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About these pesky capacitors....
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Mike



Joined: 03 Feb 2017
Posts: 83
Location: Canada: Oshawa, Ontario

PostPosted: Sat Feb 25, 2017 9:01 am    Post subject: About these pesky capacitors.... Reply with quote

Mike here again:

As you may have gathered, I am relatively new to NexT hardware, having received a really nice clean complete NeXTStation system with a failing hard drive that has been replaced. The computer is (now) working perfectly.

As far as I can tell, it has seen very little use and has been handled gently and stored well.

Reading back through the archives on this forum I have been spooked by the frequent references to the capacitors in this and some other NeXT models.

How will I know if and when my capacitors fail ?

What are the symptoms ?

Will it simply stop working ?

I have examined the capacitors in this unit very carefully (and looked on the internet at lots of pictures of swollen capacitors) and mine show no indications of distress.

I have also looked at the brilliant NextStation Mono Logic Board images at: http://www.asterontech.com/Asterontech/nextstation_mono_retore.htm

Neat-o !!

Mike
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paolo.bertolo



Joined: 24 Sep 2015
Posts: 57
Location: St Gallen, Switzerland

PostPosted: Sat Feb 25, 2017 9:51 am    Post subject: Reply with quote

No experience with NeXT motherboards, I've replaced caps before they started giving troubles. On MO drives, faulty caps result into malfunctioning drives.
Worst thing that can happen though, is that leaked fluid damages the board and makes capacitor replacement quite tricky. Better replace them sooner than later.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Sat Feb 25, 2017 10:12 am    Post subject: Reply with quote

You definitely want to replace the caps if they start to spill cap goo. The SMD caps tend to do that. That stuff will eat up other components and traces.
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Mike



Joined: 03 Feb 2017
Posts: 83
Location: Canada: Oshawa, Ontario

PostPosted: Sat Feb 25, 2017 10:25 am    Post subject: Reply with quote

OK....

Thanks for the information and suggestions.

I have the pictures that show where all of the "caps" are on each type of NeXTStation mono board. I will identify my board type and diagram the locations.

I will make a point of popping the cover off the slab every couple of months and checking the suspect components for visible swelling, discolouration, and the board for signs of possible leakage.

If these "caps" have been in the computer for about 25 years without failing.... maybe they are immortal.

M
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Sat Feb 25, 2017 10:29 am    Post subject: Reply with quote

Nope. It depends on the quality but they will die at some time. Have a look at 68k Mac forums e.g. and you will see that this is a common problem of 80's Macs. I replaced leaking caps in my SE/30 and that machine is from 1989.
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paolo.bertolo



Joined: 24 Sep 2015
Posts: 57
Location: St Gallen, Switzerland

PostPosted: Sat Feb 25, 2017 11:26 am    Post subject: Reply with quote

Big, radial ones are easy to check visually, they tend to bulge and crack on the upper face, which is normally marked with a cross for giving an easy way out to the pressure building up inside the case.

My experience, though, is that they are usually lasting longer than surface mounted ones, unless they are operating at higher end of the temperature range (like those ones in the MO drives).

SMD are the nasty ones, I have replaced many, many of them on all my stuff (mainly late eighties / early nineties Macs and NeXT machines) and most of them were in poor conditions with fluid leaking out.

As long as you have some barely decent equipment and a steady hand, you just need some practice on a dismissed board before being able to successfully replace the caps on your NeXT machine.
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Sat Feb 25, 2017 12:43 pm    Post subject: Reply with quote

Is it necessary to replace the small ceramic caps? I thought they last virtually forever.
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paolo.bertolo



Joined: 24 Sep 2015
Posts: 57
Location: St Gallen, Switzerland

PostPosted: Sat Feb 25, 2017 3:35 pm    Post subject: Reply with quote

No, it is not. Actually, you should try to replace the SMD caps with ceramic or tantalum ones: since they are solid state, they last longer.
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t-rexky



Joined: 09 Jan 2011
Posts: 273
Location: Snowy Canada

PostPosted: Wed Mar 01, 2017 10:46 am    Post subject: Re: About these pesky capacitors.... Reply with quote

Mike wrote:
Mike here again:

Reading back through the archives on this forum I have been spooked by the frequent references to the capacitors in this and some other NeXT models.

How will I know if and when my capacitors fail ?

What are the symptoms ?

Will it simply stop working ?

