Serial Boards

[John F. Haugh II]

In article <2657 at nuchat.UUCP> steve at nuchat.UUCP (Steve Nuchia) writes:
>To safely replace the UART it needs to be socketed; I've got internal
>modems that have surface mounted 8250s and I understand that the telebit
>internal has an 8250 soldered down.  Oh Well.

Adding sockets to unsocketed boards is a snap if you know the right
procedure.

All of this should be performed with your body suitably grounded, and
a fine pointed soldering iron.

Start by cutting the leads off of the old chip with a pair of narrow
tipped cutters.  Take a low wattage iron, 15 or 20 watts is plenty,
and tin the tip well.  Grasp each piece of left over lead with a
pair of needle nose pliers, hemostats work perfectly for this.  Then,
heat the solder side of the board with the iron.  The lead should
come free in a few seconds.  The trick seems to be keeping the tip
of the iron clean and well tinned.  Remove all leads before beginning
the next step.

Prepare the board for the socket [ or a new chip ] by removing the
solder from the holes.  If you are fortunate enough to have a solder
sucker, you will know how to do this already, otherwise, you can
remove the solder by placing a piece of copper solder wick between
the board and the iron, and then heating the wick.  You need to use
fresh spots on the wick after each hole.  Avoid leaving the iron in
one spot for too long to prevent ruining the board.

With all of the holes cleared out, insert the socket or new chip [ I
suggest replacing any soldered in chips with socketed chips ] into
the holes.  A trick I use is the bend over pin 1 and the pin
diagonal to prevent the item from falling out.  Using very fine
gauge solder, solder each pin to the board.  You want to use fine
solder [ 24 gauge or smaller ] so you won't have to heat the solder
for too long.  Always proceed with this step SLOWLY, allowing several
seconds between each joint to reduce the likelyhood of heat damage
to the chip.  Of course, if you are installing a socket this advice
doesn't apply.

Finally, if you just added a socket, insert the chip into the socket
as you would have if the original chip weren't soldered in place
originally.

No big deal.  Surface mounted goodies are a different story ;-(
-- 
John F. Haugh II                        +----Make believe quote of the week----
VoiceNet: (214) 250-3311   Data: -6272  | Nancy Reagan on Artifical Trish:
InterNet: jfh at rpp386.Dallas.TX.US       |      "Just say `No, Honey'"
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