SGI Indy power supply: identify this diode?

After a recent power cut and a series of glitches as the power was restored, one of my Indys suffered a PSU failure. It's a Sony APS-81 171W unit, SGI P/N 060-0008-001. I've found half a dozen damaged parts, and I've identified a 150R 1W metal film resistor (R135), two trannies (Q105, a 2SC4304 and Q106, a 2SC2785) and a couple of small diodes. One of them (D116) appears to be a 6.2b2 (6.2V 1/2W) zener. The other one I'm not sure about. On the PCB it's labelled D113, and it's adjacent to the 2SC2785. It's very small, with a green band at the cathode end, and the legend "4B" in green - photos at https://www.flickr.com/photos/pnt103/albums/72157667056183978 Oddly, another Sony PSU I looked at had a diode there that looked identical except it's marked "4A". I have an idea what it might be but if anyone actually knows what family or type/value this is, I'd be grateful for any insight. -- Pete Pete Turnbull