On Mar 1, 11:08 am, Matt <[email protected]> wrote: > It is a frequent topic of conversation here but is there a well > documented process for replacing bad capacitors in these machines? > Any tips, tricks, advice or stories? > > What is some suggested practice before performing this on a > once-trusted machine? I have worked with a soldering iron before and > assembled electronics kits from components but this seems to be a bit > more high stakes.
I assume you mean surface mount electrolytic logic board capacitors and not the large axial or radial capacitors found on the analog board of the Plus, SE and Classic. This has been discussed extensively over on the forums at 68kmla.net. The difficult part is removing the old capacitors and there are several methods favored by different folks, but since, I'm replying, I get to post my favorite. The basic procedure is: 1) Identify the old caps to remove. 2) Make a list of their locations and values, obtain replacements. Tantalum caps make a good replacement for old surface mount electrolytics. 3) Remove all the old capacitors. Clean all the solder off of the old pads. 4) Thoroughly clean the board. Use solvent (e.g. isopropyl alcohol). Some use hot water in a dishwasher. Reports are that it works, but it makes me nervous. Rinse with distilled water. Dry thoroughly. 5) Inspect board for damage. The leakage from electrolytic capacitors is corrosive. 6) Repair any damage. 7) Install new capacitors. 8) Test. If there are problems repeat steps 5 & 6. The damage caused by corrosion can be visually very subtle. Regarding removing the old caps. The difficulty is that the surface mount capacitor has two terminals and the solder must be melted on both simultaneously in order to remove the capacitor. Here's the instructions I've posted elsewhere (I got the idea from Marc Schrier's Clock Chipping Home Page many years ago): In my experience, the easiest way to remove the old caps is to use two soldering pencils at one time. That way you do not put mechanical stress on the circuit board (as you do when you heat one side at a time). A grounded 15 watt soldering pencil is available from Radio Shack for under $10. So, if you already have one soldering pencil, go pick up a second one and make this job easy for yourself. If you try to use just one pencil, by the time you can heat the second pad, the first will have cooled. With the one-pencil-method you are forced to either get the entire cap and board so hot that the solder will stay melted while you move the pencil from side to side, or you end up bending the cold solder on one side, while lifting the other side. That over-heating and/or bending is what typically leads to lifted pads on the circuit board. With the two pencil method, you just apply a pencil to each end of the cap to be removed and wait until you can gently lift the cap with little to no resistance. It's useful to have a damp sponge on hand, as sometimes the cap sticks to one pencil tip or the other and it can be wiped off on the sponge. Jeff Walther -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
