Bob,
Other than cutting traces or removing chips, there is no easy way to
check for such a shorted condition.
I do suspect that the MAX1406 chip (U4) is the one to remove first
because it is the most likely culprit. The EL5146 chip (U6) is also on
the suspect list.
Before desoldering, remove U1 from its socket and see if the 5 volt
output is restored to normal.
If you do not have adequate desoldering tools, I suggest that you order
both ICs and a regulator, clip the leads on both ICs and remove the
leads one at a time - remove the excess solder with solder wick and
clear the hole with a round toothpick or a stainless steel needle. The
replacement ICs are much more inexpensive than the entire board, so it
is prudent to just replace the ICs wholesale rather than tearing up the
board in an attempt to preserve the suspect components.
73,
Don W3FPR
Bob G3PJT wrote:
Hi
My CAT just stopped working and I have found that there appears to be
a low resistance on the 5v rail which supplies the PIC / 232 interface
chips. This pulls the 5V rail down to 1 v with the result that the PIC
and 232 interface chips are not operating and the 78L05 at U3 is
rather hot and bothered.
Before I get the PA board off the heatsink and start desoldering chips
has anyone any idea of checks I could do to localise the problem
73 and thanks for any info
Bob G3PJT
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