lab scope for automotive use

[puckhead]

i have a heathkit automotive ignition oscilloscope that works very well, nice steady display. its 60 yrs old, tubes. uses 4 pin amphenol connector to the pick ups. for the lab scope, i bought a hantek capacitive clamp on probe for the HV, and clamp on probe for a trigger signal. they are bnc. the problem is i can not get a steady , usable image on 3 different scopes. the trigger signal is steady, although the voltage peaks vary. the image from the HV pick up is jumpy, its not even on the horizontal. ive tried all sorts of trigger settings and levels. no change, and even auto trigger looks the same. id like to try the heathkit probes on the lab scope, and am working on making an interface, amphenol to bnc. i will do the same to use the new pick ups on the heathkit. i want to see what is what, maybe the new probes are just poorly made. that will take time to source the parts. in the mean time, maybe someone can see something im missing. this is a link to the trigger pick up :

this is the jumpy secondary pattern:

thanks

 

[rjenkinsgb]

The first one look fine, except you have not got the appropriate timebase "sync" setting on the scope to lock it laterally.

The second looks to be missing the ground, so it has random variations superimposed on the wanted signal?

 

[danadak]

Keep in mind the RPM is not fixed for starters. If you had a DSO you could use a qualified trigger,
\otherwise you are stuck pretty much with level based triggers in the Heathkit. That old a scope
might need alignment on trigger circuits, all the carbon comp R's in the scope have drifted over
many years, typically rising. I regularly see at much as 40 - 50% change. in gear I work on.

Regards, Dana.

 

[ClydeCrashKop]

Hantek HT25 Auto Ignition Probe $17.88​

https://www.amazon.com/Hantek-Ignition-Capacitive-Pickup-Probe/dp/B01B17VSH4

And for the primary side, Hantek HT201 20:1 Attenuator for Automotive Diagnosis, because it can reach 400 volts and your scope doesn’t want more than 200 volts.
https://www.amazon.com/Hantek-HT201-Oscilloscope-Attenuator-Diagnostics/dp/B07HJ6P1M5
Do you need a second Hantek HT25 to get a good trigger?

Good animated web pages for engine diagnosing. Scope patterns at the end.
https://www.zcar.com/threads/diagno...ark-plugs-scope-ignition.422423/#post-2785501

 

[puckhead]

the secondary pick up has a ground clip, maybe is poorly made. i'll look into that. thanks. to the second reply, i do have a DSO, and tried it with every type of trigger , all the patterns looked alike. please tell me more about qualified triggers, im not aware of that term.

thanks

 

[Nigel Goodwin]

That old a scope
might need alignment on trigger circuits, all the carbon comp R's in the scope have drifted over
many years, typically rising. I regularly see at much as 40 - 50% change. in gear I work on.

Only really true for valve based equipment (I don't know if the Heathkit is valve or not?), even then it's usually specific values (such as higher resistance ones) that tend to go even higher, and ones in specific locations (such as anode loads. Often they eventually go completely open-circuit.

 

[danadak]

My repair experience is plate and cathode R's exhibit greatest change, and grid and bias
usually 20%. Carbon comp.

I recently went thru a box of carbon comp and < 10% were in spec. Various wattages to boot.

Metal film, which I am prone to thinking they are perfect, are not -

https://eepower.com/resistor-guide/resistor-materials/metal-film-resistor/#

Heath is mostly discrete transistor. I am not aware of any equipment 20+ years or older that
do not need periodic alignment. Thats usually stipulated in equipment manuals and frequency
of alignment stated as well. Further discrete manufacturers, passive and active, usually have
supporting docs on component parametric change as well. Pretty much nothing in our business
stays constant forever.

With respect to trigger that tends to be relatively easy test to do. I have a number of Tek maniframes,
transistor and basic IC based, that need periodic cal. And of course the tube versions as well. Even
DSO's with their self cal routines regularly find out of spec issues in their signal path.

And lest we forget caps, like ceramics, electrolytics, silver micas all have numerous environmental
and T effects on long term stability.

I had a transistor Heath based dual trace and it got to the point it would not trigger on anything.
Some work on it restored it.

Regards, Dana.

 

[Tony Stewart]

Whatever probes you choose 10:1, 20:1, 100:1 the load cap must be matched by the same ratio as the scope input and calibrated. Don't use 1:1. and keep the ground clip short. Then you ought to get textbook square waves from a test signal.

 

[puckhead]

to be clear, the 60 yr old heathkit scope is working perfectly. the image is super steady, clear. i want to duplicate that on a bench scope. i bought special purpose pick up probe and trigger probe for this purpose. the videos are of a hitachi v-650 analog scope with the new probes. i also tried a tek DSO, same jumpy image. it maybe just be poor quality probes. the heathkit doesnt have bnc, so to try the heathkit probes on the hitachi, i have to build an interface. same to use try the new probes on the heathkit. i am in the process of sourcing connectors to do that, but posted the videos to see if i was just not set up correctly. the suggestion that the secondary capicitance pick up isnt grounding properly sounds possible. i dont use a scope everyday, but thinking about it, a poor or no ground does cause the horizontal to be all over the place.