42 am
content: Hmm.. these seem to be close. Including ridiculous size & current rating.http://www.mouser.com/ds/2/293/e-ha-5630.pdf

author: SeanB
author_rank: Super Contributor
timestamp: September 24, 2019, 12:05:24 pm
content: Quote from: Yansi on September 23, 2019, 06:08:26 pmYes, but loudspeaker caps are only going to have intermittent high power applied, in general having an ESR in the ohms range is not a worry, but for line scan you run at around 10A average current in the capacitor all the time the set is powered.