A4000 getting flaky- need a quick checklist

[CRL]

Hi All-
My A4000 (stock internally except for Sonnet quaddoubler 68040(50mhz)) has been running ontinuously for most of a year. In the last week it has frozen up every time I turn it on after about an hour or so.  I cleaned out the battery a year ago.  I haven't added any new softwear.  I did blow the dust out of the fans, but that made little difference.  If I was getting guru meditations I might have some clue, but the solid freeze has me spooked.  (I left it running because my cheap add-on flickerfixer/scan doubler wouldn't stablize until it had been running for 5 minutes or so.)

A few ideas to try or things to check would be appreciated.
CRL

[Chain]

definitely clean cpu connector first

[TjLaZer]

Check the area around the battery leakage, it could of been eating away the past year possibly ruining some traces!

[Zac67]

- CPU slot connector
- battery leakage
- PSU (voltages, maybe ripple)
- electrolytic capacitors (leakage, bulging)

[rkauer]

Zac67 wrote:
- CPU slot connector
- battery leakage
- PSU (voltages, maybe ripple)
- electrolytic capacitors (leakage, bulging)

 PSU ripple is caused by bad caps, and electrolytic caps can die without bulging. The simple answer (if you do the firsts steps and have a no-go) is: change the caps! It's inexpensive.

[HammerD]

@Zac67

How long do those capacitors last? The short silver/black ones? And do they die quicker if you use the computer more? If your Amiga isn't turned on for awhile do they still "age" and potentially leak?  Just curious!

Thanks

[Zac67]

The lifetime of electrolytic caps depends on their temperature rating and their actual operating temperature.

Operating them at their rated temp will fail most types after 2000 hours, any 10°C lower doubles that. E.g. a 85° type run @40° should last appr. 2000 x 2^4.5 ~=45,000 hours (~5 years 24/7). If you mismatch polarization (like on the A3640 or the audio circuits), the cap will die much sooner, depending on current. Of course, running a badly ventilated and hot system will have a bad impact on caps life, as well as loading them with high currents (you need low ESR types for that). Some caps used in PCs and other equipment are filled with bad electrolyte and fail after only a few months or years.

You could just use that rule for not-in-use/stored caps with, say 25°C, but I think they age a lot slower when not in use.

Anyway, it's a good idea to only use 105° caps for anything valuable.

[HammerD]

@Zac67,

thanks for the detailed info.  On my A4000 desktops and on my A4000T all of the caps look to be in good condition.  The A4000T was manufactured 1997 but is not turned on that much - the board looks in "new" condition...so I hope it lasts alot longer

The A4000's have been used more but the caps still look good...knock on wood...hopefully they last a few more years The room temperature in my apartment is normally around 19-26C depending on the season.  Right now because we are getting closer to winter (first snow fall today!) it's around 20C...

[rkauer]

 Other variables exists in cap's util life: humidity level, for example.

 A place where an air-cooling system is on most the year can dry the electrolitycal innards.

 The better move is swap'em all each 3~5 years.:hammer:

 

[CRL]

Hi All-
Thanks for the checklist.  I finally took off the lid and started it up to see what I could see (I wondered if the muffin fan on the quaddoubler had quit and let the CPU overheat), and discovered that the fan in the PSU had frozen up.  Looks like I will have to replace it and maybe do a preventative replace on the capacitors as well.(?) An overheated PSU could account for the symptoms if I read the checklist correctly.  I have done some electronic hobby building about 40 years ago, but nothing since.  Anything I need to watch out for as I dig into the PSU?
Thanks for the help- this comunity is the greatest if not the crazyest!
CRL

[rkauer]

CRL wrote:
Hi All-
Thanks for the checklist.

 You're welcome!:-D

 Anything I need to watch out for as I dig into the PSU?
Thanks for the help- this comunity is the greatest if not the crazyest!
CRL

 Just the caps! :roll:

[CRL]

Hi All-
Just a note to say my A4000 is running again.  I found an exact replacement muffin fan at Radio Shack (pricy, but oh well).  Blew out 14 years worth of dust and everything looked shiny, clean and OK.  No bulging or sagging or melting or brown colors from heat.  The big PSU caps were rated for 85C and looked like new.  I put in the fan, reassembled the PSU, the computer, and it ran fine.  I did break the flimsy and brittle power switch on the PSU, but I never used it anyway.  Thanks for the suggestions of where to start.  Thought you guy would like to know there is one more Amiga amoung the living.
CRL

[Dandy]

Zac67 wrote:

...
You could just use that rule for not-in-use/stored caps with, say 25°C, but I think they age a lot slower when not in use.
...

Hmmm - some years ago I repaired an old radio (build somewhen in the late 1920ies), that a friend had found in his attic.

It had two large electrolytic caps (like the starting capacitors in washing machines) that were defunct and caused the radio to grumble when turned on.

It took me nearly half a year to find replacement for those beasts, and the salesperson recommended to switch the radio on at least every few weeks to avoid the electrolytic caps to dry up again (that's why the old ones were defunct)...