Identifying Some SOT-23 Components

Rob Jarratt robert.jarratt at ntlworld.com
Thu Jul 13 17:24:50 CDT 2017


I am still trying to fix my DECstation 220 motherboard. It suffered damage
from battery leakage and I have found that replacing a couple of components
has improved matters in that the BIOS now seems to execute consistently and
the processor does not keep resetting. However the BIOS seems to be in a
loop very early in its processing, I get no beeps and no video output. I
actually have a spare motherboard, but that had battery leakage too and has
very similar symptoms.

 

The problems I have had to fix have been mainly in the area where the
battery leaked (but not entirely), and I would like to pre-emptively order
spares for all the parts in the leakage area. The trouble is there are a
couple of components I am having trouble identifying and I was hoping
someone may be able to help. They are all in what I believe to be an SOT-23
package.

 

The first appears to be a surface mount transistor (it is labelled "TR2"),
the markings are not very clear. On one board it seems to be marked "1N",
and on the spare it is marked "S1A". Neither of these seem to turn up on the
reputable sites, so I wonder if anyone knows of a good equivalent?

 

The second one is marked "A6" followed by an indistinguishable mark,
followed by what looks like an "E" or a "5", one of them looks like it could
possibly be "A6S". I have found some A6V2 Zener diodes, but I have no idea
if these components are diodes, although it does look like one of the pins
is not connected, and they are labelled "DS1" and "DS2", which makes me
think they really are diodes.

 

On the basis of the information above, can anyone offer suggestions for
possible replacements?

 

Thanks

 

Rob



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