s7 300

[Paul01]

Hi all looking for some advice on a siemens s7 300. Im not familiar with the siemens plcs

i have just powered up a machine which was in storage for the last five years. The screen starts up and works but the plc when powered up does not bring on any indicator lights at all and the screen brings up a coms error. Some of the input lights are lit as expected. Am i right in saying that the plc is dead. And is the program stored on the sd card which is inthe slot in the front.

thanks

[Bryll]

Is the run switch on the CPU set to run mode ?

Do you have any memory card in the CPU ?

Is the "STOP" mode led lit (Yellow) ?

[Paul01]

Thanks bryll.

The switch is in the run mode. The sd card is in the slot and there is no leds lit 

[Bryll]

Have you really checked that you have power (24vdc) to the CPU ?

Make sure the polarity is correct !!

[Paul01]

The complete panel was just disconnected from the mains but no internal wiring was touched and there is 24v goin to the cpu and the polarity is correct. I took the cpu apart and found a solid state fuse had blown. Goin to try replace it tomorrow. The fuse is a omf 125 4A. Can this main board b got without having to replace the complete cpu if this fails. If you power up the cpu without the sd card in the slot will u get any indicator lights. 

[pop29684]

A visual check of the board for additional damage before replacing the fuse is a must. There is a reason the fuse is blue (blew) and not silver (pun intended). I would strongly advise using an ohmmeter to try to establish if there is a short circuit problem on the board. Replacing the fuse when there is a problem on the board may cause additional damage that may not be immediately discernable. I doubt that you can find a replacement board. You will likely need to replace the entire CPU. You might also consider using a third party repair service. There used to be an outfit in North Carolina that did industrial electronics repair. I don't know if they still exist or not. Seems like the name was Electrical South. (Ahhhh, I just did a quick search on the internet. It is now named Schneider Electric Repair in Greensboro, NC. I've also used a repair service out of Greer, SC. The guy was sharp. But I can't remember his name nor the name of his company. Age. SIGH.)

Once the board has been correctly repaired you should see indicator light(s) on the front of the unit when it is powered up. They may or may not change colors. There should be a catalog number on the front of the unit, on the bottom of the front cover. It may begin with the sequence 312, 313, 314, 315, 316, 317, 318, 319, or 614. Please let us know what the entire number is.

[Paul01]

The machine was in a factory and running. The panel was switched off and has been in storage for a few years until we bought it. (have the previous owner helping me with the install) When  i powered it up i found that the cpu didnt power up so curious why it blew the fuse. There is no signs of any damage on the board. i might get a electronics repair company here in ireland to have a look at it. If the cpu is powered up without the sd card will indicatorlights still light.

[Paul01]

[pop29684]

If the fuse is replaced and there are no other power issues, you should see lights of some kind on the front panel when the unit is powered up. Even if the memory card is not inserted, and even if there is no program in the user memory.