On Wed, 4 Mar 2020 17:31:34 -0800, Robbie Hatley
wrote:

At my workplace, I'm often faced with circuit boards which WOULD be
repairable, if not for the fact that the CPU on the board is fried.
(These CPUs are not like the CPUs in PCs; they're 15mm-square
$5 8-bit 8MHz 100-pin CPUs with 25 pins on each side, surface-mount
soldered directly to circuit boards.)

Repairing these boards is maybe impossible, but I'm investigating
options. The 2 main problems that would have to be solved a

1. Remove CPU from board. (CPU doesn't need to survive, but board does.)
Heat gun? (Might damage surrounding components.)
Solder bath? (Might unsolder surrounding components.)
Cut pins? (Might damage traces.)
OTHER???

2. Extract software from good CPU???
(The board maker won't supply the software due to copyright issues.
The boards DO have programming headers, presumably for use with an
external programming module which connects to a PC via USB; but I
don't know if such programmers can work in reverse, READING software
from a CPU instead of WRITING to it.)


Anyone here have some ideas regarding these two issues?

You can desolder gull-wing leads, pin by pin, by slipping a
1-2mil nickel-iron strip between pin and pad, while heated.

The strip can be progressively advanced along the pins, as
each is freed. The nickel content prevents solder adhering
to the strip.

These strips are salvageable from old stick-on anti-theft
devices, often found on CD cases or small electronic device
packaging. You'll find 2x1mil and 1x2mil strips in each one.

These strips will fasten into a standard exacto knife handle,
and can be angle-cut with scissors, bent or restraightened
to your prefered shape. 2mill probably is easiest to start
with.

An angle cut works best to start from a package corner.

No point in removing a part that can't be sourced for
a replacement, including code.

RL