OCZ GameXStream OCZGXS600 (600W) and OCZGXS700 (700W)

I reviewed power supplies from OCZ twice in my articles. Those were ModStream and PowerStream series, both manufactured for OCZ by Topower. With the release of its new GameXStream series OCZ decided to change its supplier. Both these PSUs are manufactured by FSP Group. This is obvious even from the label. There’s only a different manufacturer name on it in comparison with FSP’s own Epsilon that we have tested in our labs, too.

Below I will describe the two models, 600W and 700W, together since they are based on the same platform and do not differ much from each other.

The internal design of the PSUs is typical of FSP’s new series and is first of all remarkable for its small heatsinks. As I wrote earlier, it had become possible due to increased efficiency of the PSU. Particularly, they make uncommon (in comparison with other PSUs) use of diode packs. One 30A pack is usually installed to provide a 30A current, but in new PSUs from FSP they connect two packs in parallel. Why if each of them can ensure the required 30A? Because the voltage drop on diodes depends non-linearly on the passing current. So, two packs through each of which a current of 15A is passing generate less heat than one pack with a 30A current. This is the reason why there are so many components on the heatsinks of this GameXStream PSU. Three heatsinks even had to be used because the engineers couldn’t have accommodated all the components on only two of them.

On one hand, this approach increases the cost of the semiconductor PSU components, but the cost of the heatsinks is lowered. FSP’s engineers must have achieved a positive overall effect with that solution.

Switching power supplies – any switching power supplies – cannot work under zero load because the energy accumulated in the inductances of the PSU’s output circuits (in the transformer or choke, depending on the topology employed) doesn’t go into the load, which results in an uncontrollable growth of voltage on the PSU output. The ATX standard, however, requires that the PSU be able to start up without external load, and the manufacturers used to install resistors that provided the necessary minimum of load. Such PSUs worked normally and yielded stable voltages even if nothing at all was connected to them.

Lately, those resistors have been abandoned as the manufacturers are trying to improve the efficiency of their products. Of course, the resistors dissipate little power, but this is still considerable when the PSU is under minimum load. Another problem rose up as a consequence. New PSUs would not start up with some mainboards, those that didn’t provide some minimum load right after the start. As a result, the PSU that didn’t have its own internal load would not operate correctly or would not send the Power OK signal to the mainboard.

To avoid this problem, FSP engineers implemented a “smart” internal load that works only for the first few seconds on your turning the PSU on. It is located on a separate small card (see the photograph above) and consists of two clusters of pull-up resistors, two transistors that connect those clusters to the +5V and +12V circuits, and an RC circuit that keeps the transistors open for a short interval after the turning on of the PSU. As soon as the RC circuit capacitor is charged up, the transistors close and turn off the pull-up resistors. By this time, the mainboard should have started up successfully, providing an external load on the PSU. This is how simple it is. It’s even strange that PSU manufacturers didn’t come to this solution long ago. The problem of not-starting-up mainboards wouldn’t have occurred then (this problem was reported not only with regards to FSP power supplies, by the way).

However, there can be another problem. The PSU may refuse to start up if you turn it on right after having shut it down. If the capacitor of the RC circuit hasn’t had enough time to get uncharged, the transistors will be open initially. I don’t think that’s much of problem, though. You can just wait for a few minutes and try to turn the PC on again.

The PCBs of both power supplies have a marking that reads “FSP700-80GLC(NEW)” which seems to imply a new revision of the model. Unfortunately, I have no information about the changes (besides the above-described card, but it is separate from the main PCB). Visually, the group voltage regulation choke seems to have become larger. A more detailed examination of the interior of the PSU would be beyond the scope of this review.

The PSU is equipped with the following cables and connectors:

• Mainboard cable with a 20+4 connector (55cm long)
• CPU cable with a 4+4 connector (54cm)
• Two graphics card cables with 6-pin connectors (54cm)
• Two cables with three Molex connectors and one floppy mini-plug on each (51cm from the PSU to the first plug and 19cm more to each next plug)
• Two cables with three SATA power connectors on each (54cm+22cm+22cm)

The cables are all sleeved.

Here’s the label of the senior, 700W unit. The junior model differs from it in having a 100W lower load power both on the +12V rail and in general.

The +12V power rail is “virtually” divided into 18A pieces just as the standard demands. It’s good that the label tells clearly which connector is powered by which line. The wires of the different lines are color-coded in the connectors: yellow for the 12V1 and a combination of yellow with black, blue and green for the other three lines.