Re: [CAD_CAM_EDM_DRO] Replacing transistor in burned Gecko

You can often spot the dead transistor by looking at the case. If the
plastic has cracked or blackened then it is dead. Otherwise use a meter
as Tony suggests. Always replace the transistor opposite as well. If one
is gone it's opposite partner is almost undoubtedly dead or dying.

The easiest way is to remove them is to cut the legs off close to the
case, heat each leg up in turn and pull it out. Apply the heat from the
same side you are pulling from. The circuit board acts as a heatsink
so you need to use a reasonably hot iron to get enough heat in to melt
the solder.

Once the legs are out, apply a small amount of solder to each hole then
gently clamp the board vertically. Apply heat on one side and a solder
sucker (sometimes called a solder pump) on the other side. Wait a couple
of seconds for the heat to travel through the hole then trigger the
solder sucker. If you are lucky the hole will clear completely. If not,
apply solder and try again. You cannot clear a half-empty hole.

When these transistors go they often fry the driver chip (IR2104S if I
remember correctly) so it is worth replacing it as well. I have found a
good way of removing these is to very gently cut the legs off the case
using a sharp knife or chisel. Apply a steady downward pressure and rock
the chisel side to side until all the legs are cut. Now apply some
liquid flux (electronics flux not Baker's fluid!) and wipe the legs of
the board with a soldering iron.

To fit the new chip, apply plenty of liquid flux, carefully position the
chip and heat up each leg in turn. There is usually enough residual
solder on the pads to create the joint. If you get any solder bridges,
clean them off with some solder braid. Clean the board and hopefully you
are in business.

When testing a newly repaired drive, first leave the motor disconnected
then apply about 24V to the power input with a light bulb in series to
limit the current (24V 21W is ideal). If the bulb lights or something
gets hot, turn off immediately. If all is well then turn off, set the
current to a low value (say 2 amps) and connect your motor. Turn on
again. If the bulb does not light or lights dimly then try stepping the
motor.

Les

onecooltoolfool wrote:

>
> Is it worth the effort to try and replace a burned transistor in a
> Gecko drive? I bought a handfull of these thinking I would try it
> but after looking at the board I was intimidated, so there it sits
> for several weeks.
> And how do you know which one is bad?
> Joe V.
>
>
>