ant, wilson is right 40106, ne5534 and lf412 need need to be tested/replaced, the best advice is to do them one at a time rather than all at once, so you can trace the problem.
the chip sockets idea is also very good advice, you can always remove them as final task when you finish(if you like your chips hard soldered),
i have never been convinced it matters, what matters more is the quality of the sockets.
even the cheapest sockets will work for your task,when you have 4 chips that work and you have basic function you can remove them and install the working chips permanently.
the chip sockets idea is also very good advice, you can always remove them as final task when you finish(if you like your chips hard soldered),
i have never been convinced it matters, what matters more is the quality of the sockets.
even the cheapest sockets will work for your task,when you have 4 chips that work and you have basic function you can remove them and install the working chips permanently.
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