On Mon, 10 May 2004 00:55:22 -0400, Dave McGuire <mcguire@neurotica.com> wrote:
> 
> On May 10, 2004, at 12:45 AM, Sean Davis wrote:
> >>    I do this sort of work all the time.  Is this a surface mount chip,
> >> or a through-hole?
> >
> > I'm not entirely certain. All I know (since I haven't taken the
> > motherboard out) is that it's mounted flush to the motherboard. I am
> > assuming by "through-hole" you mean it's stuck through holes on the
> > board and soldered on the back? If so, I'm pretty sure that's the
> > case: I don't see any solder near it on the board.
> 
>    Umm ok..."Through-hole" means there are holes drilled in the board,
> and the chip's pins stick down through those holes and are soldered.
> Usually you can see some solder on both sides of the board, around the
> pins.  A surface-mount chip is just that...its pins generally come out
> of the sides of the chip and fan out horizontally, and are soldered to
> pads on the board with no holes.

>    Most of DalSemi's chips are available in through-hole and at least
> one or two different varieties of surface mount packages.  Your first
> step will be ascertaining if the ones you got from DalSemi are in the
> same package as the one on your board, and then seeing if the pinouts
> of the two chips are compatible.

They are. DalSemi says they DS12887 is a pin-compatible replacement
for the DS1287, and the DS1287 in my alpha looks physically identical
to the DS12887 in my Pentium 66.

>    Argh.  Ok, I overcame laziness for a brief moment and downloaded the
> datasheets.  The DS12887 is only available in a through-hole package.

I was pretty sure that was what it was; I had just never heard the two
terms before; my electronics knowledge is limited to what I got in
high school ;-)

> Most people will say this makes it easier to deal with, but I work with
> both all the time and I think surface mount is FAR easier.  But no
> matter.  Assuming you don't want to save the chip you're replacing
> (it's dead, right?  otherwise why replace it?), the right thing to do
> is to use flush cutters to snip the old chip's pins as close to the
> chip body as possible, and remove the chip.  Then, using a hot,
> preferably temp-controlled iron, remove each pin from the top of the
> board with tweezers.

Okay. And it's not dead yet - I don't plan to replace it until it's
dead, but according to DalSemi, the battery is only supposed to last
somewhere around 6 years, and it's been longer than that since the box
was made.

>    Then carefully solder a socket (ALWAYS replace a through-hole chip
> with a socket) in its place, and plug the new chip in.

Very good idea (the socket)... I had not thought of that. And here I
was wishing it was a socket in the first place :-)

>    If you're uncomfortable with the idea of doing this, you can send the
> board and chips to me, along with a picture of a beer (I don't think
> it's legal to ship actual beer, is it?) and I'll swap 'em out for you
> and send 'em back.

It's legal to ship beer. But if/when I do decide to replace the chip,
I'd like to do it myself - valuable experience and what not. Not that
I wouldn't buy you a beer for providing very helpful advice, however
:-)

The only soldering iron I have right now is one of the gun-type, gets
extremely hot and is not variable-temp. So I would need a better one,
flush cutters, and a socket. I'm assuming I could find the right
socket either at radio shack or from DalSemi.

Thanks for the advice. The reason I asked is because (apparently) the
timeserver I use is out, and my Alpha was two minutes off, compared to
my Ultra 5 and my PC. They all run the same version of NetBSD, and all
use the same ntp.conf. When that chip dies (or more accurately, it's
battery dies) I know what to do now.

Thanks,
-Sean