Andy Hill wrote:
PJx wrote:
On Thu, 07 Apr 2005 12:06:51 -0500, PJx wrote:

I think I will remove that component that is heat sensitive and
epoxy it to a cpu heat sink and hook it back up with wire.

Epoxy's a lousy heat conductor. Typically, you want some thermal
paste with some mechanical clamping.

Epoxy is a perfectly fine heat conductor for an application like this
(the charger was supposedly designed to keep the chip cool enough
without any heatsink), and I do include ordinary epoxy lacking any
particles intended to improve its heat conduction. Furthermore the
chip package itself is epoxy and will impede heat flow much more than
any thin layer of epoxy between it and a heatsink. Even a small
heatsink, like this one:


http://www.radioshack.com/product.as...%5Fid=276-1368

will likely at least double or triple the heat flow between the chip
package and the surrounding air, whether it's attached with ordinary
epoxy or silicone rubber adhesive (RTV).

Tool chargers typically fail when an electrolytic capacitor dries out
or the switching transistor shorts (MOSFET or bipolar, may be built
into the charging controller chip), and since cooling the hot device
makes your charger work again, I suspect a capacitor. Adding a
heatsink will not fix this but may prevent it from happening in the
first place. Any replacement capacitor must be rated for at least as
much voltage as the original and for approximately the same
capacitance. It's also important that it be designed specifically for
high frequency switching operation (low ESR). www.digikey.com and
www.mouser.com carry suitable replacements. The charging controller
chip is often made by www.maxim-ic.com or www.linear.com (their web
sites have schematics that may help you diagnose your charger), but
many use a general-purpose microcontroller (CPU), which can't be
replaced (but it should always have a separate switching transistor
that can be).

Chargers are not typically transformer isolated from high voltage, so
take great care when operating yours with its cover removed. At the
very least, plug it into a GFCI-protected wall outlet.