Re: more scope questions
- From: "Phil S." <psymonds@xxxxxxxxxxx>
- Date: Sun, 17 May 2009 18:15:03 -0400
...in between...more pictures to look at, too.
http://home.comcast.net/~psymonds/BK1472.htm
"Benj" <bjacoby@xxxxxxxxxxx> wrote in message
news:adc396b5-1b0f-467a-9071-28a1e4d9f718@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On May 15, 10:54 am, "Phil S." <psymo...@xxxxxxxxxxx> wrote:
So, the saga continues....
I was able to easily put together a 2-gang pot 1KB front and 5KB rear. I
didn't understand which part provides the resistance -- it's the ring on
the
bit of tan board with the solder terminals. It was simply a matter of
taking the back half of the 5K pot and transplanting/adding it to the 1K
pot
and voila! Installed and working properly. Actually, a rather simple
job.
I now have a working vertical position control on Ch A and can see a
signal.
This is not to say the scope is working.
Does Channel B work as well? I haven't been following this saga except
at the very first.
A and B work about the same.
Lets start at the beginning: Pull the trigger knob that says pull for
auto. That is supposed to get a horizontal line on the screen. Set
Each channel to AC and v/cm to 1.
You should be able to move trace up and down screen using position
controls for each channel if it's Ok.
Up and down work.
Here's the front panel:http://home.comcast.net/~psymonds/BK1472.htm
Afterwards, I did see some activity on the scope, but nothing I would
call a
waveform. There is only trace display up to the vertical line one to the
right of center, so 40% of the display is blank. Rotating the horizontal
control makes it worse, not better, because it moves the display further
to
the left. I would actually be very happy to get a signal across 60% of
the
screen, if it were a good signal. Any comments on what I might do to get
100% of the screen in use?
Try pulling out the horizontal position knob (see where it says pull
for 5X mag?) That will give the knob more range!
You'll have to actually get a trace to see if it's a DC centering
problem or a horizontal amp problem.
5x makes it run together. Seems too fast.
I found a very nice 9 min crash course on using a scope on YouTube. I'm
reasonably clear about what the various controls do.
Good start. ONCE you get a line on the screen you can play with
brightness and focus and astig to make the line as fine as possible it
should be a nice line if all that is working. These controls interacts
so just play around a bit.
These work.
My questions have to
do with actually getting the scope to show a trace. I have one Tek 10x
100mHz probe. I don't know if the probe is actually OK. It came with
the
broken Tek scope that I sole. First question: is there a way to know if
the
probe is OK?
Yes, but forget the probe now. Just use wires to connect things.
Connect that 1 volt peak to peak calibrator to the input of both
channels. Set V/cm to 1v/cm. Then set the sweep to about 50 ms. You
should see the "line" on the scope fatten to about one division wide
if the channel is working. Try both channels (chosing with "mode"
control). the display if you are lucky could be a nice square wave.
Otherwise it could be a fat blur. If it's still a thin line, that's
bad news. If you flip the input from AC to gnd it should go from fat
to thin line (signal to no signal ...grounded out).
I'm having difficulty fattening it. I think maybe I'm not doing it right.
Will play with it more as time permits.
A very simple way to test each channel for signal is to poke a bare
wire into the center of the input BNC connectors. Now up the setting
on v/cm to .1 or less. Take your finger and touch the wire in the BNC.
If the channel is working you should see the line fatten wide or maybe
even see a 60 hz trace.
Both channels show a trace, though not very tidy looking. I think "fuzzy"
is the right description. I tried to photograph it without success. I am
convinced it is a sine wave trace...to the middle of the screen.
There is a calibration port (NE corner) marked with a sq wave symbol 1V
P-P.
I take this to mean it will provide 1V, but how would you set the v/cm
and
the sweep/cm to get it to display? Is there some other some other easy
signal source that I can rig up?
If the "calibrator" is working it's there to BE the "easy" way, OK?
If there is no output from the calibrator (an ordinary ac voltmeter of
the cheap kind should show AC volts there between the terminal and the
ground on the scope input.
Please don't think I'm silly here...can I put the probe to the hot side
of
the AC line signal to get a 60Hz wave? With a 10x probe, this means the
scope sees 12V?
Don't Do IT! There is a question about the voltage ratings of
probes. The probe is not for your scope in the first place. and it's
10 x to increase speed your scope doesn't have anyway. I told you to
forget it! OK? If you want to do a low test voltage use an old
filament transformer at 6.3 volts AC. It's isolated from the line and
low enough not to damage things. But do that ONLY if the calibrator is
dead!
I've got an old laptop that I can charge up. Should I find some freeware
that will run on a computer? Do I just stick the probe in the sound
output
port?
Use the calibrator, dammit! It's what it's FOR!
The calibrator...the Fluke reports 0.58v. No freq measure on the Fluke, an
old bench model. The Tripplett says it's ~1KHz and .48v
If you can't get the trace left report back for more answers. It may
be a bad horizontal amp (as someone noted "half of it blown) If you
can't get anything through either channel to make a fatter fuzzy
trace, report back. With two channels it's likely one should be
working.
IF you get a fat trace but it's fuzzy and not a square wave, then
start with the horizontal triggering. First try twiddling the trigger
level. If that doesn't work move source to Chan A and twiddle. IF all
else fails run a wire from the calibrator into the external binding
post. and switch to "ext" trigger and twiddle. If you can't get trace
to lock with all that this is not good. Means trigger circuit is bad.
I believe I've got it triggering OK. I will have to fiddle more to see if I
can get a sq wave.
But right now your first order of business is to forget the 10 x probe
and build yourself a pair of 1x probes! This is done with a length of
cable with BNC connectors on both ends. Cut it in the middle and
solder two small alligator clips on to each length at the cut. One
clip goes to the center wire. the other on a short wire soldered to
the shield of the cable.
We'll deal with the 10x probe once you get a trace going!
Get busy!
I'm pretty sure Steve is right about the power rail, and I'm not surprised.
He seems to have the mojo for this sort of thing. Horizontal is dead on the
right side.
The darn tube has a shield over it. I can't see the tube number and think
it is probably unwise to attempt to dismantle it just to see. The tube
socket has 3 blue wires, two white wires, 5 fat red wires, and one thin red
wire. I was hoping it would be obvious what's what. Also, the PT is in a
place where I can't really see what's what without dismounting it, though it
runs into a board, as do the wires to the tube. So, I think maybe I'm
reduced to poking around, but am relatively clueless. The high voltage
board is in the back and awkward to access, as there is a shield over the
trace side of it and other goodies in the way on the tan side.
I feel so close, yet so far.
.
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