Describe what
the plug looks like (number/configuration of
the pins), first of all.
Great minds think alike :-). That's my first question as well. 2 connections
implies an internal regulator, a lot of pins probably means it wants
'standard computer-like' voltages.
OK, Great Minds, there are two pins in the standard center/outer config
associated with most wall warts.
If there's
any way to open the box up, look for any obvious rectifiers and
Are the computers you can't open up?
There are few computers easier to open up than this one. Refer to figure
1:
http://www.yowza.com/classiccmp/oddball/ht35.jpg
tantalum/elecrolytic capacitors near where the power comes in. This'll give
a good indication of the polarity and a rough guess at the voltages.
Also, are there any transformers/large inductors in the PSU, implying a
switching-type regulator ? Any power devices or chips with sane numbers?
You might be able to deduce a lot from that.
There seems to be a transformer that helps out with the display voltage,
but it's the only thing in the box that's hard to get to. I can tell it's
on a PCB labeled P/N 665-0454 (just in case it matches one sitting by
you).
Here's where software-boy gets in trouble. There's a part near the DC-in
that looks like it by be a transistor. The board label is D3 and the part
is labeled 1R OE 30WQ0AF (maybe). The center conductor buzzes on the
outer two pins of this three-pin device. Also nearby is a 16V 470uF cap,
but it's not easy to trace the connections. The center conductor buzzes
with what I think is the negative terminal of a tantalum cap on the
trace-side of the board.
Are those clues enough to nail down the polarity?
-- Doug