Ok, latest update... xD
The boards with only one of the four caps/resistors around the A1, with the alternate other caps...
ISAWHIM,
We appreciate your diagnostic efforts thus far, they have been well documented and thorough. Send back to the two non working boards and we'll you send you another 2 working boards plus an additional 2 non working with issues...
So far, there are three that need to be send back, the one which needs the A1 reworked or replaced. (That was one of the "good ones", the later designs. You would not have seen that chips was out of place, unless you got all personal with the chip like I had. It started running fine, until the heat got to it, I assume. So I am not sure if the inductors or other power components were also hurt. They were all super hot.)
The other two, were the boards which have just stopped responding to detection. (The ones with only the one cap at the A1.) Both have obvious screw-marks across that "COUT46" set of terminals, thus, that was "shorted" at one point in the components operation. Though they were not shorted at the moment I was using them, or running them... I was not sure if that had something to do with the issue those boards were having.
If you could tell me what to look for on those... as they were both once operating perfect. One at 208GHs, and one at 198GHs, prior to just stopping. Those, I believe, had the issue where the boards seemed to start mining faster and faster, just before failure. They eventually started hashing around 50-20GHs, which caused me to re-boot, which would normally seem to "reset" the operational state. But at the time of those cards failures, the "last time they did this", re-booting resulted in the cards just failing to reply for operation.
Are those going to need a component swap? (Thus turning them into the other boards?)
As for the other two boards with the blue heat-sinks... I don't recall any "markings" on those. So, those might work, but may eventually have an issue, as I do recall someone posting "Does anyone have any boards with the blue heat-sinks that is still working". So, that leads me to believe, as well as the fact that they were devoid of heat-sinks, that they will have something to challenge me. xD
Though, I will give those a once-over, to see if I can see anything wrong, before mounting to the heat-sinks and plugging them in.
That shorted board, I will pull and inspect tonight.
While the unit is apart again, I will play with the individual card-shrouds. Then too, I guess I will order some thermal-pads. To facilitate some desired cooling, where I feel it could be improved on those operating units. The pads I was looking at, are expensive, at a consumer level. (They are all overpriced. xD) However, these had the best thermal attributes I could find, without containing metal-foils/shims...
They accept BTC, however, at this low BTC value, it is better to hold the BTC and pay with USD. (BTC has started that rise I have been talking about for the last 2 months. The last thing you want to do now, is cash-out BTC. xD)
http://www.frozencpu.com/cat/l2/g8/c487/list/p1/Thermal_Interface-Thermal_Pads_Tape.htmlI would love to use the "Ultra extreme" stuff, which is 17.0 W/mK, or the "Extreme" which is 11.0 W/mK, but not at those prices. xD
I will be getting the "Premium" stuff, with is more than acceptable at 6.0 W/mK. That is 6x to 4x better than the crap others sell as "normal". (Normal thermal pads, the kind used and sold without numbers, are usually 0.5 W/mK to 1.5 W/mK. Eg, they are just airless-foam/rubber/silicone that is heat resistant and impregnated with aluminum-oxide. xD.)
The pads are only 0.5mm thick, which is enough to raise the heat-sink off the surface of the PCB, however, I may look at getting the 1.0mm thick stuff, which I believe is similar to the stuff used on the small heat-sinks. The extra lift will break any capacitance happening between the heat-sink and the PCB itself, and even allow some air-flow under the heat-sink, adding another 30% surface-area for direct cooling. (The under side of the heat-sink, and the top exposed side of the PCB itself.)
I will be adding spacers under each screw, to "shim" the board to a matching height, enough to allow slight compression on the pads, without stressing the PCB. (This is not a solution that is as simple as it sounds. xD)
Some will be added to the tops of the inductors, as soon as I get, or make, a heat-sink for them.
AMT, a tip for applying thermal-pads, is to use a "flat roller" or just a bowed-surface...
1: Peel the backing off one side
2: Rest the pad on the curved surface
3: Using the edge of your nail, hold it in place, as you gently press the other edge to the surface to bond to... (Just the edge)
4: Roll the heat-pad down onto the surface while applying firm pressure. (That stops any large air-bubbles from forming.)
Here is the big trick to the next part...
1: Wait one day before applying this in a similar method, to the chip. (That allows the pad to "expand" back to normal.)
2: Rest one edge on the edge of a chip, and angle it downward, applying pressure towards the edge that is already in contact.
3: Use a heat-gun to heat the pad real hot... Below the SMT solder temps, obviously. (This blows-out any bubbles, by heat-evacuation/expansion.)
4: Apply slight pressure to the two taped/bonded items, and allow to cool. (That seals any "gaps", and when cooling, creates a vacuum that will pull the thermal-pad onto the surface for 100% microscopic contact.)
The alternative to that last step, is to have a vacuum chamber with a device that can apply pressure after the air has been evacuated and before the pressure has been returned to normal. That is an expensive unit. The heat trick works better anyways. Makes the bond stronger and pre-treats the unit for "operating conditions".
The issue with doing this by hand... You use your FINGER to press the pad onto the chip. The pad compresses in the center, creating a "dome". Once applied to the chip, that "dome" is now a sealed "bubble" of air and humidity. That decays the bond, stops the heat-pad from making contact where it is needed most, and ends-up in failure similar to the photo a few pages back.
I lied, there is another application method that works better, if the pads can be compressed. It involves pre-compressing them into a reverse-dome, or a bowl-like curve. However, that is best used for machines/robots to do the application, as they can hold the two surfaces flush, and lower them so the "now raised center", touches the chip first. That also stops them from having to wait 24-hours for the pad to "swell back to normal", between both applications. That swelling time is a big issue, after having been compressed.
