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Rob[_40_] Rob[_40_] is offline
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Default How to replace bad CPU on circuit board?

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?


That kind of chips is actually EASY to handle, compared to the newer
style BGA where you only see a square chip directly mounted on the board
and no pins whatsoever. See the other replies.

The problem will be the programming, you need to investigate that first.
Programmable CPUs usually come with a readback prevention and when that
is activated (it is an option during programming) it will be difficult
or impossible to get the software, and then the whole replacement thing
is not a topic anymore.

What is the part number of the CPUs?