• Please review our updated Terms and Rules here

Triggering Oscilloscope Externally Question

Tincanalley

Experienced Member
Joined
Aug 26, 2019
Messages
176
Location
Los Angeles, CA
I will be using my scope to work on a Tandon floppy drive using the SM as a guide. I'm not an expert when it comes to using a scope, but I've successfully used it for a number of projects. However, I've never had to externally trigger it like the SM requires for a couple procedures (two probes and an external trigger). I know my scope requires a BNC connected lead for this purpose, but I can't find any information about the required lead. Is it just a standard BNC to clip or grabber? If so, after I connect the red lead to the test point, so I need to connect the ground to the same point as the probes, or is this un-necessary as the probes are already connect to the ground point? I know my scope came with the cable, but I cannot find it, nor remember what the test end looked like, so I need to order one.

If it is of interest, I will be using a Tektronix 465. Not the newest of scopes, but it gets the job done.
 
Yep, it’s exactly the same probe as the Y channels of the oscilloscope.

I would always connect the ground points of each probe to a local 0V reference to where I am measuring the signal at.

Dave
 
I would always connect the ground points of each probe to a local 0V reference to where I am measuring the signal at

I sometimes use a silly arrangement where I clip one of those jumpers with micro-clips to a ground reference, and at the other end clip breadboard wires long enough to reach the ground clips on all my probes, so they’re all using the same common for sure.
 
Per my two videos at [here], I just use a normal probe for external triggering.
Couple questions.

In the video, no external trigger was connected. For that procedure, it notes TP7 for the trigger. How did you do it without an external trigger?

How will I do the track 0 procedure without a disk like the one called for in the SM? The disk has a track used to locate, I'm assuming, track zero based on the signal on track 0 of the disk? If that's the case, how do I locate track 0 of factory formatted disk?
 
Yep, it’s exactly the same probe as the Y channels of the oscilloscope.

I would always connect the ground points of each probe to a local 0V reference to where I am measuring the signal at.

Dave
So I should just get a 3rd probe and use that as the trigger?
 
I sometimes use a silly arrangement where I clip one of those jumpers with micro-clips to a ground reference, and at the other end clip breadboard wires long enough to reach the ground clips on all my probes, so they’re all using the same common for sure.
The SM points to specific test points for the ground. The ground TP is different for the alignment and track 0. If the test probes are grounded to TP10, shouldn't the trigger ground be as well?
 
Oh, and one last question....

I know an isolation transformer is used in many cases, but is it necessary here? I think that if this uses a no line voltage outside of the PS, and my outlets are wired correctly, it should be fine? I know when I did my TV, I was told that as long as the TV used an internal transformer, I didn't need an isolation transformer. I managed to scope the crap out of the entire set without an issue, so I'm assuming that info was correct or I just got lucky.
 
Yeah, I guess I have another question.... Since this isn't modern piece of tech, is it okay to pigtail the ground test point as I will never be able to get 3 clips on it. I know it is important to keep the ground as short as possible. I have a 10" wire with alligator clips on each end. So that would give me a total of about 14" ground wire.
 
The oscilloscope 0V/GND reference is connected to mains earth on all modern devices for safety.

Some old TV sets had either a live or neutral connected chassis, not mains earth. If this is the case, you could short circuit mains live to mains earth - bang...

Dave
 
Yeah, I guess I have another question.... Since this isn't modern piece of tech, is it okay to pigtail the ground test point as I will never be able to get 3 clips on it. I know it is important to keep the ground as short as possible. I have a 10" wire with alligator clips on each end. So that would give me a total of about 14" ground wire.
This is essentially what I described in terms of extending the ground so all the clips can reach it. So in my experience it’s fine. Obviously keeping things as compact as possible to minimize noise is good, but I’ll hazard the guess that for aligning a floppy drive the frequencies aren’t going to be high enough to worry that much.

(I’ve used this daisy chained ground mess to troubleshoot NTSC video output circuitry with a 12mhz pixel clock and it’s been fine.)
 
This is essentially what I described in terms of extending the ground so all the clips can reach it. So in my experience it’s fine. Obviously keeping things as compact as possible to minimize noise is good, but I’ll hazard the guess that for aligning a floppy drive the frequencies aren’t going to be high enough to worry that much.

(I’ve used this daisy chained ground mess to troubleshoot NTSC video output circuitry with a 12mhz pixel clock and it’s been fine.)
Sounds good. Hopefully I be able to start tomorrow when the third probe (for trigger) arrives. Going to be a big mess as I need to clear off an area for the machine, scope, monitor and drive hanging outside the machine running it. Should be fun.
 
Per my two videos at [here], I just use a normal probe for external triggering.
In the video, no external trigger was connected. For that procedure, it notes TP7 for the trigger. How did you do it without an external trigger?
There are external triggers being used.

In the CS-2110 video, the third probe is connected to the BNC connector labelled 'CH3 or A EXT. TRIG', with the A sweep trigger source switch set to one ('1/1' or '1/10') of the two settings that use the aforementioned BNC connector as the source.

In the ADS1102CMl video, the third probe is connected to the BNC connector labelled 'EXT TRIG', and in the unseen trigger menu, the source will have been set to 'Ext'.

How will I do the track 0 procedure without a disk like the one called for in the SM? The disk has a track used to locate, I'm assuming, track zero based on the signal on track 0 of the disk? If that's the case, how do I locate track 0 of factory formatted disk?
So, no alignment floppy. Maybe the procedure at [here] helps.
 
There are external triggers being used.

In the CS-2110 video, the third probe is connected to the BNC connector labelled 'CH3 or A EXT. TRIG', with the A sweep trigger source switch set to one ('1/1' or '1/10') of the two settings that use the aforementioned BNC connector as the source.

In the ADS1102CMl video, the third probe is connected to the BNC connector labelled 'EXT TRIG', and in the unseen trigger menu, the source will have been set to 'Ext'.


So, no alignment floppy. Maybe the procedure at [here] helps.
Ah, got it. The link only had one 11sec video and I only looked at the trigger BNC connection. I just looked again and see the CH3 connection.

I looked over that procedure and it is for aligning to the tracks. The last part notes how to verify you are on the correct tracks, but nothing about what to do if you aren't. The drive I am working on is 2 tracks off it seem from zero. If I start on zero, it has a ? for track. It isn't until I move it up 2 steps that it shows 0 for the track number.
 
Back
Top