Help with ICL power supply fault (Farnell SMPS)

[Randy Dawson]

remember in a pinch you can wire two step down transformers back to back...

> From: cclist at sydex.com
> To: cctalk at classiccmp.org
> Date: Fri, 11 Apr 2008 09:31:49 -0700
> Subject: Re: Help with ICL power supply fault (Farnell SMPS)
> 
> On 11 Apr 2008 at 2:53, Tony wrote
> 
> > The right way to do it, of course, is to use an isolating transformer, but
> > not everybody has one of those in the workshop. 
> 
> This is something that anyone who owns a screwdriver and a soldering 
> iron should have if one intends to go poking around in the "guts" of 
> powered equipment.
> 
> Fortunately, it's easy for us in the US and Canada (and Japan) where 
> mains power is 120v.  Just about anything with a transformer in the 
> PSU (still pretty common in audiophile gear, as are large 
> electrolytics) has been constructed with a "universal" 
> 100/120/220/240 transformer, meaning that there's usually a split 
> primary, so one primary winding can be used as input and other, as 
> output.  (the other windings can be left NC).
> 
> Those in 220/240 volt-land can use two transformers of the same 
> secondary voltage connected back-to-back as an isolation method.  
> Another option is to scavenge a transformer from a UPS--it's very 
> common that the same transformer is used to charge the batteries and 
> as an inverter output, meaning that there are often two sets of line-
> voltage windings present.
> 
> I have a box with a large scavenged UPS transformer and a Variac for 
> my workbench--and its own 5 amp fuse.  Not only do I get isolation, 
> but I can adjust the output voltage--and I don't have to rely on 
> tripping the 20A distribution panel breaker when something goes 
> wrong. 
> 
> This is particularly important with some of the old hobbyist gear--
> IIRC, the MITS Altair ran a couple of bare PCB traces at line voltage 
> to the front-panel power switch. 
> 
> Those with big iron with high-current line-side requirements are 
> advised to use the "one hand in a rear pocket" technique when poking 
> around in a PSU.
> 
> Cheers,
> Chuck
> 

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