Replacing Hewlett Packard tantalums with...??? - Page 1
Forum section: electronics / repair

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 12, 2019, 02:49:08 pm
content: I recently picked up a HP 8160A Pulse Generator for cheap, and am looking through the beast to give it a once over and replace anything that looks suspect.So far I've found the usual leaky backup battery which I'll replace and repair, the expected compliment of Rifa mains filter caps that'll be swapped out, and also a tantalum cap that has disemboweled itself in the PSU. (See attached picture).I figure I'll replace all these caps on this board, if one has died, the rest might not be too far away... But I am wondering if there are any recommendations as to what to replace them with?Can I just stick some decent electrolytics in there? Looking at the prices of axial tantalum caps on Digikey, I think I'll be refinancing my mortgage to buy enough tantalum for this board.....The tantalums on this board have the following specs:180uF (+/-20%) 30V (One of which is blown)650uF (+/-20%) 20V

author: helius
author_rank: Super Contributor
timestamp: March 12, 2019, 04:17:29 pm
content: Lucky to catch that one before it corroded the board. Those look like Vishay 109D, non-hermetic wet tantalums. Because the seal is not hermetic, they can leak electrolyte, usually sulfuric acid.If you don't require extreme temperature capability you can probably use axial elcos like Nichicon TBE or Kemet PEG127. Tantalums were usually derated, so it may be okay to use a 25V replacement for a 30V part. 220uF also is an ok replacement for 180uF since these are not precise components (unless they were specially selected).

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 12, 2019, 05:03:29 pm
content: Nah, not specially selected, it's just bulk filtering on the power supply. Also got a 120mm fan right there, so temperature isn't an issue either.Probably wouldn't hurt to go a slightly higher capacitance either, seeing as it's PSU filtering.

author: SeanB
author_rank: Super Contributor
timestamp: March 12, 2019, 07:15:37 pm
content: Yes, pretty much any modern low ESR electrolytic will work there, next value up capacitance wise, and either same voltage or next up will work, they will pretty much fit in the place fine. Best is to go with radial ones and extend the one lead with insulated wire to match. Use a drop of gel superglue to attach them to the board after soldering and cleaning, and clean again after the glue has cured.

author: David Hess
author_rank: Super Contributor
timestamp: March 12, 2019, 10:41:37 pm
content: Like 4 times the capacitance is required when replacing a tantalum with an aluminum electrolytic to get the same high frequency performance but this is not difficult.Like SeanB suggests, I would get radial low ESR parts and bend one lead around.

author: bd139
author_rank: Super Contributor
timestamp: March 12, 2019, 10:45:44 pm
content: I tend to use a Vishay 2222 axial electrolytics for such jobs. Double capacitance. It usually works. If it doesn't, which has happened exactly once for me, the minor oscillation disappeared when I put a 1uF axial ceramic across it as well. (I use KEMET C440, only because I got a reel for nothing on ebay)

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 13, 2019, 03:01:24 am
content: Awesome, great info!I am slightly limited in space, so I'll have a look around to see what I can find to fit.For reference, here is the schematic of where these will be replaced (I'll probably replace all the caps on this board). Capacitor C224 is the bad one.

author: bd139
author_rank: Super Contributor
timestamp: March 13, 2019, 08:52:06 am
content: That’s a rather carefully designed supply that. I noticed TerraHertz did an ugly repair on one of these. So for reference:https://www.eevblog.com/forum/repair/show-us-your-ugly-repair/msg961484/#msg961484

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 13, 2019, 09:51:12 am
content: Ha, that there in that link is certainly a bodge...Well knowing I can go lower in voltage for the new caps is good. Means I can hopefully bump up the capacitance value at a lower voltage rating for an equivalent size package.I'll try to get axial caps if I can find suitable ones, just so it looks neat. I know you won't see it when it's reassembled, butI'll knowit's there.

author: bd139
author_rank: Super Contributor
timestamp: March 13, 2019, 09:59:18 am
content: I'm exactly the same with that one. I've got rid of kit because I know things like that are lurking inside it and can't face it being around

author: Tomorokoshi
author_rank: Super Contributor
timestamp: March 13, 2019, 05:01:26 pm
content: I'm trying to get a sample kit of Aluminum Polymer capacitors:https://www.digikey.com/products/en/capacitors/aluminum-polymer-capacitors/69Not a lot of high-frequency data on them, although it should be better than typical electrolytics.

author: GregDunn
author_rank: Frequent Contributor
timestamp: March 13, 2019, 06:31:51 pm
content: Related - what do people replace the cracked RIFA caps with? Are the new Kemet(Rifa) caps OK, or is there something better?

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 13, 2019, 06:33:43 pm
content: I use Kemet or Panasonic usually.Basically anything that isn't that nasty clear epoxy Rifa crap.

author: bd139
author_rank: Super Contributor
timestamp: March 13, 2019, 07:34:35 pm
content: Vishay and Epcos do nice cheap X2/Y2 caps as well.Kemet now sell RIFA btw

author: David Hess
author_rank: Super Contributor
timestamp: March 13, 2019, 11:48:38 pm
content: Quote from: Tomorokoshi on March 13, 2019, 05:01:26 pmThey are lower ESR so less capacitance can be used and like tantalums, high frequency performance is better. But the extremely low ESR can causes problems in some designs and they have a very limited voltage range.

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 14, 2019, 03:12:10 am
content: Quote from: bd139 on March 13, 2019, 07:34:35 pmYeah, I make sure to not buy the Rifa style caps from Kemet. I go for the plastic encased ones.

author: bd139
author_rank: Super Contributor
timestamp: March 14, 2019, 08:34:57 am
content: RIFA caps are fine to be honest. They’re sacrificial. I’ve seen the plastic ones explode too. Best option is assume that they have a ten year shelf life. Them and Schaffner filters!