PC Monitors switching off and DVI to HDMI cables failing

Please do not be put off by DZ - he comes in at the end of a stressful day sometimes and it shows - it is not just you  - he is like that with the rest of us too.

(now I shall have to duck...)


Right, well you have been a busy bee. Thanks for all that hard work. Digital persist is jolly useful on a scope isn't it?


What follows may be complete hogwash, it is as they say 'your party'. However, here is how it feels to me, having read it.

I think we should assume for now probably only really borking leads with electronics in, and the IT folk who had hold of it before you are either not remembering it right when they tell you, or they were special HDMI leads that had frame rate converters in or something, but in any case were not simple passive.

Display port - ah yes a right pain in the interface being 3V logic, when DVI and HDMI are 5V. Expensive if the level shifters are omitted in the cheap far eastern model


I had not clocked immediately that the clean and dirty rings were 2 phases on the same DB, so two lives and a common neutral.


That opens the door to a fun test. IF they can be swapped at the breaker, does the problem also swap to the other side of the room, or safer, if moved both to the clean phase, does the problem go away ?

I.e. have you really got one dirty phase coming into the board? I suspect you have something like that, but it is hard to prove. If the sub-main feeding the DB is SWA or waveform, then it forms a kind of coax transmission line, so spikes can be conducted in from quite a distance away without much attenuation.


The short duration transients may be partly radiated - faster then about a microsecond risetime, (well for wiring of tens of metres long) and it is often as easy  or easier for the energy to get off the wire and back on again further down in a radio and antennas or even a loosely guided wave sort of way rather than in a purely conducted way.

I suspect your remote light switch may be re-creating a version of  the famous experiment of Heinrich Herz    but with the scope serving as a rather more sensitive detector than Herz's original spark gap.


So, what to do? Well first stop plugging in and flashing lights ;-)

More seriously, it seems there are fast spikes coming in on the second phase, so some sort of filtering at the DB may be worth installing, of the kind that puts quite some capacitance from L to E and N to E, to absorb any fast rising edges inbound, Verify that the  N voltage is not moving relative to the lives, by looking at the NE waveform on the scope at the DB, or as near as you dare get to it,  You may care to beef up the earthing. Threading some ferrite on the inbound cables will have no ill effect on the 50Hz, but will raise the series impedance to provide opposition to microsecond scale stuff. (example)


There is one other possibility to be eliminated - and that is one of the loads on the dirty ring is acting as the impulse generator, perhaps with partial 'crackly'  break down of a varistor or internal filter capacitance inside the PSU in one PC or the other when it warms up. Or a scratchy current carrying contact in a plug, socket or mains lead. This would be the suspect if the swap phase test brings the problem with it..


I assume you would have mentioned other details like metal suspended ceilings or floors, but if there are then these are possible re-radiators.




Mike.

Edit do not be upset by the phase inversion - the scope will trigger on both positive and negative edges, and a sine wave with some zero-crossing distortion that includes an occasional 'twitch' or reversal of direction may cause it to trigger on a short up ring during a down edge, so it appears to fire on  the wrong edge occasionally, and the persist on the scope makes it look really weird.

Traces with fuzz riding on them like the chairs on a ski-lift are hard for the scope to get a grip on, even a modern digital one.

Please do not be put off by DZ - he comes in at the end of a stressful day sometimes and it shows - it is not just you  - he is like that with the rest of us too.

(now I shall have to duck...)


Right, well you have been a busy bee. Thanks for all that hard work. Digital persist is jolly useful on a scope isn't it?


What follows may be complete hogwash, it is as they say 'your party'. However, here is how it feels to me, having read it.

I think we should assume for now probably only really borking leads with electronics in, and the IT folk who had hold of it before you are either not remembering it right when they tell you, or they were special HDMI leads that had frame rate converters in or something, but in any case were not simple passive.

Display port - ah yes a right pain in the interface being 3V logic, when DVI and HDMI are 5V. Expensive if the level shifters are omitted in the cheap far eastern model


I had not clocked immediately that the clean and dirty rings were 2 phases on the same DB, so two lives and a common neutral.


That opens the door to a fun test. IF they can be swapped at the breaker, does the problem also swap to the other side of the room, or safer, if moved both to the clean phase, does the problem go away ?

I.e. have you really got one dirty phase coming into the board? I suspect you have something like that, but it is hard to prove. If the sub-main feeding the DB is SWA or waveform, then it forms a kind of coax transmission line, so spikes can be conducted in from quite a distance away without much attenuation.


The short duration transients may be partly radiated - faster then about a microsecond risetime, (well for wiring of tens of metres long) and it is often as easy  or easier for the energy to get off the wire and back on again further down in a radio and antennas or even a loosely guided wave sort of way rather than in a purely conducted way.

I suspect your remote light switch may be re-creating a version of  the famous experiment of Heinrich Herz    but with the scope serving as a rather more sensitive detector than Herz's original spark gap.


So, what to do? Well first stop plugging in and flashing lights ;-)

More seriously, it seems there are fast spikes coming in on the second phase, so some sort of filtering at the DB may be worth installing, of the kind that puts quite some capacitance from L to E and N to E, to absorb any fast rising edges inbound, Verify that the  N voltage is not moving relative to the lives, by looking at the NE waveform on the scope at the DB, or as near as you dare get to it,  You may care to beef up the earthing. Threading some ferrite on the inbound cables will have no ill effect on the 50Hz, but will raise the series impedance to provide opposition to microsecond scale stuff. (example)


There is one other possibility to be eliminated - and that is one of the loads on the dirty ring is acting as the impulse generator, perhaps with partial 'crackly'  break down of a varistor or internal filter capacitance inside the PSU in one PC or the other when it warms up. Or a scratchy current carrying contact in a plug, socket or mains lead. This would be the suspect if the swap phase test brings the problem with it..


I assume you would have mentioned other details like metal suspended ceilings or floors, but if there are then these are possible re-radiators.




Mike.

Edit do not be upset by the phase inversion - the scope will trigger on both positive and negative edges, and a sine wave with some zero-crossing distortion that includes an occasional 'twitch' or reversal of direction may cause it to trigger on a short up ring during a down edge, so it appears to fire on  the wrong edge occasionally, and the persist on the scope makes it look really weird.

Traces with fuzz riding on them like the chairs on a ski-lift are hard for the scope to get a grip on, even a modern digital one.