SGI Indy power supply: identify this diode?

[Pete Turnbull]

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