[Antminer S1] - Pencil Voltage Mod guide

[GenTarkin]

BTW, just an update after a few days, the antminer is still goin strong, avging 213GH @ 418mhz @ .31 %HW ... the avg voltage has climbed to 1.17v on all chips - think theres a settling period or something..

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[tacotime]

I wouldn't super be into pencil modding these, a bunch of the components involved in voltage regulation are already overloaded about four fold at stock voltage.

[GenTarkin]

I wouldn't super be into pencil modding these, a bunch of the components involved in voltage regulation are already overloaded about four fold at stock voltage.

Four fold? I highly doubt that, otherwise shit would be on fire. They are over spec a bit ... but seem to tolerate it fine and components absolute maximum power output, like the main IC for the VRM ..., is nowhere near its maximum.

But as far as capacitors and shit, I have no idea =P

[tacotime]

gmaxwell was the one who mentioned it to me, if you can track him down you might be able to figure out which components you might need to replace.

[jimrome]

... the avg voltage has climbed to 1.17v on all chips - think theres a settling period or something..

You're very likely seeing the resistance of the pencil carbon change as it warms and cools. Once you've established the ideal nominal resistance you might want to replace the resistor/pencil for temperature stable resistors. Could also just be carbon flaking off?

As far as overloading the parts is concerned, that little buck regulator is only rated to ~30A, but is capable of supplying much more (core is rated to 40A IIRC). It has built-in thermal protection so the chances of frying it are low - instead of smoke you would instead have thermal shutdowns until the temp returns to 'safe' level.

These shutdowns can be mitigated or even avoided if heat sinks are applied to the back side of the regulator, (which is on the back side of the PCBs obviously). We did this pretty extensively when modding bitfury boards, which use the same part: https://bitcointalk.org/index.php?topic=251966.msg3152210#msg3152210

[GenTarkin]

... the avg voltage has climbed to 1.17v on all chips - think theres a settling period or something..

You're very likely seeing the resistance of the pencil carbon change as it warms and cools. Once you've established the ideal nominal resistance you might want to replace the resistor/pencil for temperature stable resistors. Could also just be carbon flaking off?

As far as overloading the parts is concerned, that little buck regulator is only rated to ~30A, but is capable of supplying much more (core is rated to 40A IIRC). It has built-in thermal protection so the chances of frying it are low - instead of smoke you would instead have thermal shutdowns until the temp returns to 'safe' level.

These shutdowns can be mitigated or even avoided if heat sinks are applied to the back side of the regulator, (which is on the back side of the PCBs obviously). We did this pretty extensively when modding bitfury boards, which use the same part: https://bitcointalk.org/index.php?topic=251966.msg3152210#msg3152210

Thanks for the informative post! ... been looking for an answer like this regarding that IC
I figured its current handling capabilities were more closely dependent on the temperature it reached.

[GenTarkin]

Also, Im wondering, what exactly draws the current on that particular buck regulator. Just the ASIC chips VDD? because, if so, at 1.1v the (x8) ASICs draw far less than 30A on their VDD, and based on the increase of Amps shown in the datasheet, figuring 1.2v would put the (x8) chips @ 3.9A or so, would only draw just above 30A

[jacob019]

Nice work GenTarkin!

Really interested in undervolting to the extend the useful life of our S1's down the road. 

1.  Would increasing the resistance at R12 have the desired effect?
2.  How far can we go?
3.  How did you calculate the resistance target?

[GenTarkin]

Nice work GenTarkin!

Really interested in undervolting to the extend the useful life of our S1's down the road. 

1.  Would increasing the resistance at R12 have the desired effect?
2.  How far can we go?
3.  How did you calculate the resistance target?

Ive not tried undervolting but theres a thread where someone is going to do that w/ the R12 resistor =) They are gonna attempt .75v @ 200mhz or so ... iirc'

I didnt calculate resistance really, I just dropped the resistance about 1k at first on the R3 using a pencil and then booting the antminer up and measurig ASIC voltage.
Based on that result, I further experimented w/ more & less resistance accordingly.