"Gareth Magennis" wrote in message
...


"Phil Allison" wrote in message
...

"Gareth Magennis"
"Phil Allison"


I recently bought some TIP35C transistors from Farnell UK. Just before
I fitted one to an amplifier I thought I'd just check the pinouts.
Good job I did because instead of BCE they measured BEC.


** That is just not possible.

The middle leg is always the collector and metal tab used for
heatsinking.

FFS - get an ohmmeter and verify that simple fact.

Seems your dopey microprocessor ( ie software) based POS has gone ape
and confused Collector with Emitter.



I did suspect my dopey checker, but even with a fresh battery it ALWAYS
reads EXACTLY the same,


** ROTFL - since when is THAT any reason to trust it ?????

" It must be right cos it always tells the SAME lie "

Wot an idiot you are.


which is: 3 of them measure BEC with an Hfe of 5, the other one BCE with
an Hfe of 20.

** No fooling.

BJTs have very low Hfes if C and E are reversed.

Like 2 or 3 instead of 100 or 200.

They *also* show very low readings if the meter is no ****ing good.

See how that might be confusing ???


(All tabs connect to centre pin)


** Then there is simply **NO** problem with the devices.
-------------------------------------------------------------------

YOU are the problem with your dopey meter that is not able to tests power
BJTs properly.

FYI Try it with a TV horizontal output transistor like the BU208.


The replacements I finally got from Farnell with a different batch code
measure an Hfe between 40 and 70.


** Testing the Hfe of *power transistors* is a whole DIFFERENT ball game
to small signal devices.

That is why I designed a special device just for power devices -
published as a project in Electronics Australia magazine in May 1988.

Test are done at a constant Ic of 0.6 amps instead of some fixed and way
too small Ib.

Results are spot on and match maker's data which follow the same idea.

Works fine with TV horizontal output devices, power darlingtons and any
BJT rated for high power.



I know Hfe is kind of meaningless on these types of checker voltages, but
was still wondering why the checker would give a different pinout result
rather than fail the device.

** Cos it is using the wrong approach for power BJT devices.

I suspect all 4 of the "old" transistors are faulty,

** ********.

You have a ******ing useless** meter that only works with those examples
of power BJT devices that exceed maker's specs at the low end of the Ic v
Hfe range.

Take a LOOK at some ACTUAL power BJT data sheets some time !!!!!!!!!

Hfe is NOT a constant !!!!!!!!!!!!



.... Phil





Yes I know Hfe is not constant, that is why I said the reading is
meaningless on such a low voltage checker.

I do not use this device to measure Hfe, I don't usually give a **** what
the Hfe of a transistor is, I assume all new ones I buy from Farnell are
within manufacturers spec.
I usually just want to know if a transistor is bad, what pinout it is, and
whether or not it tests on this meter in the same ballpark as a known good
one.

These 4 "faulty" transistors do NOT test in the same ballpark, they probably
DO exceed the maker's spec if they work properly at all. In that respect
the tester has done all I have asked of it.

I am not going to put one of these devices into a Power Amp (which I was
about to do before I tested them) and have it blow up in my face. Farnell
can damn well send me 4 good transistors which ARE in the right ballpark,
which is exactly what they have done, one of which went into the Power Amp
which did not blow up in my face.



Cheers,


Gareth.


The first tests to do on a suspect Transistor is using the Diode test mode
on a DMM (assuming there are no cracks in its case or plastic blown off -
that lets out the magic smoke). Start testing across two leads at a time,
go forwards (the red lead on one pin and the black on another) then reverse
polarity (black to red). Try all three variations. On a good transistor you
should get about 0.6 volts across two sets of pins, one of them being common
between the two, that is the base lead. When you reverse the leads it should
read OL on your DMM. From there you can determine if it is NPN or PNP
transistor. If one reading shows about 1.2 Volts and OL in the reverse
direction, its a working darlington transistor. If you read a short or
readings in forwards and reverse, then the transistor is NFG. Google the
part number, it is very easy - You will find pin outs, datasheets on almost
anything.

Shaun