kaplanB wrote:
kaplanB had written this in response to
http://www.electrondepot.com/repair/...ce-126006-.htm

I reenter the discussion with a bit of trepidation as I'm am just a
pastor trying to fix his cooktop, not an
electrical engineer.

I have learned a LOT from your posts and this adventure. I think I
have learned enough to say that what
I'm trying to find a substitute for (Shindengen T30G40) is not an
IGBT or a NPN. It is a PNP! My thinking
is based on three main factors.

I've drawn my own schematic and the cooktop (Kenmore 564.4498512)
seems to look like a "quasi-
resonant" circuit I found when researching induction cooktop designs.
These designs use PNP transistor.

Second, the voltage at the base, measured on a working element, is
-56 Vdc when idle and -60 Vdc
when energized. Doesn't' that "turn on" a PNP transistor?

Not necessarily... You have to measure the base voltage in respect to the
emitter. Assuming that it's a silicon device, you should see -0.65V
to -0.8V at the base with respect to the emitter. That will turn a PNP
transistor on. If the difference in voltage between base and emitter less
than 0.65V, then the transistor isn't on.


Third, pulled the transistors off the board and one of the three power
transistors tests OK as a PNP.

Questionable assumption... How do you know the others are PNP units? Do
they have the same part numbers?


Kap B


Here's a quick spec on the T30G40 transistor:

Si NPN Power BJT
Shindengen Electric Mfg. Co., Ltd.
V(BR)CEO (V)=400
V(BR)CBO (V)=800
I(C) Abs.(A) Collector Current=30
Absolute Max. Power Diss. (W)=200
h(FE) Min. Static Current Gain=80
f(T) Min. (Hz) Transition Freq=7.0M
t(d) Max. (s) Delay time.=3.0u
t(s) Max. (s) Storage time.=3.0u
t(f) Max. (s) Fall time.=1.0u
Package=SIP
Military=N

That indicates that it's an NPN unit; not PNP. Are you sure that you're
testing the transistors correctly? Maybe you should post a quick narrative
on how you're trying to troubleshoot. And be careful that you know the
polarity of the test leads of the ohms function of your multimeter... A few
will fool you.

--
David
dgminala at mediacombb dot net