I searched every possible combination of (mosfet transistor 630 121) with little success, including the datasheetcatalogue. Can anybody point me to the right direction? I think it is used in open collector type of output and is supposed to be a transistor but may be wrong. It has four pins and only says 630 and 121 in two lines. Here is the picture
opto couplers on the inputs, standard for motor controller? - series resistors also visible, tends to confirm.
Hi Mark,
thank you! will try to figure out how it works.
mvoltin:
It has four pins and only says 630 and 121 in two lines.
I see eight pins.
It is symmetrical. Sort of. Clearly a dual optocoupler.
That wodul probably make it a HCPL-0630.
Hi, yup, they are like HCPL-0630.
I have seen them before and replaced them with the HCPL.
I took a good one out of circuit on a bit of gear I was repairing and measured out as a basic HCPL-0630.
High Speed, TTL compatible.
Tom...... 
(yay my AFL football team won tonight, go CATS)