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Author Topic: PCI-E Extenders all bad? Lots of problems.  (Read 9401 times)
sveetsnelda
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September 20, 2011, 04:26:18 AM
 #21

I forgot to post this quite a while back, but I should have.  I'm surprised that I haven't heard this mentioned anywhere else, but I had a similar problem that took a little time to figure out.

Backstory -- When I first started putting together my first mining rigs, I noticed that some cards were performing slightly better than others.  Card performance varied anywhere from 1 to 4 percent.  It didn't make any sense.  I had 32 identical cards that had the same clock rates, so the performance should be nearly identical between cards.  At the time, I was using separate instances of Phoenix for each card instead of a combined miner, so I could see the hash rate discrepancies.

Long story short, I noticed that the cards connected directly to the board never varied...  only the cards with 1x risers did.  My rigs have 4 cards each -- 2 in the board and 2 connected with risers.  I then noticed that the hash rate in Phoenix would fluctuate when I moved the riser cable around.  Yep...  the risers easily pick up EMI from nearby components.

Since PCI Express runs at such a high frequency, it's extremely susceptible to interference over long distances.  You'll notice that most of the "name brand" risers are shielded (like this one http://www.newegg.com/Product/Product.aspx?Item=N82E16815158290).  They're shielded for a reason.

With every miner I assembled, I sat and watched Phoenix while moving the cable around until I hit the max hash rate (and then left them there).  However, I had cards that would stop mining randomly.  Sometimes they would mine for a few hours, sometimes 1/2 of a day, and sometimes days without hanging.  When they would hang, it didn't take anything more than restarting the miner.

I started logging these hangs over the course of a week or so.  I noted which machines would hang and which cards it happened to.  Of course, it always happened to the cards with the risers.

Here's what I did to fix it.  I bought a roll of aluminum duct tape and shielded the cables myself.  Be very careful with this though -- aluminum is very conductive.  If you're afraid of them touching against your components *wrap them in electrical tape* after applying the aluminum tape.  I'm sure you could use aluminum foil to shield them too, but I'd recommend the tape if you have very many risers to wrap.

After doing this, I *rarely* get a miner that hangs.  With 54 video cards mining 24/7, I only have to restart a miner about once every week or two.  It rarely happens.  Here's the exact tape that I used, but I'm sure that just about any aluminum foil will do the job.  http://www.amazon.com/Nashua-324A-Cold-Weather-Premium/dp/B0015V93KG.  I bought it at Home Depot.

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September 20, 2011, 05:02:51 AM
 #22

Great find, aluminum tape is so useful Smiley

Will definitely be giving this a try.

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September 20, 2011, 12:06:34 PM
 #23

I forgot to post this quite a while back, but I should have.  I'm surprised that I haven't heard this mentioned anywhere else, but I had a similar problem that took a little time to figure out.

Backstory -- When I first started putting together my first mining rigs, I noticed that some cards were performing slightly better than others.  Card performance varied anywhere from 1 to 4 percent.  It didn't make any sense.  I had 32 identical cards that had the same clock rates, so the performance should be nearly identical between cards.  At the time, I was using separate instances of Phoenix for each card instead of a combined miner, so I could see the hash rate discrepancies.

Long story short, I noticed that the cards connected directly to the board never varied...  only the cards with 1x risers did.  My rigs have 4 cards each -- 2 in the board and 2 connected with risers.  I then noticed that the hash rate in Phoenix would fluctuate when I moved the riser cable around.  Yep...  the risers easily pick up EMI from nearby components.

Since PCI Express runs at such a high frequency, it's extremely susceptible to interference over long distances.  You'll notice that most of the "name brand" risers are shielded (like this one http://www.newegg.com/Product/Product.aspx?Item=N82E16815158290).  They're shielded for a reason.

With every miner I assembled, I sat and watched Phoenix while moving the cable around until I hit the max hash rate (and then left them there).  However, I had cards that would stop mining randomly.  Sometimes they would mine for a few hours, sometimes 1/2 of a day, and sometimes days without hanging.  When they would hang, it didn't take anything more than restarting the miner.

I started logging these hangs over the course of a week or so.  I noted which machines would hang and which cards it happened to.  Of course, it always happened to the cards with the risers.

Here's what I did to fix it.  I bought a roll of aluminum duct tape and shielded the cables myself.  Be very careful with this though -- aluminum is very conductive.  If you're afraid of them touching against your components *wrap them in electrical tape* after applying the aluminum tape.  I'm sure you could use aluminum foil to shield them too, but I'd recommend the tape if you have very many risers to wrap.

