This is a modification of jstephanop's original set_voltage utility for L3+ hashboards.  This is functionally the same utility as before and as such, if you use it, you should be donating to his addresses below.

Support for the A3 (changes to the i2c protocol as well as proper version info) was borrowed from FNT's modified versions.
If you are using it for the A3, please consider donating to FNT - BTC: 1593z3zwpmCEiKf7EeXzKx799nR25NWpxD

-- From the original README
This tool allows voltage editing on Bitmain’s L3+ hashboards, it is provided free by the developer so if you find this useful and/or want me to update/provide new tools please donate to the below address. Thanks!

LTC: LQZpb8AqbggUmsdPKr28DzdNcRP7MJ8kEf
BTC: 1LeA29mLjTFCyB5J6Yiq4TFtAck2VDPUZf
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Usage:

scp binary to /config directory in your unit’s controller…this is the only directly that gets saved on reboot on antminers

Use: set_voltage <-a || -l> -c chain [-v voltage] [-qp]
You must chose -a OR -l to select A3 or L3 PIC
If you only list the chain, it will read the current voltage
If you include the optional voltage, it will set the chain's voltage
Flags: -q only outputs the voltage the pic is set to
       -p includes the pic version
Read example:
./set_voltage -a -c 1
Write example:
./set_voltage -l -c 1 -v b0

bitmains voltage controller can be configured to change the 12v input roughly +/- 1v from 10v, and this is configurable via a hex range of 0x00-0xfe, with the default being set to the middle (0x80). Higher hex values (0x80-0xfe) will LOWER voltage, lower values (0x00-0x7f) will INCREASE voltage from the default. 

For example if you want to slightly decrease your voltage on chain #1 you would input:

./set_voltage -l -c 1 -v 90

increments of 0x10 are good starting point to test a sweet spot for each board for a particular frequency. Lowering voltage until you get around 1 HW error per minute is usually a good reference “sweet spot”