intrigued, i put the DMM in continuity test and to my horror i find that the input "outer rim" of the BNC connector is part of the chassis which is GROUNDED to mains ground!, WHAAAA, FAIL! which essentially grounded the neg output of the bridge rectifier(-150Vdc~) when i touched it, aren't CRO inputs supposed to be fully floating?.
or i need an esoteric differential probe?
so how do i go about testing this? if i can't ground it....
you could run the scope off an inverter ? others will know more on this. Your other option is use both channels and not the earths making one channel "earth" and the other signal, then use the subtraction feature of the scope to give you the difference and voila'
aren't CRO inputs supposed to be fully floating?.
About isolation transformers(which i don't have...): is it a simple 1:1 transformer? Dave/Janne, how would it prevent the issue, even if it's isolated the neg input is still at -150V from ground, or because it's across the transformer it doesn't matters?
you could run the scope off an inverter ? others will know more on this. Your other option is use both channels and not the earths making one channel "earth" and the other signal, then use the subtraction feature of the scope to give you the difference and voila'I like this idea, never crossed my mind, but i'm not sure if this CRO has X/Y substraction capability, i'm gonna check now.....
my other gross error was not using the lamp-series we have for this(TWICE!), that would have prevented the fireworks....
About isolation transformers(which i don't have...): is it a simple 1:1 transformer? Dave/Janne, how would it prevent the issue, even if it's isolated the neg input is still at -150V from ground, or because it's across the transformer it doesn't matters?
hehe, a simple visual inspection would have reveled the connectors are grounded, i simply never came across this situation before(always used a DMM to check main cap voltage), since this smps is behaving bad(that's why it's here) with low-freq 1.5V oscillations with triangular peaks in them(that don't show as variations on the DMMs i have) i was thinking about dry main cap..., and this happened...
Neilm, interesting device, floating AND isolated to eachother!
you could run the scope off an inverter ? others will know more on this. Your other option is use both channels and not the earths making one channel "earth" and the other signal, then use the subtraction feature of the scope to give you the difference and voila'I like this idea, never crossed my mind, but i'm not sure if this CRO has X/Y substraction capability, i'm gonna check now.....
my other gross error was not using the lamp-series we have for this(TWICE!), that would have prevented the fireworks....
About isolation transformers(which i don't have...): is it a simple 1:1 transformer? Dave/Janne, how would it prevent the issue, even if it's isolated the neg input is still at -150V from ground, or because it's across the transformer it doesn't matters?
hehe, a simple visual inspection would have reveled the connectors are grounded, i simply never came across this situation before(always used a DMM to check main cap voltage), since this smps is behaving bad(that's why it's here) with low-freq 1.5V oscillations with triangular peaks in them(that don't show as variations on the DMMs i have) i was thinking about dry main cap..., and this happened...
Neilm, interesting device, floating AND isolated to eachother!
intrigued, i put the DMM in continuity test and to my horror i find that the input "outer rim" of the BNC connector is part of the chassis which is GROUNDED to mains ground!, WHAAAA, FAIL! which essentially grounded the neg output of the bridge rectifier(-150Vdc~) when i touched it, aren't CRO inputs supposed to be fully floating?.
I know connecting the chassis of old equipment to the mains was common, but why were they doing it in the first place? Simplify wiring?
Makes sense. How did they isolate the aerial socket? Some high frequency 1:1 tranformer?
you could run the scope off an inverter ? others will know more on this. Your other option is use both channels and not the earths making one channel "earth" and the other signal, then use the subtraction feature of the scope to give you the difference and voila'
you could run the scope off an inverter ? others will know more on this. Your other option is use both channels and not the earths making one channel "earth" and the other signal, then use the subtraction feature of the scope to give you the difference and voila'
Hi,
I am wondering how this type of advice get past the moderators ?
This is AC mains you guys are playing with, for goodness sake ! Go to a technical college and pay for professional training if you do not know what you are doing. It might be 'cool' to blow things up but being electrocuted or severely burnt is not. Not to mention the potential damage to expensive test equipment.
Beginners reading this type of advice may sadly think it is correct because it is published on a well-respected Engineering blog.
Regards.
The moderators of this board and usually any board are not supposed to be experts, usually they are some of the more active members that "know the forum" and are around more to deal with spam and other trouble and of course are deemed to be gifted with sufficient common sense to keep things on an even keel.
I mean after 3 posts you must be an expert !
That aside welcome to the forum