is that the current device or the one that got zapped ?
I found a 8574a in my junk box and fed your code into it (no lcd) and it seems ok (address is $78 for a version)
the attached pcf8574a.txt file is really a salea logic data/setting file and should be renamed to pcf8574a.logicdata , if you don't have a salea logic analyser you can download the software from salea logic and view the complete data
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