A1S Output Fault

[RB211 0]

Hi all, hoping someone can shed some light on a strange problem I have encountered at several sites I visit, they are all using Mitsubishi A1S PLC's. The fault is one of an output fault on one of three output cards, say the output fault occurs on card 1 output 3, all other outputs work correctly on that and the other 2 cards, however, when the card is swapped for a new unit, so that all outputs on card one work correctly, suddenly, card two will develop an output fault immediately......... Swap this for new and another fault will occur immediately, was hoping someone has a resolve for this as it is becoming a major headache, especially as there is no reason for this to happen, logic in the PLC ladder is correct, usual safe practices are followed; ie making sure the plc is powered down when card is exchanged.

[kaare_t 155]

Are these transistor outputs? If so, I would start by checking if the power supplies to the cards are working properly. On the transistor output cards the Error led will light up if the transistors are not powered (the DC power to the card is faulty)...

[RB211 0]

No they are relay outputs from an A1sY10 Output card.

[Colin Carpenter 10]

When you say an output fault, could you say a little more about how the fault shows up. The output lights on the A1sY10 card will come on using power that the PLC picks up from the back plane, but there are separate 24VDC+ and 0V connection that need to be wired to the card to actually cause the relay contacts to change state. Without that 24 VDC, the lights will come on but nothing will happen at the output terminals. The relay contacts are rated at 2 Amps, and seem very reliable. I have occasionally know an output relay with a faulty terminals, but they're rare. I think I'd be looking hard at the field wiring of the items connected to the outputs that are playing up?