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576 CT no step generator current but voltage steps OK


Ed Breya
 

I recently tried to check some transistors but found the 576 isn't delivering base current steps. My most recent use was on some JFETs, which worked fine, with voltage steps. I mostly do I-V checking, and seldom bipolar transistors, so I have no idea how long ago this function crapped out.

I'll have to pull it off the bench and go through all the grief of handling and opening up this beast and digging into the guts. Before I do, I'm wondering if anyone has experienced this particular problem, and if maybe it's something simple, like a pulled connector or such? Or, is there anything in the plug-in test fixture that could cause this? It would be a lot easier to yank the fixture and work on just that, of course. I've worked on these plenty of times, and expect the diagnosis and repair will be OK, unless it's something deep inside and hard to access.

Ed


William Borrero
 

I would say your best bet is to check your switch contacts which are likely
dirty. Sometimes just operating them can clear the problem. Focus on the
Step Generator section first.

On Tue, Sep 29, 2020 at 6:48 PM Ed Breya via groups.io <edbreya=
yahoo.com@groups.io> wrote:

I recently tried to check some transistors but found the 576 isn't
delivering base current steps. My most recent use was on some JFETs, which
worked fine, with voltage steps. I mostly do I-V checking, and seldom
bipolar transistors, so I have no idea how long ago this function crapped
out.

I'll have to pull it off the bench and go through all the grief of
handling and opening up this beast and digging into the guts. Before I do,
I'm wondering if anyone has experienced this particular problem, and if
maybe it's something simple, like a pulled connector or such? Or, is there
anything in the plug-in test fixture that could cause this? It would be a
lot easier to yank the fixture and work on just that, of course. I've
worked on these plenty of times, and expect the diagnosis and repair will
be OK, unless it's something deep inside and hard to access.

Ed





--
--
Best Regards,

Bill B.
Solutions that make sense.


Albert Otten
 

Hi Ed,

Please ignore this if you tried already.
Set the left-off-right switch to off, steps to 1, base current at 10 uA steps, horizontal at base voltage 2 V/div. The base voltage choice terminates the base current in 1 M. So you should see a dot at 0 V and a dot at 10 V. If you increase the number of steps you will note compression above 12 V or so.
The test fixture is not involved, unless it leaks B to E somewhere, very unlikely in OFF position.
I don't know where base voltage is sensed internally. If you see the same check result when you choose Left or Right and short B to E there, there likely is an interruption between sense point and B terminal.

Albert

On Wed, Sep 30, 2020 at 12:48 AM, Ed Breya wrote:


I recently tried to check some transistors but found the 576 isn't delivering
base current steps. My most recent use was on some JFETs, which worked fine,
with voltage steps. I mostly do I-V checking, and seldom bipolar transistors,
so I have no idea how long ago this function crapped out.

I'll have to pull it off the bench and go through all the grief of handling
and opening up this beast and digging into the guts. Before I do, I'm
wondering if anyone has experienced this particular problem, and if maybe it's
something simple, like a pulled connector or such? Or, is there anything in
the plug-in test fixture that could cause this? It would be a lot easier to
yank the fixture and work on just that, of course. I've worked on these plenty
of times, and expect the diagnosis and repair will be OK, unless it's
something deep inside and hard to access.

Ed