On Sun, 26 Feb 2012 09:28:53 -0500 Greg Troxel <[email protected]> wrote:
> > Attila Kinali <[email protected]> writes: > > > I finally got around to measure the internal supply pins of my > > net5501 to see what exactly is going on. What i see are very very > > short (<1us) drops of the 12 down that are larger than 1V. I guess > > the drops of the 3.3V and 5V supply that i see at the same time > > come from the 12V drop. But with the measurement equipment i have > > here and the lack of schmeatics, i cannot be sure. (it could be the > > other way as well) > > You could try putting a capacitor across the supply. 1us duration drops > of more than 1V sound pretty suspicious though that something in the > output filtering of your supply is messed up. Did that already. Put two 1000uF capacitors on J5 over 3.3V and 5V. It didn't help. Using my 16V supply i got rid of those deep spikes, now the 16V was stable. But the 3.3V showed still 50mV spikes. Unfortunately, with the equipment here i can not asses whether these spikes could lead to any trouble or not (using a low cost Tek 2024B isn't going to say much about such transients). The only fact i can be sure of ia that something is causing the net5501 crash under load. And i'd like to know what it is. > It could also be that something is drawing outrageous currents at 3.3V which > is stressing the regulator's current-handling ability and this is > appearing upstream. But that seems less likely than a supply with > something wrong (a bad output filtering cap, perhaps). Well, with no specs what the on board power supplies can handle, i have no way of telling whether something could be drawing too much current. The inductors look like they can take 1-2A each.. maybe more. I'm a little bit surprised, that i couldnt see any ceramic capacitors to block the HF noise. But i didn't look on the bottom, so... > I have a hard time believing that a supply that will provide 12V 3A > would have trouble. But I can believe that a particular supply labeled > 12V 3A would not actually provide that reliably. Oh, that's quite easy to explain. Those power supplies sold by soekris (and many others) are cheap stuff. They are made to be cheap, not reliable. They can deliver nice continous power, but the moment you have load transients they behave badly. That's not the fault of soekris, it's just how power supplies are these days. And the only way to handle this is to make sure your system can cope with sudden power supply drops (unless you want to spend 3 to 10 times as much for the power supply). > I'm not soekris, obviously, but my limited understanding is > > the net5501 only uses 5V and lower, actually Yes > the disk connector is a notebook disk, which is at most a 5V device Nope. Notebook HDs still use 12V for the motor. > same with PCI PCI supplies +3.3V, +5V, +12V and -12V. At least the net4501's manual states that the +12V and -12V supplies are not provieded, but there is no such statment for the 5501 (btw: that makes the PCI connector of the 4501 non-conformant to the PCI standard, but that's probably ok for most cards these days). > There is a regulator (perhaps a 7805) that brings 12V down to 5V. One > can jumper to not use the regulator, and then the input has to be > exactly 5V. No, there are no linear regulators on the net5501 for the 5V and 3.3V. My guess is that the LM2642 that is halfway between the power socket and the big inductors provides those two power rails. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? _______________________________________________ Soekris-tech mailing list [email protected] http://lists.soekris.com/mailman/listinfo/soekris-tech
