Just purchased on eBay an S7 300 312 CPU.  On power up, all LED lights blink once, briefly, then out.

Memory card is in the unit.  No idea what is on it.

Holding the switch to the MRES position does nothing (no lights).

Did I buy another DOA?

Any help appreciated.

Hello,

you said that all lights go out, but led Power and Stop doesn't lights permanently??? You must make tests as we've talking about in old thread, without MCard too. When you put MCard out, red light must apear on SF probably, then 3x procedure with MRES key must do the job. Give info.

hi Pilot,

try to so a Reset to factory settings, described in this manual in chapter 9.5:

SIMATIC S7-300 CPU 31xC and CPU 31x: Installation

Procedure from manual

Proceed as follows in order to reset a CPU to the delivery state via the mode selector switch:

1. Switch off the supply voltage.

2. Remove the SIMATIC Micro Memory Card from the CPU.

3. Hold the mode selector switch in the MRES setting and switch the supply voltage on again.

4. Wait until LED lamp image 1 from the subsequent overview is displayed.

5. Release the mode selector switch, set it back to MRES within 3 seconds and hold it in this position.

6. Wait until LED lamp image 2 from the next overview is displayed. This lamp image lights up for approximately five seconds, that is for the duration of RESET. During this period you can abort the resetting procedure by releasing the mode selector switch.

7. Wait until LED lamp image 3 from the subsequent overview is displayed and release the mode selector switch again. The CPU is now reset to the delivery state. It starts without buffering (all LEDs are lit) and changes to the STOP mode.

Then try to connect to the CPU with the settings described in the manual.

hope this helps, 

regards,

Hello,

pls Admin close this thread, solved at another place, thnx.

Closed cause question posted twice.

The second thread with the subject S7-300 CPU all lights on - BUSF red (not flashing) is published within the conference SIMATIC S7-300 / S7-300F.

Best regards
Min_Moderator