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diagnosing circuit boards

K

kb

Jan 1, 1970
0
Can someone offer me some basic guidlines on diagnosing circuit
boards? I am in the process of working on a signal conditioning board
with approximately 10 surface mount IC's (op amps, isolating amps,
instrumentation amps etc). Some of these IC's are blown. I have no
circuit diagram.

My question is with the individual IC's. How feasible is it to test
each IC individually (in circuit) to see if it is functioning
properly? It would seem to me that just touching a multimeter to such
sensitive circuits change the behavior and possibility not give a
correct view of what is really happening (like open loop op amps and
comparators).

Anyway, any guidlines for diagnosing in-circuit IC's??

thanks much - a confused beginner
 
Q

Quark Ng

Jan 1, 1970
0
kb said:
Can someone offer me some basic guidlines on diagnosing circuit
boards? I am in the process of working on a signal conditioning board
with approximately 10 surface mount IC's (op amps, isolating amps,
instrumentation amps etc). Some of these IC's are blown. I have no
circuit diagram.

My question is with the individual IC's. How feasible is it to test
each IC individually (in circuit) to see if it is functioning
properly? It would seem to me that just touching a multimeter to such
sensitive circuits change the behavior and possibility not give a
correct view of what is really happening (like open loop op amps and
comparators).

Anyway, any guidlines for diagnosing in-circuit IC's??

thanks much - a confused beginner


Do you know what it was suppose to do if it was working? This info
would really help.

-Quark
 
K

Ken Taylor

Jan 1, 1970
0
Can someone offer me some basic guidlines on diagnosing circuit
boards? I am in the process of working on a signal conditioning board
with approximately 10 surface mount IC's (op amps, isolating amps,
instrumentation amps etc). Some of these IC's are blown. I have no
circuit diagram.

My question is with the individual IC's. How feasible is it to test
each IC individually (in circuit) to see if it is functioning
properly? It would seem to me that just touching a multimeter to such
sensitive circuits change the behavior and possibility not give a
correct view of what is really happening (like open loop op amps and
comparators).

Anyway, any guidlines for diagnosing in-circuit IC's??

thanks much - a confused beginner
You can generally test IC's in circuit, but without a schematic you'll be
pushing the proverbial up-hill. I suggest tracing out the circuit, which
will also give you an insight into how the circuit works.

Ken
 
K

kb

Jan 1, 1970
0
Can someone offer me some basic guidlines on diagnosing circuit
boards? I am in the process of working on a signal conditioning board
with approximately 10 surface mount IC's (op amps, isolating amps,
instrumentation amps etc). Some of these IC's are blown. I have no
circuit diagram.

My question is with the individual IC's. How feasible is it to test
each IC individually (in circuit) to see if it is functioning
properly? It would seem to me that just touching a multimeter to such
sensitive circuits change the behavior and possibility not give a
correct view of what is really happening (like open loop op amps and
comparators).

Anyway, any guidlines for diagnosing in-circuit IC's??

thanks much - a confused beginner

I do know what the output should be for a given set of test inputs for
the overall board

I'm not sure I could trace the board - it is multilayer (at least 3) -
I guess its possible but seems very hard
 
B

Bill Vajk

Jan 1, 1970
0
I do know what the output should be for a given set of test inputs for
the overall board
I'm not sure I could trace the board - it is multilayer (at least 3) -
I guess its possible but seems very hard

In my personal experience a blown IC *usually* shows either an
open or a short when an ohm meter is applied across the power
terminals. I always use an analog meter and test both directions
(polarities.)

Before anyone jumps me on this, yes, there are other failure modes,
but I wouldn't skip this simple test as it is pretty dispositive
about strong failures and you might be able to find the fault
that way.

The next stage is to use a logic probe. Things start getting fun
when you do that.
 
J

JeffM

Jan 1, 1970
0
a blown IC *usually* shows either an open or a short
when an ohm meter is applied across the power terminals.
I always use an analog meter and test both...polarities.
I wouldn't skip this simple test
Bill Vajk

and once you have determined it's a rail-to-gnd short at the board level,
connecting a current-limited power supply to the rail
to let the bad part get warm can sometimes help isolate it easily
--the old wet finger test.
 
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