Meantime just fixed a pair of S7's that came in the door. Both had pretty burned plugs:



And after repairs we have nice new nickel plugs...



The trick to doing a proper plug replacement is as follows:
1) preheat: You have to get the board hot enough to allow the solder to be molten for a bit, both to get the old plug off and to remove the old solder.
2) rosin solder: Has a slightly lower melting point than ROHS crap: Use it to alloy the solder on the pins, reduces the temp a lot
3) Air heat: Use to heat all the pins at once allowing you to easily remove the plugs.

Then clean up the pads, flux the new plug, put in, warm up, and solder. A good preheater can make the difference. Trying to do it without one will result in damaged pads and Vias, which will not be able to conduct the proper amount of current.

Ok, eggnog all drunk. I just also fixed a pair of S7's and a bunch of Neptune controller boards so once I get these titans completed I can take a look. In the meantime I have another thread about my findings on S7/S9 boards, some of them have real quality control problems (if the heat sinks are not all lined up you will have serious airflow issues for starter. Factory problem). The thread is at:

https://bitcointalk.org/index.php?topic=2650906

C

Morning everyone! Made some good progress with S7 problems this week, let's check in and see how ole bitcoin is doing!!!

12.7. Hm....

So is this people selling to catch year end tax bennies, or the end of the world? If the former then no big one. If the latter that's a problem. I'm HODLing through 2018, will be interesting to see what it does Jan 1.

Check in hardware settings/device manager to see if a COM port is appearing. Also if the thing has two plugs you need to use the special 4.20 version of BFGMiner. If three use the latest version.

C

However that doesn't mean I give up: I just bought a reflow oven before the end of the year, will use that to try and re-seat all of the hashing chips before throwing in the beer when it arrives.

Just an excuse to buy bigger tools.

Morons. :-) Meantime looks like we will be stuck here at the 14-15k range for awhile and for fuck's sake use a pool of sharks at the bottom of your trap door pit. With a nice viewing room with classical art and music piped in so you can watch.

Indeed. Those dry cleaning people are fond of putting microdot cameras on your clothes, powered by static electricity.

But where people really blow it is failing to do an enema before entering the room with the computer. Because you know what kind of people proctologists are, and they have been known to sneak into people's bedrooms at night to plant their malware....

Colon blow: It's not just for breakfast anymore...

C

Just been busy with Titan controllers (everyone's running Neptunes all of a sudden), Christmas, and Eggnog. Lots of eggnog....

Nothing works and I had to put it aside for a bit to fix some titan boards. And enjoy Christmas. And eggnog. And stuff like that.....

True true, that does work, but it would be nice to have your own little mini-trezor server so you could still use the damn thing. I absolutely hate relying on a vendor and their web site.

Yeah, Trezor. My only question there is what happens if they get hacked, and is there a way to run your own trezor server on your own system (so you don't every have to depend on the Trezor company to be in business)?

Indeed. And while I am a true tool snob in some respects (I love snap-on tools; they never will gall a bolt or fail to grip a head and the micro-movement of their ratchets is God) I have to say the Aoyue stuff ain't bad. Their SMD soldering tweezers are a complete joke, but their irons aren't bad (but very under powered for de soldering wick) and that dopey air tool works well.

I'm counting my bitpennies now and thinking about buying a Hakko FM202 and 20203 SMD mini-tweezer set so I don't have to keep blasting 0402 sized components with air to stick them (trying to do it with an iron sucks; the things just stand up on the board and it's like aarrggh). Hakko makes good gear, but I haven't tried their air tools.

The $25k rework stations are designed to be set up to do a specific process, then turned loose with entry level people at the controls. Not something I'd be up for.

And don't forget a good pre-heater, the Aoyue 853 and 853/a are pretty good but I have had to resolder wires inside it twice. Then again I bang it around a lot on the road, so there's that.

Now on to Bitcoin: I see we're hanging around 14k. That's not bad, but not moon-worthy. Someone poke the damn badger already....

Strangely enough my Aoyue 952 has done very well. Solid little thing.

I think I'm going to get a ez-bake oven to try to do better chip reflows. I can do it by hand, but there is always the risk I overheat the chip. Reflow oven would automate that, then I just need to make sure the tacky flux has the component perfectly aligned (you can bump a chip slightly with air to get it to perfectly center.

Quite possibly, this board was assembled by what I like to call a shirker. I've seen other pictures on Ebay and wondered if the sinks were loose/off, but it seems they're glued on.

It does take some time to re-mount sinks properly, you need to put a thin layer of adhesive compound on the chip, equal amount on the sink, press together and hold/align, etc. They just went whomp.

As for putting sinks on the FETs, it's best to put them on the board behind the FETs. TO style chips have a nice big drain pad and are designed to pull heat *down* and not up through the gate. Putting sinks on top of the FETs pulls hte heat through the chip, you want it to go away into the board.

