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This is a good question for TekScopes so I’m forwarding it on to the forum
to see what they think

Hi Sean,

There shouldn’t be more than a few microamps of current for the zero step of
a 2N3906. 100 milliamps is a huge offset. I suspect there is a problem with
the 577 or there is an internal calibration step you should find in the
calibration procedure that explains how to zero that out.

As an experiment, if you enable the variable offset what do you have to do to
get the 0 step down to 0 on the curve tracer?

Dennis Tillman W7pF

From: Sean Turner
Subject: Curve tracer setup question...wrt PNP transistors

Hey Dennis,

I was wondering if you can help me understand something about my 575 and PNP
transistors. I found the following document (
) which essentially lines
up with what the 575 manual tells you to do for setting up the display, though
they are talking about NPN in both cases. I have found this technique to work
well for NPN transistors; the results agree generally with my 577D1 with the
offset in “zero” mode (button IN). However, this is not the case with some
2N3906s I’m trying. On the 577, it shows a small amount of leakage current
on the zero step (no offset selected at all; the zero button pushed IN).
Generally ~100 mA. However, on the 575, if I follow the setup procedure, it
shows none since I zeroed it out with the step zero control in the process.

So, how do I get the 575 set up to agree with the 577 here? Which one is
right? Maybe they’re both wrong? Maybe I’m an idiot (entirely possible)?

Any tips and tricks much appreciated!

Thanks!

Sean

Hi Sean,

I remember now. My 7104 spends most of its time, all dressed
up, with no place to go... So, it is not one of the scopes that
I am most familiar with.

If you look on the front panel, you will see an outlined area that
has two intensity pots (A and B), a READOUT intensity pot, and two
push buttons for the readout.

The one button is marked +GATE or OFF, and sets the readout to be on
at the end of the GATE signal, or off. The other push button is
marked "MAN", which causes the readout to be on always.

Something there is probably in the wrong position, or misbehaving.

Also, I keep my plugins off of AUTO on my 7104. Because of the
MCP's limited life, you do not want to be wasting it with continuous
readout display, or baseline display. I keep my readout in "GATE"
mode, so it is off if the sweep isn't being triggered.

Typically, I also keep the A and B intensity turned off when the
scope is off, to avoid intensity flair during turn on.

-Chuck Harris

I have sometimes had to drill out the set screw. The damaged hex recess
provides a guide for the drill bit.

I use a left-hand drill in my vertical mill where I can easily reverse
the rotation direction. Left-hand drills are available in a full range
of sizes, down to #80. I often find that in drilling the hardened set
screw that the drill will catch in the screw enough to actually loosen
the setscrew.

Even if that does not happen, you can increase the size of the drill bit
and eventually remove so much set screw material that is is too weak to
retain itself. Just don't use a drill larger than the minor diameter of
the internal thread in the knob.

This approach with left-hand drills works in many kinds of stuck
fasteners. One of my local machine tool dealers has a cabinet full of
left-hand drills; I went through it and picked out a bunch of sizes to
keep on-hand.

I have hex keys in Imperial Inch and metric, and Bristol with different
numbers of flutes depending on size. There is no Torx that small that I
am aware of. I often work on microscopes and some cameras that need this
approach.

Regarding larger size screw heads, remember that both Tek and HP used
PoziDrive screw head fasteners. These are NOT Phillips even though they
look quite similar. The distinct advantage of PoziDriv is that the
driver does not cam out of the head as it does in a Phillips head.

But, if a Japanese product has what looks like a Phillips, remember that
it is more likely a JIS head. So, you need to have Phillips, PoziDriv
and JIS screw drivers in your tool kit. You really need the correct tool
for the job!

Larry


On 2/1/2021 11:46 AM, snapdiode via groups.io wrote:

They are typically 1/20" or 0.050" keys. Sometimes it's Bristol drive

but if someone forced a hex key in there it's probably not a Bristol drive
anymore.

Unfortunately I have found no way to extract a stuck set screw of that

size. You might try a 1.3mm key, sometimes they really are 1.3 and not 1.27
so you get a bit more grip. I don't know, seems random.
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)

On Feb 1, 2021, at 16:36, Paul Amaranth <paul@...> wrote:

These things rarely get seized; they are just really tight.

If you can heat the screw with a very small soldering iron and let it cool
(or shoot it with freeze spray), it might loosen up enough to get out.

Paul

On Mon, Feb 01, 2021 at 01:32:47PM -0800, Jeff Dutky wrote:
I have had success using a torx driver and angling it to wedge it in, applying a high down force along with the angling force, and turning very slowly so that it doesn't slip and further turn out the hex opening, or the bit on the torx driver. I had thought that I was ruining the torx driver, but it seems to have survived the ordeal relatively well. Still, it's best to use a sacrificial tool for this process.

-- Jeff Dutky

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows

They are typically 1/20" or 0.050" keys. Sometimes it's Bristol drive but if someone forced a hex key in there it's probably not a Bristol drive anymore.
Unfortunately I have found no way to extract a stuck set screw of that size. You might try a 1.3mm key, sometimes they really are 1.3 and not 1.27 so you get a bit more grip. I don't know, seems random.

I have had success using a torx driver and angling it to wedge it in, applying a high down force along with the angling force, and turning very slowly so that it doesn't slip and further turn out the hex opening, or the bit on the torx driver. I had thought that I was ruining the torx driver, but it seems to have survived the ordeal relatively well. Still, it's best to use a sacrificial tool for this process.

-- Jeff Dutky

Hi
When I find in that situation I use a torx drive, the size that best fits, it has always worked for me

-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de snapdiode via groups.io
Enviado el: lunes, 1 de febrero de 2021 20:47
Para: [email protected]
Asunto: Re: [TekScopes] Extracting a knob grubscrew

They are typically 1/20" or 0.050" keys. Sometimes it's Bristol drive but if someone forced a hex key in there it's probably not a Bristol drive anymore.

Unfortunately I have found no way to extract a stuck set screw of that size. You might try a 1.3mm key, sometimes they really are 1.3 and not 1.27 so you get a bit more grip. I don't know, seems random.







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