Allen Bradley PLC5 Outputs Problem

[daba]

To use 1/2-slot addressing the rack backplane switches must be set...

Sw-1 could be on or off, controls output state on hardware failure
Sw-2 OFF
Sw-3 OFF
Sw-4 ON
Sw-5 OFF
Sw-6 could be on or off, controls EEPROM transfer
Sw-7 could be on or off, controls EEPROM transfer
Sw-8 could be on or off, but most likely OFF

Try re-seating the switches by turning them all opposite and back again.

Remember DO NOT pull the PLC out of the rack with the power on !!!

 

[Ken Roach]

Let's take a bit of a step back and eliminate some of the possible issues.

The 1771-OBN modules, as you have described, are 32-point DC output modules which are twice as dense as a conventional PLC-5 output module. While the points are numbered 0 through 17, the PLC-5 uses the old PLC-2 octal addressing method for I/O, so there's no "8" or "9" and there are just 16 bits per data word.

It's nearly impossible for the firmware or program to be at fault.

But there could be a power problem or an addressing problem arising from the backplane interface.

Let's make sure we are referring to the modules correctly both in their physical location and in I/O memory.

In "1/2 Slot addressing" mode, every physical slot is allocated two Words of Input data and two words of Output data. This allows you to use 32-point modules.

By convention, let's refer to the first I/O module as Module 0. You can have 4, 8, 12, or 16-slot chassis.

My colleague Paul referred to the addresses but I want to be very thorough:

CPU Slot
Physical Slot 0 I:000, I:001, O:000, O:001
Physical Slot 1 I:002, I:003, O:002, O:003
Physical Slot 2 I:004, I:005, O:004, O:005
Physical Slot 3 I:006, I:007, O:006, O:007
Physical Slot 4 I:010, I:011, O:010, O:011
Physical Slot 5 I:012, I:013, O:012, O:013
Physical Slot 6 I:014, I:015, O:014, O:015
Physical Slot 7 I:016, I:017, O:016, O:017
Physical Slot 8 I:020, I:021, O:020, O:021
Physical Slot 9 I:022, I:023, O:022, O:023
Physical Slot 10 I:024, I:025, O:024, O:025
Physical Slot 11 I:026, I:027, O:026, O:027
Physical Slot 12 I:030, I:031, O:030, O:031
Physical Slot 13 I:032, I:033, O:032, O:033
Physical Slot 14 I:034, I:035, O:034, O:035
Physical Slot 15 I:036, I:037, O:036, O:037

 

[Ken Roach]

When you look at the Installation Instructions for that module, you'll see there is a single onboard Fuse (and Fuse Indicator) but that the output power is divided into 4 DC+/ DC Common groups. Check to be sure that all four DC+ and DC Common are connected and at the appropriate voltages.

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1771-in034_-en-p.pdf

I would troubleshoot this by finding an output that is relative unimportant: either un-used or connected to something that won't produce motion (like a pilot light). Poke or force zeroes and ones into the Output data address for that point and verify that the point you think should be activating really is. Do this both for the "left side" and the "right side" addresses.

As an alternative, look at the Data Table for each "left side" that is showing data and make sure it matches the bit pattern that's physically on the module.

If the Chassis density selection is actually incorrect or mis-interpreted, then I think that the "left hand side" will not indicate the correct data either.

 

[YWengineer]

Thankyou Gents.

This is an amazing Forum.

We appear to have got our outputs back.

Powered down and removed all cards including processor to inspect back plane.

Re-fitted Output cards and processor, left Analogue cards out and re-powered up.

Outputs were restored !

Powered down again and re-fitted Analogue cards. Still working.

No software or hardware changes.

Now Testing Plant !

Your help is much appreciated here in Yorkshire.

 

[Mickey]

Good to hear and thanks for coming back with the solution.

And welcome to the forum.