After doing this, I *rarely* get a miner that hangs.  With 54 video cards mining 24/7, I only have to restart a miner about once every week or two.  It rarely happens.  Here's the exact tape that I used, but I'm sure that just about any aluminum foil will do the job.  http://www.amazon.com/Nashua-324A-Cold-Weather-Premium/dp/B0015V93KG.  I bought it at Home Depot.

Man, nice one. Thats it! With 4 5850's on each rig i noticed with 4 cards connected i the one in the main slot has to be clocked down a little over the others. Im using £3 cables and added my own molex power (£15+ is just a joke, by anyones standards) but no shielding. I have LOADS of aliminium tape about also. I will be doing this promptly Smiley Nice find Smiley
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September 21, 2011, 04:42:45 AM
 #24

In 3 months I have had no problems with my 9mart x16 extenders.  Currently I am using 8 of the 10 I bought.  I added Molex power to a couple of them myself since I am running 5 cards/rig.  Once or twice there was an issue with the miner not starting but it was because I had bumped a cable, re-seating the connector solved the problem both times.  Be careful that your cables are not rubbing on the PCB of the neighboring video card, I can see that as being an EMI source as well as a potential short if the fan vibration/heat wears through the insulation.
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September 28, 2011, 03:08:45 AM
 #25

In 3 months I have had no problems with my 9mart x16 extenders.  Currently I am using 8 of the 10 I bought.  I added Molex power to a couple of them myself since I am running 5 cards/rig.  Once or twice there was an issue with the miner not starting but it was because I had bumped a cable, re-seating the connector solved the problem both times.  Be careful that your cables are not rubbing on the PCB of the neighboring video card, I can see that as being an EMI source as well as a potential short if the fan vibration/heat wears through the insulation.
I haven't had any problems with the x16 extenders...  only the x1.  I have six 9mart x16 extenders and they have been just fine.  I'm guessing with PCI-E's ECC and the additional bandwidth through the cable, it's able to deal with the interference.  Just a guess though.  I've only had to worry about wrapping my 1x extenders, and I've had to do it with every rig to prevent the random miner hangs.

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September 29, 2011, 01:45:28 AM
 #26

I'll be moving my rigs to the other side of the room this weekend...
going to vent all the hot air into the cold air duct instead of outside

[edit] had a power failur and just wanted to save this post before PC died...
anyways...
when i reset up my miners i'll be putting on the tape to make sure all is good.
curretnly i have each cable seperated by a piece of wood so that they don't touch
sveetsnelda
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September 30, 2011, 02:14:42 AM
 #27

when i reset up my miners i'll be putting on the tape to make sure all is good.
curretnly i have each cable seperated by a piece of wood so that they don't touch
A piece of wood between each cable is enough to block EMI at those frequencies...  However, that would only block EMI between cables.  If there's nothing else near the cables, you're probably fine.  My problems were more pronounced because a lot of my miners had extenders running between cards that were physically plugged into the board.  However, I've experienced this problem on a rig with 4 cards *all* on risers.  They probably got their EMI from each other's riser cables being close to each other.  The tape took care of it though.

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October 02, 2011, 11:31:03 PM
 #28

Quick Question...
when I wrap the PCIE cables with metal tape...
do I wrap them up with a layer in between the cables?
or just around them?
sveetsnelda
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October 03, 2011, 01:04:34 AM
 #29

I wrapped between them (and then around), but it's most important that you wrap around them to keep external EMI out.

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October 03, 2011, 02:23:12 AM
 #30

I wrapped between them (and then around), but it's most important that you wrap around them to keep external EMI out.

I wrapped around 2 of them then i came across the idea to wrap between them
so i thought i would ask.
unfortunately I'm now to inebriated to do the task on hand...
so it will have to wait till tomorrow
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April 11, 2013, 09:42:46 PM
 #31

I've got an Asus P5B-Deluxe (LGA 775 with 2x PCI-e X16). Can I add a riser and newer card to this? I'm thinking I can add two! Smiley

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April 12, 2013, 08:19:23 AM
 #32

Got a http://www.amazon.com/gp/product/B004XD74MC for $9 and it works perfectly... excepting that every time I restart my computer it only displays a blinking dos curser and doesn't start up unless I replug it in. But its those little quirks and flaws that keep a guy interested!

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