Obvious PSU fault - Page 1
Forum section: electronics / repair

author: 1980s_john
author_rank: Contributor
timestamp: May 10, 2017, 09:49:17 pm
content: Hi,I went to a remote site today and found this PSU - no prizes for spotting the failed cap! I had to scrape out the remains from the chassis.I haven't seen one fail quite so spectacularly, luckily there was a spare PSU on site I could swap in. I don't think I will repair this one, but maybe time to check the spare working PSUs and re-cap one ready for next time.Regards,John

author: tautech
author_rank: Super Contributor
timestamp: May 10, 2017, 09:59:24 pm
content: IMHOallthose e caps are past their best before date.

author: floobydust
author_rank: Super Contributor
timestamp: May 10, 2017, 10:07:52 pm
content: I see a lot of 1984 date codes, hmmm over 30 years old that's pretty good life. The cap died of old age or maybe a transient or semi failure, it's only rated for 10V.Those blue Philips electrolytics are horrible, I hate them they had poor lifetimes and fail short or openAxial parts are obsolete hard to get. If the customer still wants to run old gear like this, I'd recap the boards.

author: MagicSmoker
author_rank: Super Contributor
timestamp: May 10, 2017, 10:25:48 pm
content: Rifa made top-notch capacitors back in the day, but that day was, indeed, 30+ years ago. Axial elkos are getting harder to find, but there should still be sufficient stock at the usual legit distributors like Farnell, RS, Digikey, etc.Not sure of your skill/experience level with electronics, but usually the value of elkos isn't too critical, so it would be perfectly reasonable to replace all capacitors of, say, 470uF to 1000uF (aka 1mF) with 1000uF units. In other words, don't go searching too hard for that 680uF/16V capacitor...

author: james_s
author_rank: Super Contributor
timestamp: May 11, 2017, 01:01:40 am
content: It's pretty easy to replace axial caps with radial if necessary. It can even be done fairly tidy if one is careful, splice on a longer lead, slip some heatshrink over it and fold it back against the body of the cap. A small zip tie on the far end provides mechanical support.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 11, 2017, 06:19:06 am
content: I wonder what kind of functionality they squeezed out of that discrete control circuit. I don't see a current shunt resistor. It may simply be self resonant. In which case it probably gets quite hot if there's an accidentally shorted output. Who knows.Tim

author: Wirehead
author_rank: Regular Contributor
timestamp: May 11, 2017, 07:52:52 am
content: Seems it's always the rifa's that exlode... Same thing with their X2 caps.. Smokin' formula

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: May 11, 2017, 08:28:01 am
content: Well at least it failed open.....For a moment there I was sure that writing on the side read 'AILING POWER CARD', but I guess that was my imagination. I guess if those RIFA caps are getting to a point where they are failing spectacularly like that due to ageing, it would seem sensible to do some pro-active maintenance and replace them.

author: DTJ
author_rank: Super Contributor
timestamp: May 11, 2017, 08:37:15 am
content: Quote from: WaveyDipole on May 11, 2017, 08:28:01 amI got a laugh out of that too.Out of interest what is the PSU out of?It reminds me of mid 80's telecomms line terminal gear.

author: cvanc
author_rank: Frequent Contributor
timestamp: May 11, 2017, 12:46:20 pm
content: Quote from: floobydust on May 10, 2017, 10:07:52 pmI totally agree. The old blue Philips electrolytics that say MADE IN HOLLAND are trouble, especially in warm environments.

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: May 11, 2017, 02:42:32 pm
content: Curious since I have been led to believe that those Philips blue caps are actually very stable, although admittedly 'warm environments' (unlike the UK for most part) might make a difference. I would expect those on board transistors put out quite a bit of heat so 30 years of service doesn't seem too bad a lifespan.....I recently replaced a couple of axial caps in an oscilloscope with equivalents from Vishay. There did seem to be less manufacturer options as well as capacitance values available but some can still be found. Unfortunately they do tend to cost a premium in comparison to an identically rated radial.

author: floobydust
author_rank: Super Contributor
timestamp: May 12, 2017, 01:44:31 am
content: The blue Philips electrolytics, anytime I encounter one, it has failed. The rubber bung cracks; hopefully they've dried out- but many short. Replaced hundreds on Neve recording consoles.This PSU is a weird design- all those high power semi's (TO-3, stud mount diodes) with no heatsinking. When is a 20A diode not a 20A diode? After a second...

author: GreyWoolfe
author_rank: Unknown
timestamp: May 12, 2017, 11:56:17 am
content: John, I have seen a bunch like that. I got stuck repairing some "refurbished" ELO touch screen LCD monitors for another program in the company. They were purchased as refurb but apparently done by the 3 Stooges. I found quite a few where there was only the base left and a scattering of material inside the monitor. Almost all the joints in question were cold/no solder joints, lifted pads from the rework and other foolishness. I haven't received a shipment of bad monitors for a few years now so, hopefully, those have been upgraded and sent to the scrap heap.