Hameg HM1008, blowing rifa cap. - Page 1
Forum section: electronics / repair

author: Yamin
author_rank: Frequent Contributor
timestamp: June 27, 2022, 08:28:53 pm
content: Hi everyone,I had couple of HM1008 scopes repaired 5 years ago all with the input capacitor blown. Each unit started to fail one after the other (couple of months apart) giving out thick smoke *magic blue smoke. I replaced the rifa caps and the units have been working fine since.But I had the same problem occur couple of days back, and it was the first scope which became faulty and the first scope I replaced the cap. Now I'm afraid the rest of the scope are soon to follow.I know Rifa caps are notorious to blow up like this, but from what I have seen they should last for a long time. 5 years is too soon no?Any idea what could cause this? Could varying mains voltage cause this?Also noticed that the cap is very tightly packed with the heatsink touching it.Finally any suggestion on a suitable replacement which could be more reliable? When I replaced the caps I replaced them with the exact same one.Thanks in advance.

author: bd139
author_rank: Super Contributor
timestamp: June 27, 2022, 09:34:54 pm
content: Where did you buy the replacement RIFA caps from? They have a shelf life and can be compromised when not even powered up. Honestly I'd replace them with a different brand X2. Any one will do, just not another RIFA.And yes I've had a couple blow up on me

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: June 28, 2022, 11:08:48 am
content: Yes, there is a thread here somewhere where the new old stock RIFA already has cracks. These things have a shelf life.Never replace with RIFA with RIFA. I recommend the WIMA MKP-X2 series as a replacement.

author: Yamin
author_rank: Frequent Contributor
timestamp: June 28, 2022, 11:34:24 am
content: Actually I misspoke these were actually WIMA caps (I might have been thinking of another project).It was originally WIMA caps and I replaced them with the exact same type.Are WIMA caps known to blow up?Any suitable replacements for these?Thanks

author: bd139
author_rank: Super Contributor
timestamp: June 28, 2022, 12:41:23 pm
content: Never seen a WIMA blow up. That's new.Anything X2 rated, same voltage and capacitance and lead pitch will do the job.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 28, 2022, 01:14:12 pm
content: Never seen them smoke away either.They are also paper based so if they're NOS and the potting is compromised they'll suck up any dampness in the air and go off like RIFAs.Try a non-paper X2 model, they'll just fail silently by loosing capacity.

author: Yamin
author_rank: Frequent Contributor
timestamp: June 28, 2022, 05:20:37 pm
content: Interestingly I have come across some posts which has reported that these type of WIMA caps does smoke like RIFA caps. Something to do with the epoxy encapsulation having a poor expansivity characteristics.Which leads me to my next question. As there are different types of materials used for caps and the manufacturer has chosen a particular type should the replacement be of the same type? Or could it be of any kind?What could particular benefit of one type to the other?

author: bd139
author_rank: Super Contributor
timestamp: June 28, 2022, 05:22:34 pm
content: The only hard requirement is that it is X2 rated. I usually use the Epcos plastic ones.

author: BrokenYugo
author_rank: Super Contributor
timestamp: June 28, 2022, 07:23:59 pm
content: As mentioned by shakalnokturn, avoid paper dielectric caps like the plague. You'd think such junk wouldn't be allowed in a "safety" part, but it is.

author: bd139
author_rank: Super Contributor
timestamp: June 28, 2022, 07:29:51 pm
content: They’re fine but they have a shelf life. You just have to be aware of it.