Things not to do with a multimeter?

[Sofian75]

I started to learn laptop repair a few weeks ago, since then I ve ordered several dead laptops to try to fix them and learn.
I fixed some of them and some I ve made things worse by blowing components.
Every time while taking measurements with my multimeter.

Yesterday I was working on a dell laptop motherboard, I was checking the charge IC for short in diode mode and it killed the chip.

So my question is are there things I should not do with my multimeter?
Or measurements I should do only with the charger and battery unplugged?

[stj]

try not to use the current mode,
use sharp fine probes - not the ones that come with them that can short pins together,
know the meter output voltage in diode/resistance mode and try not to use it on 1.8v circuits.
because it's usually between 3 and 4v coming out of the meter!

[stj]

as your in france, is there any french sites for test equipment manuals?
i'm looking for stuff for Metrix scopes!
i suspect there is a lot of these in france - maybe in government/military use because it's a french company.
so maybe some manuals are achived?

[harp]

Yesterday I was working on a dell laptop motherboard, I was checking the charge IC for short in diode mode and it killed the chip.

Interesting... can you describe what model of ic is it, what you do to destroy it, and how you notice fault and check it that measurement is cause fauly?

So my question is are there things I should not do with my multimeter?
Or measurements I should do only with the charger and battery unplugged?

Generaly avoid current measurements, and position in uA, mA and A scale and lead socket, except if you are absolutely sure what you are doing, and need to do this way. In this current mode, leads are like shorted, and measurement is used while device is power up, so everithing you touched is potencialy dangerous for your multimetar/device.

All measurement are done by unpluged all power source, mains, battery, bios battery, and discharged caps, except measurement of current, voltage, and frequency.
Temperature sensor also isolate with kapton tape or liquid solution like nail farbe or calafonium, because your device is powered during your sensor touching legs and ic...

[Sofian75]

Interesting... can you describe what model of ic is it, what you do to destroy it, and how you notice fault and check it that measurement is cause fauly?



Generaly avoid current measurements, and position in uA, mA and A scale and lead socket, except if you are absolutely sure what you are doing, and need to do this way. In this current mode, leads are like shorted, and measurement is used while device is power up, so everithing you touched is potencialy dangerous for your multimetar/device.

All measurement are done by unpluged all power source, mains, battery, bios battery, and discharged caps, except measurement of current, voltage, and frequency.
Temperature sensor also isolate with kapton tape or liquid solution like nail farbe or calafonium, because your device is powered during your sensor touching legs and ic...

It was the BQ chip.

Happened today again, this time I am pretty it's caused by the diode mode of my multimeter while the charger is plugged in.
Is something wrong with my multimeter or is it part of the things we are not supposed to do?

[redwire]

What make/model multimeter? They are not all the same.
More likely ESD or stray voltage hit with the charger Y-cap. Is this a cheap chinese charger?

[Sofian75]

What make/model multimeter? They are not all the same.
More likely ESD or stray voltage hit with the charger Y-cap. Is this a cheap chinese charger?

ZT102A from Aliexpress (free shipping)

I ve been using the diode mode on other boards for days without any problem, this time I forgot to unplug the charger so I am confident this is the source of my problems.

More likely ESD or stray voltage hit with the charger Y-cap

I am a beginner, can you translate please?

[stj]

nice meter - i have the regular screen version
https://zotektools.com/products/zt-102a/

as a rule if diode test can light an led then it's atleast 2v on the probes.

[redwire]

It's not your multimeter. Diode Test/Continuity is not even 1mA at less than 3V (for the Zotek)- that will not damage anything.
It's your cheap shit charger that you won't tell us about.

Measure ACV between PE ground and the laptop you are fixing.

[CapLeaker]

I have not destroyed anything yet using the diode mode on my DMM's. Unless I slipped with the probe and shorted something out.

[petehall347]

dont go anywhere near very high voltages especially if you forgot to swap your leads back from doing current measurement and have bypassed the fast acting fuse . wont matter anyway as it will toast your meter in an instant . i still have 3 expensive meters to fix after doing such things . they dont like thousands of volts .

[Sofian75]

It's not your multimeter. Diode Test/Continuity is not even 1mA at less than 3V (for the Zotek)- that will not damage anything.
It's your cheap shit charger that you won't tell us about.

Measure ACV between PE ground and the laptop you are fixing.

Sorry bench supply is this one.

Measure ACV between PE ground and the laptop you are fixing

How do I do that?

[redwire]

That bench power supply is pretty strong, you set it to 19VDC? What current limit?
How do you turn this on and off? Disconnect wire from laptop or use mains on/off switch?
If the power supply is low quality it can overshoot past 19V on power-up or power-down. Or if the cable/wiring is long it can damage the laptop input due to voltage spike.
Either that or you are clumsy and shorting out IC's with the multimeter probes when making measurements.

The power supply - did you ground it or not? What about your workbench.
The green and black jacks, what is the voltage between them, or is there a jumper?
If you can't measure voltage like ACV between ground to DC output then I think maybe work on your skills.

[harp]

In diode mode measurement, power must be disconnected, to get proper reading. I not sure even if on that setup you can cause any damage to dmm or device if device is powered.

But, I think and feel that root of your problem is cause by poking arround with probe tip while the power is connected. You must be extremly careful if your measurements is took from eg. qfn leg dirrectly, to not move (roll) tip between measurement leg and one by side. To damage chip while it is in power up state, there be suficient only one probe tip on wrong place - about 0.2mm distance from right measurement point location.
To avoid damage always when you can do, took measurement on exposed legs of some components, like resistor, capacitor or testpoint, who is directly connect to desired ic leg. There is much more room...
Is this match to your behaveour, can you recognise yorself in it?