[time-nuts] Thunderbolt PSU

[Mike S]

At 05:49 AM 7/22/2008, David Ackrill wrote...
>On plugging in a lead there was a slight 'buzz' and, on checking the
>outputs, no DC volts.  Checking the lead showed no AC volts.  So, I
>opened the plug and checked the fuse, a 3 Amp type - too big for the
>unit output really, but shouldn't have blown...
>
>Changing the fuse for a 1 amp type, and plugging back in showed no
>output voltage again.  Checked the business end of the lead and 
>there's
>AC volts still there.  I'm guessing, from experience of these PSUs in
>the past, that there's a fuse inside the unit which has also 
>blown.  If
>so, I guess I have a faulty PSU?

Most switching supplies require a minimum load to operate correctly. If 
the output is just open, and you don't see any voltage, it doesn't 
necessarily indicate a problem.

I wouldn't use it with the Thunderbolt until you get the issue worked 
out, though - you don't want to blow it up if there's been a failure in 
the power supply's protective circuits.

According to a previous list message, a running Tbolt takes about
160mA at +12V, 250mA at +5V, and 3mA at -12V. So maybe a 75 Ohm, 2 W resistor 
across the +12V and a 20 Ohm, 2W resistor across the +5. If those are 
covered, the -12 can probably be left open without issue.