I got some VOM1271 photocouplers from aliexpress. Yes, I know, buyer beware when it comes to aliexpress, but this was from a seller I considered trustworthy. I've bought from them before, they've got 99+ rating. The price wasn't suspicious either, about €10 for 5pcs.
As it turns out they were duds. First clue was that the physical dimensions don't match. The package was white, which isn't mentioned in the datasheet but all the photos I've seen have been black. And the package should be square, not rectangular like these traditionally are.
Electrically they perform pretty oddly. The positive going waveform looks fine. But at turn off.. I have no idea what's going on there. I tested 3 separate chips, all look the same. I've attached a scope picture of the output, the light blue waveform is a TLP3906 from a reputable seller as a reference.
Naturally I opened a dispute but aliexpress decided to give only partial refund. I've had some funny decisions from them lately. Like ordering a double sided A4 copper clad, receiving a single sided A6. Partial refund. Another incident was that a seller demanded I pay them extra after I placed an order and refusing to cancel it. I sent aliexpress three messages and their reply was to ask them nicely. The seller eventually shipped the order, with a fake tracking number. At least that time I did get my money back eventually.
Just my small rant to start the day off nicely!