Any oscilloscope experts?

[b3lha]

I picked up an old oscilloscope recently and as I was doing some other work on the SVX tonight, I thought I would have a play with it. I understand how to operate the volts/div and secs/div, but I'm a bit fuzzy on the other knobs and buttons.

The only easily accessible wire that carries signal is the front fuel injector on the driver's side. So I stuck a pin through the wire and hooked up the scope. It was my understanding that this wire floats and the ECU pulls the it down to ground in order to pulse the injector. So I expected to see the voltage floating around 12v and dipping down to zero about 6 times a second (at idle rpm).

But all I am seeing is a straight 12v line with a little bit of noise. I tried changing the timebase, twiddled all the knobs that I understand, and a couple of the ones I don't. But still couldn't get anything different. I revved the engine to try and get longer pulses. I even tried the other wire on the same injector, just in case, and got the same thing.

Any idea what I could be doing wrong? I keep thinking it must be something to do with triggering. Unless I can get the scope to keep each pulse in the same place on the screen then it will be over before I see it?

If nobody has any better ideas then I'll for oscilloscope tutorials.

[crazyhorse]

You could probably the make/model and get the operator's manual.

Barring that, here's the one I like.
https://www.cs.tcd.ie/courses/baict/bac/jf/labs/scope/

[Trevor]

Greetings Phil,

Have you established that it is working OK. Will it pick up an induced 50 cycle signal from the mains 230/250 ac supply, i.e. using a simple unshielded wire within a short distance of mains wiring.

There are books covering the use of oscilloscopes and possibly something on the net. I will have a quick look.

Special regards, Trevor.

P.S. Try these ----

http://www.doctronics.co.uk/scope.htm

http://www.facstaff.bucknell.edu/mas...pe/Scope1.html

http://www.radio-electronics.com/inf...cope-scope.php

[Dessertrunner]

Phil Most of the time I haven't picked up signal it could be for the following reason,

• Wrong voltage type AC or DC.
• Wrong signal source or trigger, not quite sure exactly but its not a simple as a rising or dropping wave trigger it also has to do with base voltage.
• Timing or catching the signal at the right cycle.
• Wrong height gradent. Its possiable that the spike you see just need to be increase by the correct amplatude.

You can do a simple test on a battery or a DC power source and touch the lead trigger wire to see if the scope works correct first. By the way when you get it going its interesting to look at the Knock sensor.
Tony

[LetItSnow]

I was able to pick up the ignition signal in my Legacy... I'll try to help. What's the brand and model? Can you get us a pic of the knobs?

[Dessertrunner]

Phil I just tried and didn't get it either. I think that my mistake was to assume that the trigger was postive so the other lead was on the earth. I think that is wrong. It got dark so I will try later, it may be that the trigger is a negitive voltage so other lead goes on the postive.
Tony

[Dessertrunner]

Got a reading its the "Y" input on the scope, probe on the black & white injector wire & other lead to earth on car. Then set timing etc.

[Suby Fan]

does your occiliscope go to 5-10 milliseconds?

[b3lha]

Thanks for the help and advice guys. I think I have it working now.

The scope is a Telequipment D83 made in 1976. I downloaded the manual for it from the "Boat Anchor Manuals" website. Oscilloscope manuals are funny things. One sentence to describe each knob and then pages of schematics showing the inner workings together with the precise specification of every single transistor, resistor, capacitor and other component on the board.

I got it to work by grounding the scope to the + terminal of the car battery, setting it for negative triggering and then connecting the probe to the black and white wire like Tony said. When I say probe, I mean a bit of old coax network cable with a crocodile clip soldered to the end.

In the first photo, the scope is set to 5 volts/div vertically and 0.1 second/div horizontally. You can see a -12v pulse every 0.2 seconds. That means the injector is pulsing 5 times per second which means the crank is rotating 10 times per second = 600rpm, which sounds about right for idling speed.

In the second photo, the timebase is zoomed in to 2 milliseconds/div, showing that each pulse lasted for 3 milliseconds.

Success! Time for a beer to celebrate.

[Dessertrunner]

Great work. I think the best thing about scopes is to look at the singal from the various pulse types sensor Knock, Cam & Crank. If the curve is not clean you know the sensor is failing.
I want to build a harness to plug between the car and the engine so I can pick up a number of test points to be able to use the scope more often and pick up problems before the the CE.
Tony

[Trevor]

Good one Phil, you are flying.

You should not have to worry about a probe for the measurements you will be involved with.

I wish you all the very best with your quite extensive and taxing project.

Going to open a home brew right now and will drink to you. Have a happy Easter.

Cheers, Trevor.