You can safely test silicon devices, if you use a multimeter with
"low power ohms" setting. It applies a voltage not intended to
cause forward conduction in the silicon chips.
If you lost the manual for your multimeter, you can verify this by using
two multimeters. One multimeter set to "ohms". The second multimeter
set to "volts". The "volts" multimeter will show you a rough idea
of the open circuit voltage that the "ohms" meter is putting out.
(Connect red to red, black to black.)
Test all the "ohms" ranges on the meter, to understand which
ranges are "high power" and "low power". If an ohms range doesn't
put out more than 1 volt open circuit, then it should be relatively
safe to use on just about anything. For the highest resistance
ranges, the results need some interpretation (since the voltmeter
has a finite input impedance of its own)
The $100 The $20
meter meter
Range Ohmmeter Voltmeter Assumed Confidence
Reads Reads Power type
Beep Infinity 2.66V High
Diode infinity 2.67V High High on purpose, for diode
test
200 Infinity 1.01V Low
2K infinity 1.01V Low
20K Infinity 0.48V Low
200K infinity 0.43V Low
2M "0.995" 0.23V Low OK, see interpretation
20M "0.99" 0.04V Low
2000M "001" 0.27V ??? suspicious
(Note - a separate set of tests were done, and the "ohms" multimeter
never applied more than 1 milliamp of current to the test leads. Typical
silicon clamp diodes are rated for about 10 milliamps. So there is
no danger from the level of current flow either.)
In the 2 megohm test case, the "volts" multimeter appears to
have only a 1 megohm input impedance. Half of the open circuit
voltage is across the "volts" multimeter, and half is across
the constant current source inside the meter. We could conclude
from that, that the actual open circuit voltage applied
by the multimeter, is 2 * 0.23 volts or 0.46V. And that is suitable
for low power ohms. So you actually have to stare at the display
on both devices to understand what is going on.
My suspicion is, the "insulation test" range on my multimeter, is
actually high power ohms. It is pretty hard to test insulation,
with a low voltage. Insulation testing would normally be done
with a "megger". Since I am suspicious of what I see for the
2000M range, I likely would not switch to it while working on
the average PCB.
There are quality voltmeters, with much higher input impedance
than my $20 "volts" multimeter used in this test. For such a
device (perhaps a $1000 unit), I likely would not need interpretation
except for the last test case. And the voltmeter in that case, could
tell me what the open circuit voltage is, correctly, for the
rest of the ranges.
The $20 meter is the one I lend to friends
So there are six ranges on my $100 multimeter, that I'd use on a DIMM.
Without being concerned about any side effects to the silicon.
Some older meters, like my analog Simpson, are a bit meaner.
They apply nine volts open circuit, and would be unsuited
for this purpose. I could have run the same set of tests for
my Simpson, but there is no point, because I simply wouldn't
use it. My Simpson is good for volts "trend analysis", as digital
meters aren't perfect for all purposes. There are still
occasions for reaching for my oldest multimeter. "Ohms" would
not be one of those reasons.
If a person had concerns about any silicon device they were
working on, they could look in the datasheet for inspiration.
I haven't done that in this case for the memory chip. I'm reasonably
confident, that the six tested ranges on my multimeter, would
be safe enough.
HTH,
Paul
