Replacing the Power Supply

[jonsmith]

Hoping you can help with a question I have...

Having replaced my hard drive with a CF card and replaced the CPU fan with an ultra-quiet model, I'm now looking to replace the actual power supply, as it's the last noise-making part of my d8b. I already have a spare low noise ATX supply and I understand that I'll need to add an additional momentary switch to get this to turn on. Where I am stuck is to do with the second (non-standard) set of cables that come out of the currently installed power supply. These all seem to lead to a board consisting mainly of fuses and the other cables on this board run to the front power switch. What does this board actually do? Not having these cables on the ATX supply, is there a way of replicating/bypassing what those cables do?

In the database, there is a description by Steve Hammond as to how he replaced the supply but I don't understand exactly what he did with this part. I've tried to follow the link to PM him for more details, but it doesn't work. Has anybody else done this who can help me?

Thanks very much.

Jon

[synthjoe]

Welcome to the forum, Jon!

Those are the mains 'inlet' wires. From the IEC socket on the ATX PSU mains voltage should not go to the inside of the PSU (as it is the case with regular POC PSU's) but directly to the board you've pinpointed, via the cable (2 conductors). Then it goes through the front mains switch and feeds the other two PSU units and returns to the inside of the ATX PSU, as well (via the other two conductors). The remaining fifth wire (green-yellow) is the safety ground (housing/third prong of the IEC connector).

Hope I managed to clarify rather than the opposite.
If you use the same cabling and fit it with the new ATX PSU, then you might as well just short the soft power button to 0V (black wires) and it will switch on automatically when the front mains switch is on.

[jonsmith]

Thanks.

Yes, I think that's a great help. So I need to open up the ATX supply and run the mains out to the 'fuse board' then back into the supply? In the ATX supply, there's blue/brown coming off the IEC PCB to the main PSU board, so I'm assuming I can remove those links and from IEC board (white/black) to the 'fuse board' first, then back from the 'fuse board' to the main board on the ATX supply (blue/brown)?

Thanks again for your help.

[synthjoe]

Yep, something like that. Or rather: exactly like that. Given that the d8b has three PSU's inside the CPU box and only one mains inlet, you'll need some wires anyways to get the juice through to the other two. Since you're there already, you might as well run the ATX wire back from the fuse board exactly as you've described and voilá: you can leave out the extra switch for the ATX PSU.

[anyhorizon]

I'm perplexed as to what the problem is in terms of power supply noise. The only thing that makes noise in there is the fan and that's an easy replacement option.

Peter

[FrankH]

'm perplexed as to what the problem is in terms of power supply noise.

I think Synthjoe explains this in detail in the Channel Noise Floor thread. Audio noise...not mechanical.

[jonsmith]

My main focus was mechanical noise. OK, I could change the PSU fan, but a small fan as found on the installed supply has to spin fast to shift air (generally = more noise) & there are now power supplies around that are significantly quieter (in fact almost silent), due to design improvements. The power supply is by far the noisiest part of the box, now that I've replaced all the other noise-generating parts. I know that this ATX supply I have is significantly quieter, more efficient, most likely has a more stable output and will probably last a few years longer than the one currently installed.

As it happens, having taken the existing PSU apart to examine the internal wiring, on reassembly it is actually quieter than before, so I'm assuming something had worked loose over time and was vibrating. However it is still noisier than my spare ATX one & I'm sure it will die one day - I'd like to at least know how to replace it with a better model if this is possible (and others seem to say that it is).

Any subsequent improvement in audio noise would be a bonus!

Thanks for your help folks.