VT100 PSU smelling.

js at cimmeri.com js at cimmeri.com
Fri Jan 22 14:48:22 CST 2016

On 1/22/2016 2:54 PM, Mattis Lind wrote:
> Short: R27 in my VT100 PSU is hot and smelling. Why?
> Long: I think it has been 20 years since I powered up this VT100 so I did
> it carefully. Used a Variac and a bench supply. It switched just fine and
> delivered the steady 5V out when the input was at approx 50V (115V input).
> All the other voltages looked fine at full AC input. But there was this
> little smell from R27.

You don't use Variacs with switch mode power supplies... not unless you 
want to burn them up.   I'll sometimes use one, but only to provide a 
very fast soft start.  Even that's risky.

- J.

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