Re: [CAD_CAM_EDM_DRO] Replacing transistor in burned Gecko

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?
>
>

If totally in doubt, pull all the transistors. (Note there is also one
similar looking device that is the voltage regulator. leave it in.
It will have an LMxxx part number.)

With the transistors out, the metal face down and the leads facing you,
the leads are, from left to right : Gate Drain Source. Check that the
gate lead reads infinity ohms to both Drain and Source. If you don't get
infinity on BOTH tests, throw the part out. Now, use a clip lead to
connect drain to source. Read resistance from drain to source, but
put the ohmmeter's positive lead on the drain. You should read
infinity, or very close to it. If it reads under a megohm, it is definitely
bad. If over a megohm, it might just be dirty. Now, this check it
tricky, and may not work with all meters. Remove the connection
between source and gate. If you have a diode check
mode on your meter, use that instead of the Ohms range. Connect
the negative lead to source and leave it there. Touch the plus
probe to drain, and read the voltage. Then, move the plus probe to
gate, and then back to drain. See if the voltage is
lower, indicating the transistor is conducting. If it is, that's a good
sign.

A Gecko 201 or 210 has 8 of these transistors. A Gecko 320 or
340 has 4.

Jon