hardware bug ethernet/hdmi?

[RaspLearner]

A peculiar thing happened to me, recently, while tinkering with the raspberry Pi (model B, 512 MB). All my former tries (mainly with raspbmc and open elec) were going reasonably well, while I was using the composite-video/audio jacks connected to a TV. To see how it looked, but mainly because my computer-screen didn't have HDMI. In the end, however, it was time for some other things to try out, and I was planning on trying to make it into a lightweight webserver (probably with lighttpd) and so I decided to install raspbian, latest version. Instalment worked just fine, but to get something on my screen, I bought a hdmi-to-dvi adapter. I plugged everything in, booted it up, and...got nothing.

I first thought maybe it was just borked or badly installed after all, but then suddenly the screen flickered, showed me the working raspbian OS, then disappeared again, only to appear for a few seconds (with lots of 'stripes' and visual noise) and then to turn black again...intermittently, varying in seconds to minutes.

Clearly, it was unstable as hell. I thought maybe it was the adapter, so I tried it out with other stuff, but there it seemed to work well. I checked all my connections to make sure it wasn't due to a bad connection somewhere, and tried some other things - all to no avail.

In the end, I thought maybe an update would maybe help (though it was clearly a hardware problem, but heck, one gets desperate after hours of fruitless searching). *THE MOMENT* I put the ethernet-cable (a regular cat5) into its socket however, my screen got a stable, crispy clear image. Mind you, without updating anything, just by putting it in. And everything worked just fine (and was showing).

I removed it...it went black with now and then a flickering, again. I put it in: clean, stable image again. Thus, it clearly has to do with the hardware, but I can't imagine what, because surely, the ethernet-cable has nothing to do with the hdmi video-output. Or at least, it shouldn't have. but I guess some kind of interference (which, in this case, makes it better?) is there, otherwise it's inexplicable. Maybe some small current-loop or whatever is passing through (or inhibiting) to my ethernet when connecting, and has an influence on the hdmi-socket/port? Some sort of hardware bug seems a reasonable assumption, since I hardly think it was a feature that hdmi only works correctly when the ethernet-cable is plugged in(?).

Anyone had this experience too? Any other suggestions why this occurs?

[mahjongg]

Sounds like a grounding problem, without any cable (but power) plugged in the PI isn't connected to earth in any way. Normally that isn't a problem though.

[rpdom]

Sounds like a grounding problem, without any cable (but power) plugged in the PI isn't connected to earth in any way. Normally that isn't a problem though.

I'd agree with this.

However the ethernet cable is totally isolated from ground and everything else through the transformers in the socket - unless the cable is shielded and most cat5 cable isn't.

It must be something else.

Very odd.

[drgeoff]

Try increasing the hdmi drive as per http://elinux.org/R-Pi_Troubleshooting# ... VI_monitor

(BTW there is no S-video from the RPi. Hence the second line of your first post in this topic is confusing.)

[mahjongg]

Sounds like a grounding problem, without any cable (but power) plugged in the PI isn't connected to earth in any way. Normally that isn't a problem though.

I'd agree with this.

However the ethernet cable is totally isolated from ground and everything else through the transformers in the socket - unless the cable is shielded and most cat5 cable isn't.

It must be something else.

Very odd.

No, not exactly, inside the connector the four unused lines of the RJ-45 connector, and center taps of the ethernet transformers (secondary side) are connected to 75 Ohm resistors, which on the other end are all connected together and, (typically) through a 4 Kilovolt 100nF connected to the GND of the device. As in this picture:

So for AC the ethernet cable isn't an isolation, at least not if the other end is connected to an ethernet device using the same arrangement.
So its still possible that for AC a more or less low-ohmic path to earth may be created when the ethernet connector is plugged in.

[RaspLearner]

Try increasing the hdmi drive as per http://elinux.org/R-Pi_Troubleshooting# ... VI_monitor

(BTW there is no S-video from the RPi. Hence the second line of your first post in this topic is confusing.)

I meant the Composite RCA. Didn't notice the error, will correct it.

Sounds like a grounding problem, without any cable (but power) plugged in the PI isn't connected to earth in any way. Normally that isn't a problem though.

I'd agree with this.

However the ethernet cable is totally isolated from ground and everything else through the transformers in the socket - unless the cable is shielded and most cat5 cable isn't.

It must be something else.

Very odd.

No, not exactly, inside the connector the four unused lines of the RJ-45 connector, and center taps of the ethernet transformers (secondary side) are connected to 75 Ohm resistors, which on the other end are all connected together and, (typically) through a 4 Kilovolt 100nF connected to the GND of the device. As in this picture:

So for AC the ethernet cable isn't an isolation, at least not if the other end is connected to an ethernet device using the same arrangement.
So its still possible that for AC a more or less low-ohmic path to earth may be created when the ethernet connector is plugged in.

Grounding is probably the cause indeed. When I disconnect the cable from my router, it goes black again (or sporadic 'views'). When I use another cable, the screen remains black. Even if I put the same cable into another port/slot in my router, it doesn't work. Seems to be very specific, thus.

