"Arfa Daily" wrote in message
news

"robb" wrote in message
...

"Tom2000" wrote in message
...
On Tue, 6 Nov 2007 07:34:53 -0500, "robb"

wrote:



there was no obvious visual evidence of any smoked parts
that
i
could see , only the middle busman fuse was blown after the
short

and that seemed to be related to power going to the L298

thanks for all the help,
robb


Tough problem with all the ICs soldered in.

Chances are that the 32 volt supply is only used for the
L298s,
as you
suggest. It also appears that you can unsolder these
without
damaging
any other parts on the board. (Even if you have to cut them
out,
they're still available and easy to replace.)

If your short doesn't disappear after pulling the 298s, try
unsoldering any of the caps near those chips.

Leave unsoldering any ICs as your very last resort.

I'm now bowing out of this discussion and leaving it to the
experts.


Thanks Tom,
i really appreciate any comments and help

i unsoldered one of the L298 and it has no shorts so now the
next
then i will do a trace of the 5V lines until i can learn
something usefull about the interconnections.

i hate working blind and re-tracing things when i could just
look
on a schemat.

so thank you ,
robb


If you have a photocopier or flatbed scanner available to you,
and the board
is not too big, I sometimes find it helpful, where no
schematics are
available, to scan and print out the underside of the board,
then take a few
minutes to draw on an overlay of the major components. Coloured
felt tip
pens or highlighters can then be used to trace round critical
signal and
power tracks. Makes it a lot easier then when metering for the
problem. I
have found a digital ESR meter - such as the Dick Smith - which
is capable
of accurately measuring and displaying very low ohms, can be
useful for
tracking down dead shorts on rails that go all over a board.

Arfa


thanks Arfa,
for helpful ideas.
i used a slightly cruder method last night.
i used a green fine tip sharpie to draw directly on top of the
PCB resist 5V tracks because they zig-zag back and forth accross
the board front to back and i kept loosing track (pun intended)
of where i was testing

the green sharpie about same color as resist shows up as shiny
line an dnot to unsightly

i like your idea as it will help keep track of test points tried
as i can record the test values next to points

thanks again for the ideas/help
robb