VT100 PSU smelling.
tothwolf at concentric.net
Fri Jan 22 18:26:54 CST 2016
On Sat, 23 Jan 2016, Mattis Lind wrote:
> 2016-01-23 0:32 GMT+01:00 Peter Coghlan <cctalk at beyondthepale.ie>:
>>> R27 is part of the snubber network on the primary side of this
>>> forward-type SMPS PSU. But why it it getting so hot. Is it normal? I
>>> have completely forgotten how a VT100 smell when running...
>> Snubber as in a resistor in series with a capacitor across the primary?
> Yes. It is a R, C, D network.
>> If so check the capacitor for leakage (electrical, not liquid) or being
> I don't have a ESR meter or similar. It is not shorted at least and the
> resistance is in the several mega ohm range when measuring in circuit.
> Are they likely to go bad in a non catastrophic way?
They can. The translucent yellow Rifa (now owned by Kemet) class X/Y
safety capacitors in particular have a 100% failure rate and are on my
replace-on-sight list. They usually begin to show visible signs of
cracking in their outer casing before they finally go out with a bang. It
seems to be due to chemical decomposition of the paper insulator which
swells over time and causes the case to crack. I usually replace them with
a film capacitor from Epcos of the same value and safety class.
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