Bloody RIFA caps again - Page 1
Forum section: electronics / repair

author: BradC
author_rank: Super Contributor
timestamp: August 21, 2023, 10:05:46 am
content: Due to "circumstances" I haven't had the opportunity to use my lathe since about 2018. Of course when I went to use it yesterday the VFD was randomly tripping the RCD. The RCD is right above the lathe so I put up with it for a while, then decided it was time to pop the lid off the VFD. I snuck a look under the logic card to the power board to see 4 RIFA caps smiling back at me.Today I popped the logic board off and saw them in their full glory. I put a meter in series with the earth line and saw it started at about 2mA leakage, and gradualy climbed to ~10mA when I gave up. I decided as they were Y caps and supposed to "safely fail open", I'd cheat a little bit. As Big Clive would say "naughty". So I clipped the earth pin on the VFD to the Neutral through the milliameter and came inside to wait. The VFD sits in my Granny Flat at the back of the yard. About 15 minutes later I heard a loud "pop" and thought, that'll be it.I was greeted with the culprit in its full glory, opened like a kernel of popcorn. Probably not the most kosher way of identifying the faulty device, but did the job. Of course it's going to take some time to get the smell out of the place.Of course the pads are under the IGBT pack, so that had to come out. Lots of use of the desoldering gun and half a roll of wick later (and a bit of swearing) and it's ready for a Digikey order and some new caps.

author: Haenk
author_rank: Super Contributor
timestamp: August 21, 2023, 01:47:17 pm
content: no point in testing them at all, replace on sight

author: BradC
author_rank: Super Contributor
timestamp: August 21, 2023, 03:35:12 pm
content: Quote from: Haenk on August 21, 2023, 01:47:17 pmYes and no. I was pretty sure they were the culprits, but before committing an hour to removing the IGBT block I really wanted to be doubly sure. I was also interested as to which one of the 4 was the real problem, so I just used the sledgehammer approach to see what went pop. It certainly went pop.The IGBT block has 15 pins that are a friction fit in the holes, so getting them to a point I could remove without damaging the board or block was a slow and careful process. I don't think it was built to be repaired, but it's a typical early 90's German construction where everything is engineered to last so I'm hoping replacing these caps will see it outlast me. Unlike the disposable Chinese inverters commonly used today.

author: Haenk
author_rank: Super Contributor
timestamp: August 21, 2023, 09:27:18 pm
content: Judging from the pictures, the rightmost RIFA looks like it already had a massive crack in the beginning. So immediate action was necessary anyway. Considering the massive explosion that might have happened and the risk of damaging stuff, I would not have turned it on

author: BradC
author_rank: Super Contributor
timestamp: August 21, 2023, 11:56:42 pm
content: Quote from: Haenk on August 21, 2023, 09:27:18 pmYeah, I thought it was probably the right one also. 4 Caps. One on the input and one on each output phase, so the output caps had nothing across them and one of those was the one with the almighty crack. Hindsight I shouldn't have tossed them out, but put a danger lead on them all and videoed them going up in smoke.I've had enough RIFA caps go on me I know they make a mess, but I can't see any "massive explosion". At best they smoke, they usually puke and rarely they either spark or flame a bit. Where they are on the board there's pretty much no chance of collateral damage and doing it this way gives "positive confirmation". I have a spare "Chinese" inverter handy, I just wanted to confirm it was going to be an easy fix before committing to getting that IGBT block out.

author: ArdWar
author_rank: Frequent Contributor
timestamp: August 22, 2023, 06:37:07 am
content: The problem with doing "fault finding" that way is that old (and damp) PCB often have unknown trace adhesion strength left on them. Depends on the failure mode (and in this case which side gave way first) they sometimes lift the trace with them, if not outright blasting it leaving a char.

author: Shonky
author_rank: Frequent Contributor
timestamp: August 22, 2023, 08:52:41 am
content: Yeah I don't really understand the concept of bypassing a protection device and waiting for a specific type of component to blow up when it's well documented that these components notoriously fail, also risking further collateral damage in the process.

author: BradC
author_rank: Super Contributor
timestamp: August 22, 2023, 12:54:59 pm
content: <shrug> Where's your sense of adventure?

author: Psi
author_rank: Super Contributor
timestamp: August 22, 2023, 01:00:51 pm
content: "Look, I don't wanna mess with no RIFA addicts, okay"

author: madires
author_rank: Super Contributor
timestamp: August 22, 2023, 01:06:54 pm
content: Isn't RIFA the acronym for 'Replace Immediately, Fire Ahead'?

author: Swake
author_rank: Frequent Contributor
timestamp: August 24, 2023, 02:38:32 pm
content: Rifa merits a class action lawsuit for these.

author: Haenk
author_rank: Super Contributor
timestamp: August 24, 2023, 02:44:57 pm
content: Quote from: Swake on August 24, 2023, 02:38:32 pmWell, they *did* work for at least 2 decades. Also, filter caps could be considered consumables which require regular checks and replacement.But yes, they are a PITA and found everywhere.

author: BradC
author_rank: Super Contributor
timestamp: August 24, 2023, 03:08:09 pm
content: Quote from: Haenk on August 24, 2023, 02:44:57 pmI rate X and Y caps a bit the same as MOVs. They're self healing for a reason, and as such consumable. On the other hand, the difference between a gradual degradation or thermonuclear stink bomb is pretty significant.I figure another couple of RIFA explosions and I'll have come up with an effective chemical cocktail as a stench remover. Thus far I haven't succeeded (Chloroform did bad things to the plastics!). I do have 2 devices left with RIFA's, but I love my HP 3478a's and I have a little box full of replacements to use before I power them on. I might save the removed caps to torture later.

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 24, 2023, 11:59:50 pm
content: Quote from: BradC on August 21, 2023, 03:35:12 pmFunny... The silkscreening on that PCB looks so Japanese to me.Which German name is on the box? Who's is on the IPM Mitsubishi or Fuji Electric?

author: rsjsouza
author_rank: Super Contributor
timestamp: August 25, 2023, 02:49:16 am
content: If Rifa had to get a class action suit by working only a couple of decades, then the entire capacitor industry and its electrolytic parts would go down with it.Things have a lifespan and only somewhat recently (in industry terms) failsafes were started to be used for these parts.

author: BradC
author_rank: Super Contributor
timestamp: August 25, 2023, 06:31:22 am
content: Quote from: shakalnokturn on August 24, 2023, 11:59:50 pmIt's a NORDACcompactmade by Schlicht + Kuchenmeister GmbH & Co with a 1993/94 serial number. (the u has an umlaut but I'm not clever enough to put it in). The IGBT block is made by Siemens.Anyway, new caps fitted and re-assembled. It'll probably go another 30 years given the intermittent use I give it. The Lathe it drives is a 1954(ish), so they'll both probably outlive me.