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.)
I can't tell what type of package that might be. My best guess(tm) is
one of these:
https://en.wikipedia.org/wiki/Quad_Flat_Package#TQFP
A maker and part number for the CPU would be helpful.
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???
Hot air SMD desoldering station. Something like this:
https://www.google.com/search?tbm=isch&q=hot+air+smd+desoldering+station
You'll need a nozzle to match your chip:
http://new.ldbenterprises.com/smd-rework-station-nozzles/
You'll need to know the IC package type to order the proper nozzle.
There are videos on YouTube on how to use these:
https://www.youtube.com/results?search_query=smd+qfp+desoldering
You'll also need flux and flux remover. A good binocular microscope,
fan to blow away the smog, and an aluminum foil heat shield, are quite
helpful.
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.)
Most uP firmware is copy protected. That may not be possible. You'll
need to get the instructions from the manufacturer of the product. If
the device has a JTAG port, you might be able to do something with
that.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558