PSU Charge Dissipation

The PSes I've seen have a bleeder resistor, usually about 330k, across the HV capacitors to remove any charge when the power is removed. This takes only a few tens of seconds. The PS can work with an open bleeder resistor, so as a precaution you can measure across the caps with a DMM, and you should get zero volts. Of course take all the necessary precautions such as make sure the PS is unplugged, etc.

I've done this to several PSUs. The easy way is a strong pair of side cutters and snip trough the last set of legs which support the grill. No need to get inside the PSU nor remove the PSU from the chassis. Now since this will leave a big hole with fan blades close by, you ought to get a wire fan guard to cover the hole. Crank the guard's legs to provide a 1/4" stand-off to reduce noise susceptibility and fit them to the fan's mounting screws.

A picture is worth a thousand words - have a look at the 'Recent Build' article on my website below. Also a bit in there about flatting heatsinks, too.

To answer the original Q leave it overnight with the mains supply removed, NOT simply shutdown.

-- Graham W

PGM-FI page updated, Graphics Tutorial WIMBORNE Wessex Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

I should have mentioned that I have already done just that.

What I want to do now (which will definitely be awkward/risky with the contents still in place) is to increase the diameter of the exhaust aperture because it isn't quite wide enough. Consequently, airflow hits the aperature edges causing turbulence and hence increased noise. You'd think that nowadays manufacturers would check something so obvious, but then it is 6 years old!

As you can see, to achieve the above I really need to empty the box of the circuit board and components.

It's wise to remove the electronics from anything before you do any work that might make metal shavings. They tend to short out thing when they fall onto the PC board.

Agreed!. If you need to file edges then it is advisable to remove ALL components from the metalwork to avoid tiny shards getting into things like fuse holders, switches etc.. It is possible to shroud the other electronics stuff if you can attach, temporarily, a fine woven cloth to prevent the filings migrating to places which could cause trouble but it would restrict your ability to get enough stroke on a hand file. Nonetheless, that technique has worked for me.

If you leave the PSU unplugged overnight there won't be any serious charge in the capacitors and as a safety measure/confidence booster, you could dicharge any remanent charge with a jump-lead and a 100kohm resistor connected across the HV caps for a minute or two after an overnight resting period unpowered.

As an incidental comment, I reduced the fan turbulance on my GF4-Ti4200 by simply removing the fancy anodised plate which covered the fin set. The hole in the middle was the offender here and further checks on temperature rise showed that it was really only there for decoration and branding!

HTH

--
Graham W   http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE   http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK  Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.