Suddently, "avrdude: Device signature = 0x000000" with ArduinoISP. Is my chip dead? I have some boards with the atmega32u4 that they were working perfectly before. I'm using an unnoficial UNO board to program them via ICSP. To power the uC I'm using two lithium batteries and a step-down converter to drop it to 5 V. 

This started happening when I tried to upload code via ISCP when the target chip was not powered by mistake.

This is my error message:

Arduino: 1.8.5 (Windows 10), Placa:"Arduino Leonardo"

avrdude: Version 6.3, compiled on Jan 17 2017 at 12:00:53
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2014 Joerg Wunsch

     Using Port                    : COM4
     Using Programmer              : stk500v1
     Overriding Baud Rate          : 19200
     AVR Part                      : ATmega32U4
     Chip Erase delay              : 9000 us
     PAGEL                         : PD7
     BS2                           : PA0
     RESET disposition             : dedicated
     RETRY pulse                   : SCK
     serial program mode           : yes
     parallel program mode         : yes
     Timeout                       : 200
     StabDelay                     : 100
     CmdexeDelay                   : 25
     SyncLoops                     : 32
     ByteDelay                     : 0
     PollIndex                     : 3
     PollValue                     : 0x53
     Memory Detail                 :

                              Block Poll               Page                       Polled
       Memory Type Mode Delay Size  Indx Paged  Size   Size #Pages MinW  MaxW   ReadBack
       ----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
       eeprom        65    20     4    0 no       1024    4      0  9000  9000 0x00 0x00
       flash         65     6   128    0 yes     32768  128    256  4500  4500 0x00 0x00
       lfuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
       hfuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
       efuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
       lock           0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
       calibration    0     0     0    0 no          1    0      0     0     0 0x00 0x00
       signature      0     0     0    0 no          3    0      0     0     0 0x00 0x00

     Programmer Type : STK500
     Description     : Atmel STK500 Version 1.x firmware
     Hardware Version: 2
     Firmware Version: 1.18
     Topcard         : Unknown
     Vtarget         : 0.0 V
     Varef           : 0.0 V
     Oscillator      : Off
     SCK period      : 0.1 us

avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.02s

avrdude: Device signature = 0x000000 (retrying)

Reading | ################################################## | 100% 0.02s

avrdude: Device signature = 0x000000 (retrying)

Reading | ################################################## | 100% 0.02s

avrdude: Device signature = 0x000000
avrdude: Yikes!  Invalid device signature.
         Double check connections and try again, or use -F to override
         this check.


avrdude done.  Thank you.


What I've already tried: 


Different programmer (another Uno board);
Uploading to a proper Leonardo board via ICSP, it worked;
Uploading to another of my boards via ICSP, it worked;
Running with the portable Arduino version;
Check if the chip is being powered with 5 V;
Changed wires and checked the connections;
The chip does not get hot;


I've been around this two days straight, any help would be much appreciated.
Mostly this error is due to connections/powering issues (as already mentioned in your output ). 


Check connections, especially power and ground also check the
resistance between Vcc and GND of your target MCU. (If it's less than
100ohm that means something is off in your circuitry or your MCU is
already fried.)
Check if your MCU is actually getting enough power (voltage and current) also check if it's getting excess voltage.
Make sure there is proper "common grounding" done between devices.
If you are sure that the above points are checked and you still get the error try the override flag -F (avrdude through shell/command-line) and if you are still not able to upload try the manually changing the address (not recommended ) in your arduino's library so that it matches with the signature it's receiving.
Finally try using a direct USB interface with atmega32u4 as atmega32u4 supports it and upload the bootloader again through an old software called Flip after that try again.


After all this if you are not able to upload then probably your MCU is dead and it might be due to an unnoticed wrong power connection or short circuit or unintentional fuse reconfiguration (highly unlikely).