As an aside, I've successfully managed to install a working webserver on it (lighttpd), and though I know many have gone before me in this small endeavour, I still feel rather satisfied with myself. ;-p

[RaspLearner]

Try increasing the hdmi drive as per http://elinux.org/R-Pi_Troubleshooting# ... VI_monitor

(BTW there is no S-video from the RPi. Hence the second line of your first post in this topic is confusing.)

I tried what you (your link) suggested, but it didn't help. I first thought you nailed it and it was due to that, but... just didn't work, even though my hdmi cable is pretty short. I went as far as to set it at 10, even (they recommended 4, so I tried everything from 4 to 10). But every time I took out the ethernet-cable, it went blank.

Even weirder: I've noted that it goes blank even if I change the ethernet-cable next to it (to the right) of where the actually cable is put in the router. There must be something going on with those ports of the router or those cables. But somehow, I can't complain, because without it, I wouldn't be able to do squat.

Hmmm... it could still be due to the hdmi-dvi adapter (loss of signal), but if it's not...can I return the raspberry Pi as faulty while it remains in guarantee, and get a new one, or a repaired one?

[mahjongg]

stupid question. are you sure you entered the HDMI connector into the PI all the way?

p.s. by "raspbian" I assume you mean the PI? raspbian is the OS.

[drgeoff]

Hmmm... it could still be due to the hdmi-dvi adapter (loss of signal), but if it's not...can I return the raspbian as faulty while it remains in guarantee, and get a new one, or a repaired one?

I think it is more likely that your HDMI cable or HDMI to DVI adapter is the culprit. Can you beg/borrow/steal alternatives to try? Or temporarily take your kit to somewhere with a display with an HDMI input.

[RaspLearner]

stupid question. are you sure you entered the HDMI connector into the PI all the way?

p.s. by "raspbian" I assume you mean the PI? raspbian is the OS.

Yes, I checked the cables from the start of the problem, as I've said.

Yes, I know raspbian is the OS. You assume correctly; I meant the raspberry Pi. It has to do with the hardware, after all, not the software.

My thought on it for the moment, though, is that it's probably rather due to signal loss or whatever from the fact that I used a simple and rather inexpensive hdmi-to-dvi adapter. If it would be a manufacture issue of grounding with the hardware of the PI, I think the problem would have surfaced en masse far sooner. I think the most logical next step, is to see if I still get the same when I connect it directly to a screen with hdmi. Though I'm not sure how any signal could get better by pluging in an ethernet cable, so the grounding must have *something* to do with it.

It's still a bit annoying that I have to keep the ethernetcable plugged in to see anything, but I'll manage somehow, for the time being. It worked for installing lighttpd, after all. It will become a bit problematic if I'm done with various tinkering, and want to use it as media-player, though.

Edit: I could also buy the PI-VIEW HDMI to VGA Adapter Cable, ofcourse, and see how that pans out. Though...if I'm going to put all things together I've bought for the Pi to get it working the way I imagined it, I'm guessing I'm over 100 euro by now, instead of the original 35 euro. But ah well, it's not the end of the world neither.

[mahjongg]

why not (if grounding is the problem) ground your monitor!

[RaspLearner]

why not (if grounding is the problem) ground your monitor!

Shouldn't that automatically be the case, when it's connected with a three-pin (current)cable? And if not; how to do that safely/easy?

[mahjongg]

that should be the case, if you plugged your TV into a grounded socket.

If not I expect that about half your AC mains voltage (that is 55V if your mains is 110V, or 120V if your mains is 240V) is on the whole PI device, relative to GND!

That, because most large electronic equipment has filter capacitors in their power supply on between both mains pins, and the ground pin. Without an actual GND it means these capacitors split the AC in half that is between the hot and cold poles of your mains, and that half mains voltage is connected to the GND of the TV, and thus the PI.

Most often all water pipes in a house are properly grounded, you could try measuring with a digital multimeter set to AC Voltage between the PI's GND and the nearest water tap, or central heating radiator, or something similar.

[Burngate]

Most often all water pipes in a house are properly grounded ...

Unless they're plastic - and modern water mains in the street are often plastic, so even copper pipes in a house aren't necessarily properly (low impedance) grounded

[mahjongg]

Well, even if they are plastic, water is conductive, so that filled with water they form a tract to earth that is still low impedance enough for this measurement! Even if the connection is a few dozen kilo ohm you should still measure a considerable voltage.

Anyway, in most places where I have seen a water line enter the house, going into a copper pipe, that pipe was grounded at that point, I think it has to be a building safety rule or something, but maybe that is only so in the Netherlands.

Tell you what,if the house has a lightening rod, connect a wire to its ground spike, that should be ground enough for most purposes.

[rpdom]

I believe that in the UK it is a requirement that the copper piping on the cold water supply to the house is connected to a good ground - even if the pipe coming into the house is plastic.

For some reason hot water pipes are not supposed to be used as ground.

A quick check under my kitchen sink confirms that all the copper pipes under there, and the metal sink itself, are all connected to ground wires.