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"NOP" Fault Finding Technique in 2018

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I have a question about a fault finding technique I learned sometime last century … about making a micro run continuous “nop” instructions (using 8085 and Z80 etc).

I have a board that uses a separate micro, SRAM and a flash memory chip - that I’m trying to fault find.

Have replaced the flash chip and SRAM to no avail … yet that chip works fine on another board.

(The board displays the same symptons I see when it has a crook flash ... but in this case, a new flash didn't solve it)

At the moment, all I can recall to do is to check DC levels, clock signals … then what?

I’d often thought about using the nop technique but never did because of the effort needed to remove and swap around large smd chips. Now that I have a decent hot air desoldering tool … it feels more doable.

The micro is a H8S/2350. How hard (or worthwhile) would it be to write a routine to load on flash and check the result?

... and if worthwhile ... how does one go about doing that.

Thanks for any help.
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