In circuit testing of smd capacitors on Mac Pro logic board

[jimmyc_]

Hello chaps!
I’m looking for advice on incircuit testing of smd capacitors specifically on a Mac Pro logic board.

I’ve confirmed the fault is due to the Logic board. I’m not sure where the fault is, thought to start with testing the smd capacitors.

Advice?

[sean0118]

You can test if they are short circuit, but you probably won't get accurate ESR or capacitance readings while in circuit. Check the voltages / resistance to GND of all the power rails.

Check out Louis Rossmann's youtube if you haven't already.   

[jimmyc_]

Thanks!

[reyntjensm]

The logic board i way too complicated to start measuring every capacitor and have a chance to find a bad cap and solve the issue like that. What model do you have? What board type? How did the issue started? Check youtube/google with the board type number. I've fixed many macbook's by looking at the most common problems on those specific devices. If it's not water damage, you should be able to find your issue online.

[perieanuo]

the logical thing to do is track the voltage rails or like someone suggested, track usual problems on your pcb
i prefer always first one, is the thing to do
if you could get some schematic or some power rails voltages, start here then after identifying the voltage rail with problems, then atttack your regulators/capacitors or whatever
it's about learning also the right approach, not searching needles in haystacks. i repaired laptops intensively for almost 2 years at pcb level, never used a esr tester directly onboard, usually you got shorted caps, not degraded esr causing regulator to fail. usually ==  almost every time...
esr tester is good for smps repair (not in circuit) and for sorting your drawers or in r&d

[kripton2035]

this is fine to find shorted capacitors
http://kripton2035.free.fr/Projects/shorty-display.html

https://youtu.be/L4V3BWReZLY

[David Hess]

This is not what I would recommend but it is what I would do.

Assuming that the power supply is shutting down because of a shorted capacitor, I would use my own current limited low voltage power supply in its place to force a current through that supply rail, and then I would use a sensitive voltmeter to track the current, and/or search for a hot capacitor using temperature measurement.