Scope probe ground clip sparking on chassis

[Bob Parker]

Re: Scope probe ground clip sparking on chassis

I'm not going to follow this thread any more, while I still have some hair.

Just be very careful where mains voltages are concerned because the old saying is very true: "A little knowledge is a dangerous thing."

[Toasty]

Re: Scope probe ground clip sparking on chassis

Was this ever resolved?

[Agent24]

Re: Scope probe ground clip sparking on chassis

Gave up on it for the time being. I think the tuner is pretty screwed anyway. Even if it's something simple like corrupt firmware I don't know where I'd get a new copy.

Might give it some more time.. sometime... if I can be bothered.

[riotpack]

Re: Scope probe ground clip sparking on chassis

http://www.questronix.com.au/info/info_tingles.htm

Read that.

[Dranoweb]

Re: Scope probe ground clip sparking on chassis

I apologize for digging up a really old post
I would also like to say thanks for the manual - I just inherited a q1280 myself.

just wondering what frequency probe you went with.

I had high hopes of using this at 470mhz, but looking at the 100khz on the front, i think it's just going to do for my switch mode testing etc.

again sorry for the old post revival - but info on old stuff, is usually in old posts - and indexed on google.

[japlytic]

Re: Scope probe ground clip sparking on chassis

From Kemet.com:
X capacitors are across the line. { Think X = cross }
If they short-circuit, the risk is fire.

Many X-class capacitors are flameproof, a condition of agency approval.

Y capacitors are from line to chassis. { Think Y = upper points are power lines, lower is ground. }
If they short-circuit, the risk is a shock to the user. => as is your case

Y-class units are designed not to fail, but when the do fail, they fail safely (go open circuit); again, a condition of agency approval.

---

Remember capacitors are reactive components as well (their reactance is dependent on frequency), which means Y-class capacitors can transfer minute amounts of current between the line and isolated chassis, but this is not enough to become dangerous.

[Agent24]

Re: Scope probe ground clip sparking on chassis

just wondering what frequency probe you went with.

I had high hopes of using this at 470mhz, but looking at the 100khz on the front, i think it's just going to do for my switch mode testing etc.

I got a cheap 50 MHz probe on eBay from some Chinese seller. Probably doesn't even work up to 50 MHz but I doubt it matters since that scope is only good for 5 MHz anyway.

The most limiting issue with this Q1280 is that the controls are unmarked and uncalibrated. You have no way of knowing voltage and frequency accurately unless you compare to a known signal.

Despite that though, it's still useful, and much better than no scope at all. But if you can afford it you should probably get something better.

[redwire]

Re: Scope probe ground clip sparking on chassis

I've repaired a few scopes that got damaged when a noob connected the probe to a mains-referenced circuit. Like a TV or SMPS, the -ve DC rail is live and big spark when you connect the scope probe ground there.
It melts a (chassis/earth) ground trace in the scope and it becomes a floater. The X-cap then bites you. Hard to find the pcb break, but most scopes have their bnc gnd to the power cord, if you check with an ohmmeter. They're not designed for a 15A fault there.

[redwire]

Re: Scope probe ground clip sparking on chassis

Oops I meant the Y-cap bites you, its leakage current can make small sparks or give you a jolt because the scope lost its ground trace.