Just a word of warning re: optocouplers as per the O/P, they can be damaged by either excess and/or prolonged heat, the following extract was taken from a technical bulletin issued by Sharp wrt the PSU repair on a few of their CTV chassis.
Quote:
The opto coupler is easily damaged by excessive heat while soldering, so remember to keep your
soldering iron temperature turned down to 250oC or below, and not to solder for more than 10 seconds
on each leg. If these conditions are not met the transparent barrier between the LED and opto
transistor will be damaged. Note that sometimes the set will work for several weeks or months before
failing if the opto has been damaged during fitting
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Shades of old Germanium devices
