Electrolytic Capacitors--Problem on Amiga Circuit Boards?

[aardvark]

While looking on the web for recommended ways of cleaning motherboards, I stumbled across this site.

While battery issues on Amiga circuit boards are well known and the fixes documented, do we have similar problems with capacitors?

If so, outside of obvious leakage, how do you test them while they're still on the board? :-?

[Holley]

Holy cow, thats thorough!  I've never heard of capacators causing damage, but then my experience is limited - I've only restored a hanful of Asteroids boards that my Dad found in his shed (he used to run some arcade machines).  I'd say leakeage would come way after failure on something thats used regularly :-?

[alx]

do we have similar problems with capacitor

I'm not a h/w person, but isn't there a problem where the audio can die on an A4000 due to a leaky capacitor :-?

[nOw2]

This look suspiciously like something on my A4000D motherboard..

Story: the clock on my A4000D doesn't tick, and all around the RTC circuit is a thin film which I had assumed to be from the old battery (long replaced). The area is also populated by lots of capacitors like those in the photos.. The machine used to work fine after one reboot but hasn't for some time now.

A few nights ago, prompted by just-amiga users, I had another look at it. A quick look with my new multimeter (took me years to get around to buying one, but it's invaluable! Everyone should get one if they deal with computers!) showed that the traces I thought were bad, were actually fine! No obvious circuit breaks anywhere.

So, I had a little play around - there's actually a variable capacitor on there, and after a little playing I found that one turn anti-clockwise got the machine working at least on some boots.

Now, reading that webpage and seeing the similarities, noting that changing a VC made some difference, and that the machine used to work after a warm boot (slow charging caps?) I think we might have discovered the root problem my A4000 has!

To sum up, I think this problem may well be affecting some Amigas. But, unlike the battery problem, capacitors don't leak acid and ruin the machine totally (at least, I hope not..)so this is ultimately repairable. Hmm, I wonder how many Amigas have been landfilled with a problem which is repairable? Doesn't bare thinking about.

[aardvark]

I found another web page which talks about capacitor problems on motherboards here.
They also refer to here and to a Toronto Star article here.

Perhaps most of our circuit boards predate the faulty capacitors, but then again.... :-(

[Noster]

Hi

The capacitors-problem seems to be a problem of the modern very hot running PeeCee Motherboards with the CPU's that require much power. :-D
I have a couple of old Amiga computers -- from A1000 upto A3000T -- and my 12 years old A3000T runs several hours every day without any problem in the last 12 years (except a defective 8520 and a renewed battery).

The german C'T computer-magazin has reported a few times about these capacitor-problem. It seems that there is at least one charge of a few millions of capacitors produced with bad electrolyt. When these capacitors work in a very hot environment they burst in less than 1000 hours of usage instead of 10 or more thousend.

Noster

[nOw2]

aardvark, I've not seem any of those type of capacitors fail on an Amiga. Certainly, the make & type they talk about hasn't even been used on one AFAIK.

I do have a PC here with a Gigabyte mb (from 2002) full of buldging capacitors around the CPU. I have run the machine rather warm (it spent last summer with the case temperature at 50C+ and the year before with the CPU at around 75C), but that's well within spec so you'd expect better really..

[QuikSanz]

Hi,

Actually, they can fail if it has been stored for a long while with no power up. They can "dry out".

Chris

[Tomas]

QuikSanz wrote:
Hi,

Actually, they can fail if it has been stored for a long while with no power up. They can "dry out".

Chris

I wonder if this happened to my c64... I had a c64 that was in perfect order, then stored it for a couple of years in my closet, but when i decided to fire it up again, there was only black screen..  That machine ended up on the scrapyard..  :-(

[macto]

I am aware of the Toronto Star article in question.  The issue in that case was a company using a bad "recipe" for the dielectric.  Computers were dying on the order of months and it hit several major manufacturers.  The article claims that almost everybody was trying to cover the problem up.  But this was recent history, and it wouldn't impact old Amigas.  I have run into this sort of problem before.  For example: a vital data storage technology of the mid-1980's (tapes) started failing on the order of months when manufacturers started using a different "recipe" for the binder which attached the recording surface to the supporting substrait.

