Hello, it's been a while since my last hack. Now I am much more lazy, so no soldering tool will be used, but if you wish to, you are welcome.
This repair is intended for all batches of S9, except batch 17+ which I didn't tested yet. Main reason was that my S9 refused to work at full speed (550Mhz) and showed a lot of "xxx" chips. Lowering frequency helped to get all chips hashing well. My boards are out of warranty, so I suggest you to not do it while you have RMA period.
This guide also helps another issue with poorly soldered inductor and whole hash board disappearing from miner status.
Here is detailed hashboard with voltage converter:
http://www.pantin.cz/20161013.jpgFirstly, look at your board and measure voltage across capacitor pins (mark A in the picture). It must be done while your miner is hashing (so at least 30s after booting). Voltage should be about 8.5-8.9V. If not, check carefully pins of inductor (mark B). If you see it is not fully soldered or you see some cracks, you will need to clean inductor wire and resolder it back.
And now, let's go to voltage adjusting hack based on LM27402 datasheet and tested my me:
measure resistor R10 resistance (mark C). Mine shows 4.86kOhm. Lowering this resistance increases voltage of whole chain, if you use pencil mod and draw on the top of R10, you will decrease its resistance. Be careful, small adjust will change voltage relatively high. Resistance of 4.5KOhm rise voltage to about 9.6V across chain.
If you want to use soldering tools, you can unsolder R10 and solder here serially connected 3.7kOhm resistor with 2.2kOhm multiturn potentiometer. This will allow you both over/underclock.
Pencil hack can be anytime reversed by cleaning R10.
My S9 which refused to work well at 550MHz, now works fine at 650MHz, but draws higher wattage. Highest voltage I tested was 10.5V, so it seems to be safe for decent OC.
This hack is at your own risk, I am not resposible for any damages you can do to your miner.