As in any project involving electronics, safety procedures must be followed at all times. It is recommended that you have some electronics experience before attempting this mod. Assess the potential risks, which could entail death by electrocution, and base your decision to try this mod accordingly.
Always disconnect power sources before working on electrical equipment. Ensure that residual charges are no longer present before working on any equipment. Always wear safety glasses when doing any electrical work, especially when soldering. Be safe, not sorry.
I recently fried my T-bird 1GHz processor by chipping the core. To replace this chip, I bought a T-bird 1.4 GHz for a quick replacement to get my machine back up and running. I hadn’t opted for the XP series, because with my motherboard, the IWill KK-266-R, compatibility with the Athlon XP series CPU is marginal. As some of you may already know, this chip draws more current than any other Athlon series CPU. So began my problems.
The PSU I’ve been using in this rig is the one that came with the case – a generic, 300 watt ‘Green Tech Brand’ power supply. I’d been using this PSU with a heavy load – (3) 7200rpm Hard Drives, a 52x CD Drive, A Voodoo 3 Video Card, NIC, and winmodem. My 5V line on my PSU was already suffering with the 1 GHz chip, although it had caused no problems with lockups or instability. It should be noted that all components are being run at stock speeds and voltages, no overclocking has been done.
After installation of the new 1.4 chip, I began to have random lockups, getting a normal runtime of about 12-20 hours before the machine would crash. Running any sort of graphics intensive application crashed the system in a matter of minutes. Assuming at first that the -very- cheap HSF I was using (identical to the AMD retail HSF) wasn’t cooling the processor well enough, so I checked out MBM5 readings.
They read in at 44C, not cool, but shouldn’t be causing any problems at stock speeds. So I ran through the rest of MBM, checking Fan RPMs, Voltages, etc. I was instantly drawn to the +5V reading: 4.63 Volts! It was amazing that the system was even running at all! I checked a 4 pin Molex with my multimeter, reading the +5V at 4.82 volts, unacceptable by anyone’s standards, especially owners of power-hungry AMD chips. Something had to be done.
The obvious fix would be to buy a new PSU, but I was pretty tight on cash at the time. As everyone knows, a budget breeds creativity and innovation on the cheap.
I knew that Hoot’s 5V Mod would be necessary, seeing an almost 0.2V difference between the Molex pins and the MBM reading. I still needed to raise that +5V line another 0.2V, but how?
For this extra voltage, I turned to the 12V line.
In practice, the 12V line of a PSU is used mainly for powering relatively insensitive devices: HD motors, CD spindles, fans etc. The +5V line needs precise voltage regulation. So I stole some power from my +12V to feed the hungry +5V devices.
To do this, I have used a couple of 7805 linear regulator ICs. These devices are precision linear regulators, which can take an input voltage from 8-40 volts and step it down to 5V, dissipating the extra voltage as heat – hence the term ‘linear’. They are 3 pin devices, packaged in a common TO-220 IC case. Each of the three pins, from left to right looking at the front (The side with the writing, pins facing down) are Vin, Ground, and Vout.
Each one of these ICs, properly cooled, can source a maximum of 1A @ 5V. They are internally current limited and thermally protected, so they make good supplements to the existing 5V line; they cannot be overdrawn. The costs locally for these are $0.45. Heatsinks run anywhere from $0.50 to $2, depending on how large you get.
I used cheapy Heatsinks on my project, just a few I had laying around. (I do not suggest using ‘stamped tin’ type Heatsinks – they can handle nowhere near the load of a 7805. I suggest at a minimum nice aluminum Heatsinks, about 1″ long)
By soldering two of these in parallel and zip-tying them to my ATX motherboard power header, I had a nice compact addition to my PSU. Vin connects to the yellow power wire, Ground to any black power wire, and Vout to any red power wire.
I also connected Hoot’s 5V mod to Vout, running this wire straight to the 3 MOSFETs on the motherboard. These 7805s get VERY hot, so good cooling, whether it be large passive Heatsinks or an actively cooled setup, is a must.
My passive setup has been running fine. There is a good possibility that these produce enough heat to increase your case temps, so beware.
I used two to increase my +5V line because I wanted to be good and sure there would be enough power there to raise it to an acceptable level. You could use anywhere from one to an infinite amount of 7805s, but be aware of how much current you’re pulling away from the 12V…
Upon the first boot, BIOS read my +5V line at a perfect 5.0V. After booting into Windows, MBM read out at 4.95 volts. To date, the 5V line voltage varies independent of load and ranges from 4.91 to 4.95 volts, sitting most of the time right at 4.93 Volts.
The 12V line remained unaffected, at 12.16 volts in MBM. Real world measuring with the multimeter indicated the +5V at 4.94V and the +12V at 11.98V. An otherwise useless PSU has been rejuvenated to fight yet another day, at less expense than a floppy drive cable. May your 5V line live long and prosper.
There is a forum thread covering this topic on the Overclockers.com forums, it can be found HERE.
On the thread, there has been a suggestion of using an adjustable linear voltage regulator, such as an LM317, as an alternative to the 7805, providing the user an adjustable source of 5V supplementation. It would be rather easy to implement this idea at only slightly more complication and expense. This would give you even greater control of your 5V line.
Here are a few pictures better detailing how my particular project turned out:
This shows the devices after they’ve been attached. The red wire ‘tail’ running off the bottom of the picture connects to Hoot’s 5V mod on the motherboard.
This is how I spliced the wires into the ATX connector.
Hoot’s 5V mod, applied to my KK266-R RAID motherboard.
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Tags: Systems & Components