Oscilloscope troubleshooting

Frank Miller

Frank Miller

Well-known member
Back in the 80s a friend had a garage with one of these and it seemed handy to get a good evaluation on the engine ignition system. I never see anything about these and was wondering if anyone here ever used them to troubleshoot flathead ignitions.
 
They work very well to check out the wave action of the ignition system to verify proper function of all components. Now days a person can purchase a program to use a lap top computer as a digital electronic oscilloscope. The old ones are still out there but they are a lot larger and heavier that a light digital portable model.
 
Yep. For less than a $100, dedicated handhelds the size of multimeters are available these days to help you get your flathead up & running again.


487062
 

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When i worked for the cadillac dealer we had a Allen scope i always was the one for engine misfire because i understood the machine spent a lot of time training on it you could pick out a spark plug misfire a bad ign. wire you could short out any cyl. watch the drop of the tack you could adj.the screen to different patterns to much to mention at the Chrysler dealership we had a sun machine that worked quite well but i’d take the Allen over it those were the good old days
 
I have one of these DSO138’s I paid $12 bucks for it a while back so I could learn about scopes. I hope someone will chime in on how to use it exactly to diagnose flathead ignitions.
 

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will an Oscilloscope diagnose a bad capacitor? I had one causing a random flutter at idle and would just cut off at idle like you turned the switch off. After checking connections, voltage, and changing the coil, I changed the capacitor and cured it.
 
>>>will an Oscilloscope diagnose a bad capacitor?>>>After checking connections, voltage, and changing the coil, I changed the capacitor and cured it. .>>>


Maybe. Maybe not. Easier to check connectiions, voltage, change the coil and capacitor. Then see what happens. Oh! You already did that. Good job! 8^)
 
40cpe said:
will an Oscilloscope diagnose a bad capacitor? I had one causing a random flutter at idle and would just cut off at idle like you turned the switch off. After checking connections, voltage, and changing the coil, I changed the capacitor and cured it.
Click to expand...


Probably not in a literal sense but you'll probably see some stray voltage or odd spikes that will make you look in that direction.
 
After making a living working for Allen Textproducts and sun equipment for many years . The subject is way too deep to even start ! Yes a scope can analyze the flathead and has for many years . I guess the best i can do is simply answer any questions that comes fro this thread .
Ask away and i will try to address the concern ??????
 
>>>Repeat>>>under a competent operator>>>


That's different. Not a repeat. For an incompetent oscilloscopist such as myself, I repeat that it's easier to check connections, voltage, change the coil and capacitor. Maybe look at the points too. 8^)
 
40cpe said:
Repeat: Will an Oscilloscope under a competent operator diagnose a bad capacitor ?
Click to expand...


Yes. The scope will show oscillations from the condenser discharging. If those oscillations are missing, too short, or uneven, the condenser is a likely suspect.



Terry
 
I can't tell what's being compared in those two patterns. One pattern seems to be for the secondary hipot circuit, the other for the lopot primary circuit. Normal spark is referred to in both?
 
Jack E/NJ said:
I can't tell what's being compared in those two patterns. One pattern seems to be for the secondary hipot circuit, the other for the lopot primary circuit. Normal spark is referred to in both?
Click to expand...

Good question. I agree with you, how can say normal spark occurs on a pattern for a bad condenser??? Reference to event "B" should read, this is where the normal spark would occur if it didn't have a bad condenser. On a scope for those who have never played with one, vertical lines represent the amount of voltage generated, and the horizontal lines are the time between the events.

What you don't see in those previous patterns is the coil saturation dwell time, that long horizontal line between when the points close and current begins to build up in the coils' primary winding until it stops flowing when the points open at the firing line.

You normally see that long dwell time in the secondary waveform. A defective condenser would interfere with the current flow through the points and the primary windings and you can see that in the previous patterns, the coil's primary current is not flowing long enough, it abruptly stops as the point close. Without that dwell time the coils' primary winding cannot build up a large enough magnetic field and when the points open and the magnetic field collapses it will not be strong enough to generate a strong magnetic field in the secondary windings, which means a very weak spark or none at all. I guess it shows up as a lightly different pattern on the primary wave form too. It has been 30 years since I messed with this stuff daily.

Its hard to find good images. This image is an electronic ignition you can tell by the current limiting hump from the transistorized ignition. A points ignition pattern would look the same except without that hump in the points closed dwell line. On the previous patterns the points close (up and down oscillations) is right up against the firing line. What I don't understand is why there would be a vertical firing line and a horizontal plug burn time at all in those previous patterns if the condenser was defective?
 

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