Quote from: Lumanet on September 27, 2014, 06:44:32 PM

Hi Guys,

I am working on this underclocking as well and I got some different results when you use USA Power 120V. First I also tried the pencel mod but wasn't 100% happy with it so I did some researching on my own and found out if you really replace those resistors :

R3, R66, R38, R52

The original capacity of the resistor is: 8.2 - 8.3 K Ohm

I replaced them with an 0603 resistor with 4.12 K Ohm

This got my Antminer's so far down that 3 of those now only do use ~612 Watt. This allowed me now to reduce the GHs/Watt costs to be :

Original 1650 Watt for ~ 600 GHS = 2.75 Watt/GHS

With the new Setup I get :

Tuned 620 Watt for ~ 400 GHS = 1.55 Watt/GHS

So if you do your math now you do recude your Power consumption by over 43% without buying new Hardware. All you do need to buy is a few 0603 4.12K Ohm resistors which cost like 3$ for 100 on eBay maybe even less.

If you decide to do this with a normal solder iron use a thin pair of tweezers so you can hold the resistor better when you remove the old one. I did start with the left side first which is closer to the next resistor on the left. Since they are SMD you can apply some heat to is and it also soften the other end of the resistor so much that you can lift one end of the Circuit Board. Then you do the other side and you have your resistor removed.
Next apply some solder to the left spot on the Circuit board and with help of your tweezers solder the new one in place as flat and good as possible. Than do the other end and measure with the Ohm Voltmeter and you should get between 2.8 - 2.9 K Ohm. Ensure you soldered it in place so it don't come loose.

!!! WARNING !!!!

When I did one of the 6 boards I did mistakenly not solder one resistor perfectly flat onto the ciruit board and when I put Power onto it it burned me 4 of the 8 Chips. When I did remeasure I noticed I suddenly had the wrong OHM which caused an over voltage to the chip. So please measure twice.

Once done SSH into your Antminer to ensure it benefits from it's now lower Voltage by adjusting the multiplexing for chips :

   option 'freq_value' '0A81' #275M
   option 'chip_freq' '275'
   option 'timeout' '45'

This is the best Value you can archive now. Going higher or lower will reduce your GHS power.

Some other help for this modding (Freg|Timeout|HEX) :

250.00 56 0981, 1385, 4981, 5382, 5385, 6786
256.25 54 1405, 5405
262.50 53 0a01, 1485, 4a01, 5485
268.75 52 1505, 5505
275.00 50 0a81, 1585, 4a81, 5585
281.25 49 1605, 5605
287.50 48 0b01, 1685, 4b01, 5685
293.75 47 1705, 5705
300.00 46 0580, 0b81, 0b84, 1785, 4b81, 5785
306.25 45 5805
312.50 44 0c04, 4c01, 5885
318.75 43 5905
325.00 43 0600, 0c84, 4c81, 5985
331.25 42 5a05
337.50 41 0d04, 4d01, 5a85
343.75 40 5b05
350.00 40 0680, 0d84, 4d81, 5b85

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Also a big thing I noticed is if you lift the little Controller board and tape the top between the 2 Boards with Tape you get a much much better Airflow as you can see on the photo below :

http://i.imgur.com/l3QtRlr.jpg

http://i.imgur.com/bjVin15.jpg

This board is modded with new 4.12 K Ohm resistors.

http://i.imgur.com/Tuo8ZGt.jpg

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Lumanet Solar Energy LLC ( http://www.lumanetsolarenergy.com )

We do also offer soon remoded hashboards for sale over our Portal. Also we work on a 800Watt Server Power Supply Combo which will be below $80 but has a 69Amp 12V Rail. Which can be used to feed up to 4 underclocked Antminer S1 or 2 Antminer S3

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attach sreen of asic's temp and speedfans rpm,please.