Re: Recapping a power supply

>I have a broken 1.2 amp power supply, and I thought I'd try
>recapping it in hopes that I can make it work again.

For a little background info, see also:

   http://lisafaq.sunder.net/lisafaq-hw-pwr_identify.html

and:

   http://lisafaq.sunder.net/lisafaq-hw-pwr_repair.html

>C1-C4 are some kinds of AC filtering caps, and I'm not quite sure
>what they're called or how to find them on electronics components
>sites.

The key characteristic of these is that they are "safety rated" filter capacitors. This is a nice brief description:  

http://www.illinoiscapacitor.com/pdf/Papers/EMI_RFI_suppression_capacitors.pdf

So for any of those capacitors that have an X on them, you want to find at least a "Class X2" replacement. eg.  

http://www.digikey.com/product-search/en?keywords=%22safety+rated%22+%22film+capacitor%22&stock=1

However, in the design of this particular power supply, C3 and C4 are connected to ground, so by current standards, these should actually be Y rated capacitors.

It appears the original X rated caps having translucent yellow cases often fail once the cases become cracked, so replace all the cracked ones (if not all of them).

As with other capacitors, you can substitute one with a higher voltage rating if an exact substitute is not available. The physical size of capacitors decreases as improvements are made, so you may have to use one with a higher voltage rating if current ones of the same rating are now too small to fit.

>C12 and C13 are enormous and have four leads each-and it looks like
>there are holes in the PCB to accommodate up to 5 pins.

These capacitors have extra leads only for mechanical stability (eg. for shipping durability), and can be replaced with two lead capacitors, preferably with a glob of something to hold them together and/or to the circuit board.

I believe these are the most common point of failure for these power supplies. Using the highest temperature rating available for these will extend their life. You can also choose ones with a higher hour (lifetime) rating.

For this power supply:

The larger output filter capacitors (C14, C15, C18, C19, C20, C21) are also likely failure points and to a lesser extent, C9, C10, and C27, C28.

Other common points of failure are the main rectifier CR11, and the switching transistor Q1.

James

-- 
-- 
-----
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.