“Boards OK” shows whether the release chain of the channel boards is closed. The boards are connected in series via the internal bus, and each one closes its part of the chain only as long as it sees no reason to shut down itself. Only when the whole chain is closed can the main contactor be commanded at all – an interlock in the hardware that no software can bypass. The ladder diagram in Figure 26 shows how it fits together.

If the tick is missing, look at the “Enable” fields next to it:

A tick is missing there too

Exactly this board is holding the chain open. Its error log names the reason, see FAQ-06, “Contactor does not pick up”.

All enables are set

Every board releases, and still the chain is interrupted. Usually a channel board is then not fully seated in its slot: it is supplied and reports on the bus, but the contacts of the release chain do not close yet. Less often the cause is a bus connector, a cable between the boards or a board without supply.

Which board interrupts the chain is not shown by the device: the “Enable” field only reports what the board itself switches, and “Boards OK” is a single signal for the whole chain. Therefore reseat all controller modules – a controller module is the heat sink with its channel board:

1. Switch the device off, pull the mains plug, check for absence of voltage and open the housing as described in Chapter 15, “Maintenance and repair”.
2. For each controller module: loosen the four screws (TX20), pull the module out of its slot and push it back in as far as it will go.
3. Tighten the four screws again. They hold the module in its slot.
4. Close the device and switch it on. Once it has started up, “Boards OK” must be set.

If “Boards OK” is still missing afterwards, notify customer service.

“Boards OK” has nothing to do with the external release or emergency-stop circuit: if that is open, the feedback is missing, see FAQ-06, “Contactor does not pick up”.