19 Jan
2002
19 Jan
'02
3:28 p.m.
It turns out htat SCSISTUFF.COM was not where I ordered those things for $6,
folks, it was http://www.CableClub.com, in case anybody was wondering whether
I'd hit my head or something.
That's about $10 less than the comparable item from SCSISTUFF.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, January 19, 2002 7:01 PM
Subject: Re: Kinda OT but that what's true HW hacker do in a pinch.
circuit
That depends on the transformer. Sometimes it's an external thermal fuse
on top of the tape over the windings (looks like a small metal cylinder,
or sometimes a ceramic block). Sometimes it's under the very top layer of
tape. Sometimes it's under the windings, but can be pulled out from one
end. Sometimes you'd have to unwind the transformer to get to it :-(
And sometimes the primary is designed to be the thermal fuse. If it
overheats, the insulation melts, you get shorted turns, and it either
melts the wire or blows the current-operated fuse. Apparently the former
(wire that's designed to melt after the insulation has melted) actually
meets most safety approvals, and it's the intended failure mode of most
cheap wall-warts over here. Is it any wonder I can't stand the darn things?
>
>
> > Ouch! What ever happened to user-replacable fuses to handle such
problems?
Yes *there is* SMD 500mA fuse and zener diode but that is AFTER that
darned ceramic capacitor. That why wall wart died and capacitor
Brilliant!. This reminds me of a number of other safety features (and
also self-diagnostic features) that fail to work when a fairly common
problem occurs....
> > Many transformers have thermal fuses designed to open the primary
under such conditions. If you can open up the PSU box,
you may find a
replacable (with soldering iron and pliers) thermal fuse on top of the
transformer, or stuck under the tape covering the windings.
How diffcult to find this thermal fuse? This wart is hard to get voltages w/ 16VAC. Most I see are 9, 12 and
nothing of to find. I
had to make do w/ 12VAC for short term.
I'd probably buy a transformer (15V is common over here, and would be
near enough, I think). Mount it in an earthed metal box with primary and
secondary fuses, and a thermal fuse in series with the primary. Oh, and
add decent mains connectors. It may not be as neat as the original, but
IMHO it's safer and easier to repair. That's what I normally do for
missing/defective wall warts. Or sometimes I do it even if I have the
right wall-wart, if I don't think the latter meets _my_ safety standards.
-tony