"clifto" wrote in message
...
robb wrote:
"clifto" wrote...
robb wrote:
I connected the 5v (through 450 Ohm) to the PCB 5v and 0v
lines.
i measured ~60 mA curent nothing warmed ...

That's pretty good. If you then shorted the PCB 5V and 0V
lines, you would
have 450 ohms across 5V and should read 11.1 ma.

i idecremented the
resistance by 100 for each iteration of testing the
measured
currernt increased slightly until i made it to (100 Ohms)
and
then the current spiked to ~+ 1.5A and the 7805 fried ?

To get 1.5A through 100 ohms you need to apply at least 150V
to it.

thanks for reply clifto,

i will have to believe you on the numbers

and although the numbers may seem incorrect from a
electronic
formulaic analysis i can only report what i see on the
equipment
i use and with the setup i use.

What I was trying to get you to realize is that there is
probably a
problem with your equipment, or with your understanding of its
use.
When the PCB supposedly draws over five times as much current
as a
dead short, it should tell you that what you think you're
seeing isn't
what is actually happening.

[trim]

If you used a 1/10 watt 100 ohm resistor, putting 5 volts
across it
should dissipate 2-1/2 times its capability, or 0.25 W. That
might
make it release smoke.


Thanks for help clifto,

i do realize what you are saying which is why i said, "i
consider operator error to be a possible problem".
this amateur horse brain needs some help getting itself in front
of the cart.

i've been told that the 73 Ohm resistance between the 5V and 0v
is not so bad and is somewhat hopeful that i did not incinerate
all the ICs.

if i can diagnose without removing the ICs then that would be
great, otherwise i may need to fall back to brute force
diagnostics and remove ICs one at atime and check things and
iterate .

i was hoping to learn something a little more sophisticated.

i was uing 1/4 watt resistors.

i plan to try the capacitors to prevent oscillation,

thanks for help and for any more ideas you may have,
robb