Another problem is that capacitors do not age well.  My understanding is that they have a life expectancy of twenty years of so.  Of course some will die sooner and some will die later.  The variability may be the product of the manufacturing process (ie. not all capacitors are created equal) or of how the machine is treated.  Some people call this drying out and some people call it leaking.  It is commonly refered to as leaking in the Compact Mac world because cleaning it in a dishwasher often clears up the problem.  The suspected cause is that the dielectric is causing shorts on the circuit board. That doesn't make much sense in my mind because dielectrics are not supposed to conduct!  On the other hand, I do not know much about the operation of electrolytic capacitors.

@Tomas: We are eventually going to have to develop better ways of "repairing" our machines.  While we can be frivilous today, the process of decay is only going to become worse.

[QuikSanz]

Hi macto,

leaking is one thing, it leaves behind clues associated with thermal breakdown. Drying up shows no bulges or leaks, the dielectric has just given up. Having collected much old audio equipment, some tube stuff too, I've seen this before starting many years ago, long time..
When storing something, power it up once in a while.

Chris

[Floid]

nOw2 wrote:
aardvark, I've not seem any of those type of capacitors fail on an Amiga. Certainly, the make & type they talk about hasn't even been used on one AFAIK.

I do have a PC here with a Gigabyte mb (from 2002) full of buldging capacitors around the CPU. I have run the machine rather warm (it spent last summer with the case temperature at 50C+ and the year before with the CPU at around 75C), but that's well within spec so you'd expect better really..

You should really contact Gigabyte about a RMA, as if they did use the bad 'batch,' better to find out if they'll cover your shipping now than deal with an unexpected failure.  Worth a shot, anyway.

I'm surprised nobody mentioned the mis-installed capacitor issue on the... 4000, was it?... That'd have similar symptoms, but for a correctible 'reason.'  Now I have to find the link...

[Floid]

One link on the 4000/3640 issue here; searching the forums should dig up more info.

[Noster]

Hi

@nOw2

>  have run the machine rather warm (it spent last summer with the case temperature at 50C+...

That is very hot, you should add an additional fan to cool your case down! Intel recommends case temperatures below 45C and AMD below 40C, otherwise the CPU cooler cannot cool your CPU good enough, it may overheat.

Unfortunately there is no known maximum case temperature specified for the Amiga, but I think many problems with the CyberstormPPC cards are temperature problems, either a defective CPU-fan, a case that is too hot or maybe bad capacitors.
I have replaced the CPU-fan by a 12V 486'CPU-fan, and added two more fans in my A3000T case to cool it down. It has previously reached 50C an more in the sommer at a room temperature around 26C. Now it stays below 40C :-D.

@everybody

Have a look at your capacitors. Usually there is a temperature printed on them. There are two mayor types a 110C type and a 80C type (I think). The capacitors are specified to work 2000(!) hours by these temperatures (not a long time-period in my thought, but they work longer if these temperatures are not reached). If they have a bad electrolyt inside and the manufacturer build in the cheap 80C type and the system is running hot (as the system of nOw2) and a couple of hours every day, these capacitors can blast within one year :-(
Especially if you look where these capacitors are usually mounted: Direct in the hot air blown from the CPU cooler.

Noster

[Brian Hoskins]

There is a problem with the A4000 machines where some surface mount capacitors go faulty, normally causing intermittent or no audio output from the standard RCAs at the rear.

In a worst case scenario, the caps actually leak electrolyte all over the surrounding PCB, and I saw an A4000 whose PCB pads had actually been disintegrated which made replacement of the capacitors nearly impossible.  I attempted the repair and only found limited success.

Electrolytic capacitors do have a short life, relative to other types of capacitors - it's one of the disadvantages to using them in designs.  But I don't think Commodore ever envisgaed that we'd still be using their machines 10 years after the bankrupcy!! That means most of our machines are over a decade old, and unfortunately with that kind of age they're ripe for electrolytic capacitor failure.

To add to the misery, I think the main cause of the cap failure in the audio part of the A4000 board was due to Commodore sourcing a cheap batch of Capacitors whose quality wasn't as good.

Generally, I think serious Amiga users should now be keeping an eye on their motherboards.  If a problem is spotted early enough, it can normally be recitified quite simply.  If it's left to it's own devices, the leaking electrolyte causes damage to surrounding components which may cause a write-off motherboard :-(

People need to be checking for bulging or leaking electrolytic capacitors!

Brian