C

Meantime I am doing something stupid. In addition to pre-paying my property taxes I am pulling the money to do this from reserve lines of credit instead of tapping some bitcoin profits. Once the new year ticks over I get a lot better tax breaks on work/bitcoins, and I'll just sell some pennies and pay off the loan in Jan.

I really don't like doing this though. But coupling end of year purchases, new reflow oven (always wanted an ez-bake oven!), and other stuff I am low on cash. Bad me. Bad bad me.

Ug.

That's an interesting question: Normally when you have a boost/buck power supply you want to size your fets for both current capacity and dwell time. Dwell time is the time the FET has to spend "on" and the amount of time it takes to turn it "off" then "on" again.

So for example if you have to step 12v down to 1v for a single chip miner you need FETs that are on 11/12th of the time to ground, and 1/12th of the time to +12. This means that the high side FETs have to switch 12 times faster than the low side ones. The transition time is when the heat occurs, because you're switching and you want that period to be as short as possible. Likewise when you turn off you have to have the gate interrupt the power flow, and that takes time/generates heat. So you want a really fast switching FET with a narrow trench and low capacitance.

Problem is the best high current FETs have nice large gate junctions so they're slow. You can switch at a slower rate, but that causes a lot more ripple which has to be smoothed by the chokes and the capacitors. And THAT generates heat.

This is why on the S7's they used two FETs on the high side (12v) and one FET to switch the low side. Since they were only bucking from 12v to 10.5 or so most of the time the FETs are "on" with a small amount of "off". For the S9's they seem to start at 9.5v or so, and thus added a second FET on the low side. Which might be causing problems including more heat (thus they stuck a heat sink on the back side of the FETs, surprise!) as well as more shorted FETs which short out the power supply.

They should have switched to a different single FET which would have lower capacitance (capacitors in parallel add value like resistors in series) but for some reason they didn't.

By the way, this seriously nailed BFL on the Monarchs. They finally went with high power high frequency FETs on the high side but you can see where they had the pads to run TO style FETs. They also had 6 phase power supplies to smooth out the current, but that meant each FET was switching 6 times as quickly. Real bitch on wheels, if they had put their engines in series instead of parallel it would have been more like the Ants and easier to design.

Another side note: This is why you don't ever run an antminer at higher than 12v. Higher input voltage would just require more bucking which means more heat and the usual failures.....

I think a similar problem exists in the S9's. Might explain some of the reliability problems. Fortunately replacing FETs is not hard if you have air heat and significant preheating ability to remove the FETs and reflow new ones.

It's always tricky to find hashing chips, and normally it is not the chips themselves but the supporting technology that goes foom. Usually it's either the clock crystal (S7), the power scale chip (s7) or the FETs (S7, S9) that die, Those are easy to replace.

When hashing chips go bad it normally sucks: There's possibly damage under the chip and although these are not as bad a QFN chips they are still a pain and finding a blown chip under these heat sinks is not a joy. On Avalon units the solder typically extrudes under the chip, shorting out the communication lines. On a unit with individual heat sinks like Ants, it's normally the chip that burns up.

This is also a S9, not an S7. There are plenty of S7 chips, just grab a torched board and pull chips off it then re-tin and swap.

C

Ok, let's get started. Our latest board of the hour came in with the usual it doesn't work problem. There are a couple of types of it doesn't work:

It blows up the power supply and shorts out.
It comes up but does not hash
It doesn't come up.

First thing to check is to see if anything is unusual about the board. In this case, not really other than the fact that the heat sinks look like they were put on by a 5 year old. I spend a lot of time aligning heat sinks on S7's to be perfectly straight to minimize airflow turbulence since these things are air cooled in small boxes.

However I did notice that one was a little bit loose, could wiggle it a bit like a loose tooth. That's bad. Using the nose I could smell a bit of burned smell at that point on the board, greeeeeat......

So put the board on the preheater, warmed up the board, then used the air tools to warm up the heat sink. Not too difficult, and it came right off leaving this:



Now for a close up of the chip...


And a side view of the chip.


And a view of the heat sink itself.


Using these we can see the problem: This chips is one of the ones that does not have a heat sink on the bottom, and more importantly has only about 50% of the chip covered with the heat sink glue.

From what I can see here it looks like a sloppy Bitmain job when building it led to a board that would run somewhat warm anyway. The chip itself only had 50% contact with the sink, and judging how thick that compound is it looks like the compound made a poor connection between the chip and sink. Over time the chip got warm, had a lower resistance because it is in a series string, pulled more current, more heat, and the usual failure.

Bitmain should warranty this board, but it's probably out of warranty. The lack of compound on the whole chip points to a manufacturing fail.

Solution: We could pull the chip, but that gets complex and I need to talk to the owner before doing that. Likewise if the SCL signal goes through every chip in the board in series, removing the chip breaks the chain and the board does not work. Drat. Wonder if bitmain will sell me a bunch of chips....

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