what are these 8pin smd parts - serial interface

They look rather thick, so may be optoisolators.

I'd guess an HCPL-0452 optocoupler for one. The connections seem to match with the inputs and NC pins, and the Vcc/Gnd seem to make sense with the 200/330 ohm voltage divider if there's a 5 V supply. Serial input isolator and level translator?

The "300" is most likely from the same manufacturer, what with the similar marking placement and style, but given the ubiquitous 300 thou pitch form factor, there are a cubic butt-ton of parts ending in 300.

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Rich Webb     Norfolk, VA

Yes, my first thought, but the traces don't follow pattern for the

8pin optos I checked. Tried dual transistor out, and dual hi-speed with Vcc and Gnd on output (pins 5 - 8) side.

Grant.

Thanks! Yep, just checked the datasheet, looks very likely :)

Yes, it's a 5V supply, a blown 78L05 is on other side of PCB.

That's the problem I had, sites I searched refused to do a proper *300 search and returned all sorts of unrelated stuff. Maybe now I can narrow down to the two manufacturers I found with a datasheet, Fairchild and Agilent.

Thanks, Grant.

HCPL-0300 or HCPL-2300 seems likely? Low input current opto-coupler.

Another couple views:

Grant.

Perhaps an HCPL-3000, which is motor controller interface/driver and so it matches with the application. Hard to tell from the picture, though. In that shot, it looks like pin 7 (which would be Gnd) is floating, so maybe not.

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Rich Webb     Norfolk, VA

Yep, that seems to match the footprint. Pin 7 on the HCPL-x300 has an internal pull-up so leaving it NC on the board would fit.

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Rich Webb     Norfolk, VA

Thanks for checking the footprints. Really appreciate it :)

When I repair the thing I'll add some protective components so withstands the abuse that busted it this time.

Grant.