Trouble shooting IO modules on PLC - strange respond! Need guide

[ckchew666]

Hi,

Our customer have an old Mitsubishi A1 series PLC which is not running for some time. We are doing the commissiong and point test on the system. It has DC Input & Output modules.

When we stimulate the limit switches, we see Input LED at the 32 points DI module turn on, we measure that particular point with multimeter and it shows 24VDC, but the spooky thing is we do not see any signal/Input in the ladder program when we go online with it! Sames goes to output as well.

Is there anything wrong with the CPU or the backplane? As from what I guess, the IO points are directly to/from the IO modules, if something goes wrong with the CPU & backplane, the ladder program will not be able to read the information/status of the IO modules, am i right?

Or what could be another possiblity? Hope someone can guide.....Thx.

 

[Thomas Sullens]

online

ckchew666 look on your tool bar when online. On some plcs you have to tell it you want to see whats happening even though your online. I know AD is like this im not sure about Mitsubishi A1.

 

[ckchew666]

ckchew666 look on your tool bar when online. On some plcs you have to tell it you want to see whats happening even though your online. I know AD is like this im not sure about Mitsubishi A1.

Thx, will check with the programmer. The same programer has actually commission another line in the same plant using A2 Mitsubishi no problem at all. We are thinking to exchange the modules with A2

 

[BobB]

Is the PLC in run mode?

 

[E O'Sull]

A1s

When you say you can go on-line, which software are you using
MEDOC or GX Developer?

On the CPU is the Keyswitch set to Run, and are the Power & Run LED's illuminated?

Can you verify the program from your PC to the PLC?

You can monitor the value in D9008 which if an error occurs during self-checking can give you a guide / description of the error and possible recovery method.

Is the first card the 32 Input module, and hence normally allocated as
X0 - XF / X10 - X1F. Is this the input range allocated on your program?

Regards, Gene

 

[Unregistered]

Hi,

Thx for everyone's feedback, yeah the cpu is in RUN Mode.

We've found out the reason, it's the faulty Input card that cause the problem. Luckily it's the first Input module, we change the Input module with another running machine and everything's okie.

Thx