I have examined the capacitors in this unit very carefully (and looked on the internet at lots of pictures of swollen capacitors) and mine show no indications of distress.

I have also looked at the brilliant NextStation Mono Logic Board images at: http://www.asterontech.com/Asterontech/nextstation_mono_retore.htm

Neat-o !!

Mike


You can read my original rant on the TurboColor capacitors here:

http://www.nextcomputers.org/forums/viewtopic.php?t=2803

Since your machine has likely no surface mounted (SMD) electrolytic capacitors your risk is much lower. <- Note per the posts below that this is not a correct statement. It is mostly the SMD capacitors of that era that are most susceptible to failure. Electrolytic capacitors are filled with a roll of sandwiched aluminum plates with a "wet" electrolyte solution. The electrolyte is either acidic or alkaline and is therefore corrosive. NeXT appears to have used at least two supply sources for electrolytic SMD capacitors. One of them appear to be "bad" and the other one "good" I have seen a number of TurboColor main boards and many audio box boards with both types. None of the "good" types have leaked on the units I have seen. All of the "bad" types have leaked, even on new old-stock audio box boards that have never been used.

The through-hole capacitors that your board is equipped with can fail in a similar way, but are much more durable and significantly less likely to experience such failures. Now, all electrolytic capacitors have finite life expectancy. But I have some test equipment manufactured by HP in early 70s that still has fully functional electrolytic capacitors. The more recent bad rap that electrolytics had was associated with industrial espionage where electrolyte formula with a missing key ingredient was stolen from a "high-end" Japanese capacitor manufacturer and the knock-offs manufactured elsewhere in Asia started swelling, venting and exploding after short time of use. That's the "capacitor plague" of a few years ago and is not related to normal electrolytic capacitor wear-out and aging.

As the electrolytics age in a "normal" way, they may lose their capacitance either through drying out or leakage. Loss of capacitance on the computer main board with result in increase in electrical noise. This noise increase may eventually reach a threshold where it will start affecting integrated circuits and may lead to unexplained behaviour, freeze-ups, crashes, etc. If the electrolytics in the power supply go, they may result in a somewhat more spectacular failures including a catastrophic power supply failure that could take out other computer components.

You can see a 20 year old SparcStation power supply that was very well designed and built, with high quality components, showing signs of capacitor failure here:

https://www.flickr.com/photos/t-rexky/albums/72157640695991374

In that album you can also see my rework of that power supply with all the electrolytic capacitors replaced by extremely high quality modern equivalents.

There was a question about ceramics. These do not need to be replaced as their life is effectively "infinite" compared to the electrolytics. Tantalum capacitors also have virtually "infinite" life in comparison and are often used as replacements for old SMD electrolytics. Polymer capacitors also last for extremely long time. All of this assumes, of course, that the equipment is well designed and the capacitors are appropriately de-rated for their application.


Last edited by t-rexky on Thu Mar 02, 2017 3:32 am; edited 2 times in total
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Wed Mar 01, 2017 2:29 pm    Post subject: Re: About these pesky capacitors.... Reply with quote

t-rexky wrote:
Since your machine has likely no surface mounted (SMD) electrolytic capacitors your risk is much lower.


Maybe I missed something but why should his NeXTstation have no SMD electrolytic caps?
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t-rexky



Joined: 09 Jan 2011
Posts: 273
Location: Snowy Canada

PostPosted: Wed Mar 01, 2017 4:10 pm    Post subject: Reply with quote

Looks like out of all board revisions only one has a single SMD electrolytic, while others have only through-hole electrolytics.
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Thu Mar 02, 2017 1:29 am    Post subject: Reply with quote

Sorry, my images might be misleading. I had already replaced the caps before taking the images. The green circles are where the SMD's would be. I've updated the site to mention this.
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t-rexky



Joined: 09 Jan 2011
Posts: 273
Location: Snowy Canada

PostPosted: Thu Mar 02, 2017 3:28 am    Post subject: Reply with quote

Well, that makes more sense now. I was wondering why NeXT would have used ceramics and why you'd be replacing them. I edited my response above to avoid confusion. Thank you for the clarification.
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wayne123



Joined: 13 Feb 2017
Posts: 10

PostPosted: Fri Mar 03, 2017 8:51 pm    Post subject: Reply with quote

What about the NeXT power supply caps. Is there any info on recapping them.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Sat Mar 04, 2017 3:34 am    Post subject: Reply with quote

There is info but the NeXTstation's psus are a pita to open.
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