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PSU Modding - Three pieces from one

E

entitydev

n00b
Joined
Aug 27, 2005
Messages
7
I've had an ITX mobo sitting around for a while waiting to be built up for my daughter's computer. I bought a case off TradeMe (think eBay) but when it arrived found it was for a mini-ITX board. The mobo fits inside (with a couple of extra spacers for support) but the stock powersupply is about an inch & a half too wide to fit in the case at the same time. So, I tore it to pieces.

[ Please note, I could have just got a PicoPSU but why spend $$ when you can mod for free? ]

The PSU actually contained four separate PCBs, one main, one smaller that ran parallel to the main board, and two that attached at 90 degree angles. I've removed them all from each other, extended & loomed the wires so that each section fits in an empty space inside the case. Each PCB sits on spacers and is covered by a mesh cage I made from flyscreen mesh. I wanted to lose the stock 60mm fan that came with it so I've replaced all the heatsinks with larger versions.

It works fine, but there are two things that concern me:

1. I'm getting some nasty interference now that it doesn't have a solid metal case surrounding it. Is this the only reason or will the extra runs of wiring have an effect?

2. One of the PCBs was screwed onto a heatsink on the mainboard - there are no traces on the pcb where it attached, but a heatsink on the pcb was touching the heatsink on the mainboard when screwed in place. As long as both heatsinks are grunty enough, will this be a problem?

I'll see if I can find my camera to take some pics, might explain it better :)
 
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Are you experiencing the interference with the computer case open? If so, try closing the case, and see if the interference is still there. While you're at it, make sure your case is connected with a ground wire to the PSU. That's important. The long lines *might* be exacerbating the interference by acting as antennae, but without knowing exactly what kind of signal is going through them, I can't say for sure. If it's something related to the PWM voltage control, it's likely, as you're talking frequencies in the hundreds-of-kilohertz range.
 
The interference might be from the transformer in the PSU. I had a similar experience with an mITX system I built a while back, until I bought a suitably small PSU that fit with it's housing intact. The interference I had was a "hum" in the audio.
 
Have you grounded the PCB's ?

99% of computer PSU's ground the pcb's via the chassis it's bolted to.Make sure all the mount holes are a) connected to a metal chassis , and b) that the chassis is properly grounded.

The interference you describe : some of it is probably EM interference from the switching portion of the PSU......only way to stop it is to put the psu in a faraday cage type assembly ( a metal box)....but some of it could be ground loop problems.Most 'audio hum' is ground loop related.....best way to fix this : 'Ground loop isolator' from radio shack 20$.

:D
 
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