Leader lbo 508 oscilloscope help

[eccerr0r]

Re: Leader lbo 508 oscilloscope help

Get rid of the gypsy capacitor meter, it is being fooled by high leakage current. You did measure leakage current or ohms at least on the caps?

Incidentally my Sencore IIRC also gives higher cap ratings for leaky capacitors. However it does have one saving grace : it has a leakage analyzer so you can also test for that condition...

ahhhh my Sencore is a gypsy!

[Dannyx]

Re: Leader lbo 508 oscilloscope help

Ok, so after a LONG time, it was finally my turn: just me and the scope to mess with ....Never having used a scope before, let alone one which we have no idea if it's functional or not, I just realized I have no idea how to use this thing....I just push buttons
The reason I NEEDED to use it this time is because I want to measure if the SG3525 IC in the picture outputs anything. It's out of a large DELL UPS and controls 6 FETs that boost the battery voltage (Dell 2700w j728n which I'll probably write a separate post about). It also seems like the perfect IC to try a scope on, but it's just a flat line when I probe pins 11 and 14 - not even noise or anything, so I realised I may be doing it wrong, since it's not as easy as it seems, especially with an old scope like this. Ignore the wires soldered to the riser - they were soldered by my colleague so he could measure different points while the riser was mounted to the UPS since there's no room for probing in there...

The BNC connector for the probe ITSELF has a trimmer inside it and a switch for 1x 10x and REF on the probe itself. I just grabbed it from my colleague as it is and left it as such. There's a switch for AC/GND/DC on the scope itself (pictured) which I THINK is for what's called "coupling". It's set to AC currently.

So the first order of business is to make the scope function properly and then we move on to the SG IC which could very well be flat-lining because I don't know how to use the scope and not because there's something wrong with it. True, it was tested out of circuit on its little riser, with just VCC present, but REF is there on pin 16, so we can ASSUME the outputs should be switching as well, but I get nothing at all.

Another indication that I may be doing it wrong OR the scope is not functioning as it should is that the hook on the front of the scope which says "CAL 0.5v p-p" doesn't cause a nice square wave pattern to form on the screen, no matter how much I go all twisty with the knobs, so there's some unknown elements here Practice, practice, practice...

[stj]

Re: Leader lbo 508 oscilloscope help

dc coupling,
vertical-mode to ch-1

[Dannyx]

Re: Leader lbo 508 oscilloscope help

If I may, should that be channel 2 since that's where I had my probe plugged into.

I eventually got it: shutdown pin 10 was not grounded and was being held at 5v due to a pull-up resistor, so the IC wasn't operating. I eventually did get some waveforms, but I'm not sure how to interpret them - tough with no actual values displayed on the screen about what those peaks and valleys represent. Adding to the issue is that the scope seems to be out of whack and not "sensitive" enough - had to turn that VOLTS/CM knob I pictured all the way CW to .01 to get anything to display. From what I understand, that knob sets how many volts a single vertical division represents, so if set to 1 and I hit the probe with 1v, it should deflect up by one space ?

There's also the matter of the switch on the probe itself: not having anything to lose or break, since I powered that riser from a SLA battery, completely isolated, I messed with it to see what it does. From what I remember in one of my reads, it is an impedance switch which toggles between a factor of 1 and a factor of 10 relative to the scope's own impedance which I THINK should be 1Mohm in most cases...not sure what the REF position does.

Think there may be something wrong in the amp section that causes the sensitivity to be too low and react only when the V/DIV is all the way up (or "down", really). To test, I cranked it CCW to 10v and touched the probe directly to the SLA battery expecting to see it move by a little over one division. Not sure if this was a good idea now that I think of it, but like I said: no dangers either, at least I don't think so since the input says 600v peak-peak which this SLA clearly ain't I'm aware DC is not what a scope is for, another reason why this may have been a stupid experiment to begin with...don't judge - I'm as new as it gets to a scope !

[stj]

Re: Leader lbo 508 oscilloscope help

yes, volts-per-division,
but remember if your using a divider in the probe (x10) then you need to take that into account.

[Dannyx]

Re: Leader lbo 508 oscilloscope help

At 1x, the signal is "stronger" indeed....which makes sense now that I think about it, but can cause issue with sensitive circuits.