robb wrote:

"Eeyore" wrote in
message ...

robb wrote:


i have a micro-controller board ....
i believe the 32v shorted with 5V
blew one fuse link. the fuse link was replaced with same
and when powered all three fuses blown.

So....where does one start to diagnose such a *big* problem ?


Well .... if the 5V supply went seriously high, the chances are

it's all fried.

:-(


there is a 630 mA Busman type fuses on all the lines i hope that
saved things ? but the fact that i am getting a short detected
between 0V and 5V line has me worried maybe thats good i do not
know hopeful someone can give me an method for finding problems ?


Have you tried powering the pcb from an external stabilised 5V

power supply ?

The very first thing to look for is a clock oscillator (and

valid reset signal).

Get the data sheets for those 40 pin chips, identify which one

is the micro and

scope the relevant pin(s).

What are the 40 pin chip numbers btw ?



one is the Phillips MAB 8051 micro,
then SRM 2017 Static RAM,
and NEC 8547E7 (D23256) ?? - can't find data sheet

then dual full bridge driver - L298
comparator - LM393 LM339 etc
some nor buffers and and and invertor pkgs

thanks again graham i really appreciate some help,
i can handle small problems but potential catastrophics like this
is a bit over

thanks
robb


Graham


I use a low ohm meter (Kelvin), it's very good at
tracking down the nearest point of the short on the
board.
You may want to look at capacitors. Especially
tantalums, they short very nicely many times leaving
nothing but ash.





--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5