VT100 PSU smelling.

[Tothwolf]

On Sat, 23 Jan 2016, Jules Richardson wrote:
> On 01/22/2016 06:26 PM, Tothwolf wrote:
>
>> 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's a well-known fault, but has anyone ever known one fail and actually 
> cause any damage (other than to itself)? AIUI, they're there to reduce 
> noise from the device leaking back out onto the AC supply - a system 
> should run quite happily without them.
>
> I've had maybe four or five fail on me over the years, out of several 
> hundred systems. They're a definite weak spot, but given that I've never 
> heard of one damaging anything it's the sort of thing I'd consider doing 
> only if I was carrying out some other repair work on the PSU.

I've seen blown/cooked series resistors (which I replace with metal oxide 
resistors) and sometimes a blown fuse.

I always replace them whey I'm doing other work on a psu, however I'm not 
sure I'd knowingly leave one in place since they let out a lot of smoke 
when they go.

>> I usually replace them with a film capacitor from Epcos of the same 
>> value and safety class.
>
> Is the voltage rating on the US ones different (new vs. old)? I can't 
> remember now. I know all the old UK ones seemed to be 250V, while modern 
> parts were rated at 275V.

Higher voltage parts are available but they are more expensive. I've seen 
300V, 350V, 375V and even 400V safety rated parts.