Mail Archives: geda-user/2012/07/14/04:40:04
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On 14/07/12 04:41, Edward Comer wrote:
> This is a bit off-topic - but - I am reverse engineering a circuit
> board so that I can make a new PCB with some changes. There are two
> surface mounted transistors in SOT23 configuration. One that is marked
> "t04" and using a multimeter, it tests out as an NPN transistor and I
> found some documentation that states that a "t04" is a PMBS3904 which
> is equivalent to a 2N3904. However, the markings of the second
> transistor are a mystery to me (It is marked "MON") and it does not
> test out as an NPN or PNP transistor. I suspect that it may be a
> MOSFET. Does anyone have any info on this transistor???
If it is a mosfet the gate should appear to behave like a small
capacitor (WRT one of the other pins). Do you have a capacitance meter?
Package markings on small packages are sometimes completely unrelated to
the ID of the part itself, ie batch/factory location/something else
that's really not very helpful to you... My favourites are the parts
with numbers sanded off...
Does the circuit still work? If so you could probably get a good idea of
the function of the part with a little careful observation of the
circuit in operation. Alternatively, have you ever come across a
transistor curve tester? These show excellent traces on a scope of the
behaviour of the UUT. I was trying to find you a link to a really simple
curve tester project, unfortunately I can't find it. Sorry...
Many things about the PCB design around the part might give you clues as
to it's type - some photos might mean we can help you better!
HTH,
Ed
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<div class="moz-cite-prefix">On 14/07/12 04:41, Edward Comer wrote:<br>
</div>
<blockquote
cite="mid:1342237267 DOT 98959 DOT YahooMailNeo AT web65902 DOT mail DOT ac4 DOT yahoo DOT com"
type="cite">
<div style="color:#000; background-color:#fff; font-family:arial,
helvetica, sans-serif;font-size:12pt">
<div><font face="arial, helvetica, sans-serif" size="3">This is
a bit off-topic - but - I am reverse engineering a circuit
board so that I can make a new PCB with some changes. There
are two surface mounted transistors in </font><font
face="arial, helvetica, sans-serif">SOT23 configuration</font><span
style="font-size: 12pt; ">. One that is marked "t04" and
using a multimeter, it tests out as an <span
class="yiv1570670070yshortcuts yiv1570670070cs4-visible"
id="yiv1570670070lw_1342234476_0" style="cursor: pointer;
color: rgb(54, 99, 136); border-bottom-width: 2px;
border-bottom-style: dotted; border-bottom-color: rgb(54,
99, 136); "><span class="yshortcuts cs4-visible"
id="lw_1342237169_0" style="cursor: pointer;
border-bottom-width: 2px; border-bottom-style: dotted;
border-bottom-color: rgb(54, 99, 136); ">NPN transistor</span></span> and
I found some documentation that states that a "t04" is a </span><font
face="arial, helvetica, sans-serif">PMBS3904 which is
equivalent to a </font><font face="arial, helvetica,
sans-serif">2N3904. However, the markings of the second
transistor are a mystery to me (It is marked "MON") and it
does not test out as an NPN or PNP transistor. I suspect
that it may be a MOSFET. Does anyone have any info on this
transistor???</font></div>
</div>
</blockquote>
<br>
If it is a mosfet the gate should appear to behave like a small
capacitor (WRT one of the other pins). Do you have a capacitance
meter?<br>
<br>
Package markings on small packages are sometimes completely
unrelated to the ID of the part itself, ie batch/factory
location/something else that's really not very helpful to you... My
favourites are the parts with numbers sanded off...<br>
<br>
Does the circuit still work? If so you could probably get a good
idea of the function of the part with a little careful observation
of the circuit in operation. Alternatively, have you ever come
across a transistor curve tester? These show excellent traces on a
scope of the behaviour of the UUT. I was trying to find you a link
to a really simple curve tester project, unfortunately I can't find
it. Sorry...<br>
<br>
Many things about the PCB design around the part might give you
clues as to it's type - some photos might mean we can help you
better!<br>
<br>
HTH,<br>
Ed<br>
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