Practicing my Osc skills advice

[Steve]

Hi guys,

I'm gonna be re-capping some Atari PSU's over the next few days and thought it might be a good opportunity to try and get before/after results like Exxos did in his PSU research. Could anyone recommend the basics to me like basic probe placements and settings to have the Oscilloscope on.

Ie; would you scope the voltage directly while it is powering an ST or using load resistors. Does it make a difference where you probe etc.

Cheers

[Steve]

I've been watching EEvblog to make sure I don't make any silly mistakes. Been quite a few years since I was at college using oscilloscopes

[exxos]

I think dave did a review of our scope..

ah just screw around with it.. probe the 8Mhz clock and fiddle and learn what all the buttons do.. or just press AUTO and not bother like me

[Steve]

Okay just hooked it up like this as shown in photo. Made sure to move away and isolate the 12v line with capton tape just to be extra safe. Having my probe on 10x does this reading show about 100mv of noise? Because it's about half a square of 20mv x10? Just learning how to read these again

PXL_20210213_113506991.jpg (381.46 KiB) Viewed 3472 times

PXL_20210213_113516207.jpg (297.03 KiB) Viewed 3472 times

[exxos]

Theres a setting in the scope to change to x10 probe somewhere.. so you dont have to translate voltages..

[Steve]

Found it Chris cheers
As a reference, this is my SR-98 I use for testing. It is fully recapped already and shows very good regulation and about 50mv of noise:

PXL_20210213_124726951.jpg (316.02 KiB) Viewed 3458 times

Here is the first PSU I'm servicing today.. DSP 508a... holy smokes! It fluctuates massively and doesn't even output 5v. Fluctuates between 2.7v and 3.4v.. crazy :

PXL_20210213_125042668.jpg (296.54 KiB) Viewed 3458 times

[mst]

Found it Chris cheers
As a reference, this is my SR-98 I use for testing. It is fully recapped already and shows very good regulation and about 50mv of noise:
PXL_20210213_124726951.jpg

Here is the first PSU I'm servicing today.. DSP 508a... holy smokes! It fluctuates massively and doesn't even output 5v. Fluctuates between 2.7v and 3.4v.. crazy :
PXL_20210213_125042668.jpg

First one is very good, 50 mv on a 5 volts signal is more than ok!

Second one is completely bad, it appears that the self regulated switching rate of the PSU doesn´t work properly.

[exxos]

First image looks OK.. If you use reduce the time base, maybe 500ns you should see a sine wave which is the ripple...

Your second image looks like part of the ripple.. If you increase the time you may see it better...your on 200mv as well... Try 50 mv like your first image..

In the measure menu, you can show volts min and max on screen..

[rubber_jonnie]

Theres a setting in the scope to change to x10 probe somewhere.. so you dont have to translate voltages..

Agreed, mine has a 10x switch on the probes, but if you forget to adjust the settings in the menus, it can really fool you. Most of the time I find 1x more than good enough on my scope.

Been caught out a couple of times too by accidentally knocking the switch to 10x and not noticing.