SGI Indy power supply: identify this diode?

[Pete Turnbull]

On 26/03/2018 16:08, Camiel Vanderhoeven wrote:
> 4B would be a 2.2V zener; 4A would be a 2.0V zener, so that’s odd indeed...

That's the idea I had...

Except it's not a zener, or at least not anything like those.  I took 
one out of another (working) supply, and I can tell it has a forward 
voltage of 0.2V, so it's presumably a Schottky diode of some sort.  I 
can also tell it's not a low-voltage zener; the reverse breakdown 
voltage is more than 35V (the highest my bench supply goes up to).

I'm hoping I don't have to breadboard a 1kV supply and find a lot of 
multi-megohm resistors to try and estimate the breakdown voltage - and 
then guess at the forward current rating.

> On 3/24/18, 9:47 PM, "cctech on behalf of Pete Turnbull via cctech" <cctech-bounces at classiccmp.org on behalf of cctech at classiccmp.org> wrote:
> 
>      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