Re: Lisa 1.8A Power Supply Problem

I would not advise repairing sealed electrolytic capacitors like these. Finding the right electrolyte could be very difficult, not to mention there could be small shorts in the cap (caused by small holes in the paper between the 2 pieces of rolled up foil) which this would not fix. I like to keep hardware 'all original' when possible too, but in my humble opinion, passive components like capacitors, resistors, pots, etc. are 'consumable.' You wouldn't drive a classic car on 30 year old tires, a blowout could cause a wreck and destroy more valuable parts, if you suspect bad caps in your 30 year old computer, don't run it on them either - better to have some 'un-original' capacitors inside a power supply than to have a capacitor fail and take out a bunch of logic or one of the transformers inside the power supply or something.

As for obtaining replacement capacitors, my usual strategy is to make note of the capacitance, voltage rating, temperature rating, and distance between pins of the capacitors I'm going to replace, and then search a mail-order electronics component supplier (here in the U.S, Digi-Key and Mouser are the big ones, not sure about other countries) for suitable replacements. Increasing the voltage rating of the capacitors is safe (and you may have to do this to get modern caps with the same spacing between pins), and I also like to replace 85 degree C rated caps with 105 C ones or better when possible.

Also, watch out for non-polarized electrolytics. These will have "NP" marked on them instead of the usual stripe on one side of the capacitor. I can't remember if the Lisa uses any (I think it doesn't but it's been a few years), but many 80s electronics with CRTs do, and the non-polarized capacitor cannot be replaced with a polarized one.

On Thursday, July 3, 2014 1:38:44 AM UTC-4, tommoni wrote:
>
> Hi Rudolf,
>
> it's definitely the Cap behind the primary rectifier.
> It's very likely that it has been drying, so if it gets powered up a part
> of the electrical energy can't be stored by the cap and will be transformed
> in thermal energy with the conclusion, that the cap will heat up a little.
> Pay attention: This status is short before the cap will "explode". You
> should not use the power-supply further more until you replaced that cap!
> As you know, I am a guy, who repairs Lisas with original parts so you get
> this advice: It's also possible to get this cap to work again; you only
> have to carefully open it by removing the rubber at the bottom, then fill
> in some caps-oil (I don't know the english expression for that fluid) and
> then the cap should work properly again. Be careful, sometimes the
> cap-making factories used Biphenyle, which can cause skin cancer.
>
> P.S. If it is not the circuitbreaker but the live-saving unit, which shuts
> off, then it should be the small cap (mostly 0,047 up to 0,22 mikrofarad)
> short after the power-plug.
>
> There are some other - but not very likely - part, which could cause such
> a fault, but first try this ones as written above.
>
> Tom, from Bavaria - the country of the Alps (as Austria, too), the
> marverllous castles of Koenig Ludwig and the original Octoberfest in Munich
>
> Am 02.07.2014 um 22:30 schrieb Rudolf Brandstötter:
>
> Hi guys,
>
> I have 2 1.8A PS with the same symphtom: when the PS warms up after 5-6min
> it shuts down. It looks like when it gets warm it does not work anymore.
> The circuit breaker in my house shuts down the power in the room. When the
> PS cools down after 1h it works again a few minutes. Do you know some
> typical suspects where I could look? I have a working PS as reference but
> I'm not really experienced in repairing PS. Thanks for any hint where to
> look!
>
> Rudi
>
> --
> --
> -----
> You received this message because you are a member of the LisaList group.
> The group FAQ is at http://lowendmac.com/lists/lisa.html
> To post to this group, send email to lisa..._at_email.domain.hidden
> <javascript:>
> To leave this group, send email to lisalist+u..._at_email.domain.hidden
> <javascript:>
> For more options, visit this group at
> http://groups.google.com/group/lisalist
> ---
> You received this message because you are subscribed to the Google Groups
> "LisaList" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to lisalist+u..._at_email.domain.hidden <javascript:>.
> For more options, visit https://groups.google.com/d/optout.
>
>
>

-- 
-- 
-----
You received this message because you are a member of the LisaList group.
The group FAQ is at http://lowendmac.com/lists/lisa.html
To post to this group, send email to lisalist_at_email.domain.hidden
To leave this group, send email to lisalist+unsubscribe_at_email.domain.hidden
For more options, visit this group at http://groups.google.com/group/lisalist
--- 
You received this message because you are subscribed to the Google Groups "LisaList" group.
To unsubscribe from this group and stop receiving emails from it, send an email to lisalist+unsubscribe_at_googlegroups.com.
For more options, visit https://groups.google.com/d/optout.



text/html attachment: alternate version of message