RE: [CAD_CAM_EDM_DRO] Re: How do I test IC SN74LS541N on PCB?

If you are at all competent soldering then just replace all 20(?) chips.
You can check for solder bridges with an ohm/diode check on a meter much
faster than checking function of each chip individually.


I think you'd find a heat gun useful for unsoldering in this case.

if you use a simple heat gun with just hot/cold switch, you will want to
start with the gun far away and slowly bring it closer to the device to
be removed ON THE BOTTOM OF THE BOARD WHERE JUST THE PINS PROTRUDE
ASSUMING TEHSE ARE THRU_HOLE DIP PACKAGES. (you may want to craft a
funnel to focus the air to a ~1/4" spot)

you'll see the solder melt along all the pins. If you apply light
tension to the device it will just pop out when all the solder goes
liquid.

You can go back with a solder pencil and desolder wick/braid to clean up
excess solder.

The first device might take a minute or two of trial and error. The rest
will go really fast.

When installing new parts be liberal with flux and slightly stingy on
solder. Don't keep feeding solder once there is a good fillet around the
pin, else it will accumulate on the other side of the board and possibly
cause shorts on the top (assumes DIP packages). Solder wick can correct
this if it happens.

Fixing solder shorts is probably safer than excess testing/handling.
If you know there is a problematic design issue you may want to solder
sockets (generally I wouldn't do this, over time DIP sockets are less
reliable).

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Bruce
Sent: Monday, February 13, 2006 12:56 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: How do I test IC SN74LS541N on PCB?

The IC's are soldered in and I could plug the card in for testing but
it would be very time consuming to get at all the chips.
I am confident I can unsolder and solder in new chips, I have done
this before but I figured the less I solder the less chance of
damaging someting
I have a very basic knowledge of electronic and when I looked at the
datasheet on this chip I was lost.
I thought one could bench test each chip one at a time by supplying
the proper voltage 5 vdc and ground to the chip, supply the gate with
high or low current then input 5 vdc to each input and checking the
output to see if it is high or low depending one how the gate is set.
Sounds like I was wrong on this part, but if it could be done, would
supplying 5 vdc to the gate make it high and supplying nothing make it
low? Would I supply the input with 5 vdc or nothing and check the
output for high or low compared to what the gate is set for.
Would I fry the chip if I put 5 vdc to the input, maybe I need to use
a pulser, I have one although I am not positive how it works.
The machine the board it out of is for hobby use so I have nothing to
lose by trying to fix it myself.
Clear as mud?









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