Power Failure Recovery Problems

Hi All,

I have been asked to attend to an ancient installation which is giving problems after power failures.

The system consists of the old 3A dimmers (5104D750) and it's old Relay brothers, along with S2000 type key inputs. Later there was a B&W Touch added. The installation is not picture-book at all.

The problem is such that after power failures the key input LED's flash continuously, and the system does not respond to button presses. During those times it is also not possible to scan in the network.

At one point I disconnected one of the old power supplies, which resolved matters, but only for a while. The network voltage is approx 30V, by the way.

My suspicion is that perhaps the power supplies are giving up, but I have no way of diagnosing this properly, and do not simply want to change product. I know the whole scenario indicates network trouble as such, or a self-induced learn mode, but this does not make sense, as there were no changes to the system in the last 2 years.

Has anyone got an idea what might cause this problem? Any help will be appreciated!

 

A few things to check on an installation with early components are:

1) Is there a "Minder" on the network? If there is, disconnect and try power cycling. There was a time in the early days when the Minder would generate the "flashing LED" display you describe in certain situations.

2) Measure bus voltage at the power supply unit(s). Some early power supplies had a failure mode that sent them to 40V or higher (they should be 36V). If the voltage gets too high, communication can be affected.

3) Ensure that there is one and only one burden on the system The burden used to be provided only bt the PC Interface (early units other than PC Interfaces were not capable of providing the burden)

4) If the network has any bridge units, it should be possible to remove them and demonstrate that each network on its own can function independently. Note that a bridge may have to be replaced with a PC Interface to provide system clock

5) If you can divide the network into segments and if the trouble can be isolated to one segment only, you should be able to locate any faulty units

Good luck!

 

Hi Thomas,

What is the manufacturing date on the hardware? If it is pre '95 it could be a C7 problem.

The other thing that I would look at (as Don said) is the power supplies. Older power supplies have been known to cause unusual problems.

 

Hi Don and Peter,

Thank you both for your input.
Peter, the units which I have checked are from 2000, so we can exclude the C7 problem.

As regards you suggestions Don, it is a single network, there has been a Minder on the system, which has been disconnected long ago due to it having failed.
I will check the voltage on the sytem, but please let me know this:
I assume that the power supplies must be checked when disconneted from the network (I would assume that a single PS will not be able to raise the network voltage to 40V)?
I assume that the failure mode of the PS would be permanent, not something which would rectify itself after a power reset?

I will double check burden and so on, and will get back to you if I find something in that regard.

Thanks again
Thomas

 

The power supply need not be disconnected from the network, but the voltage must be measured at the terminals of the power supply. In my experience with old networks which have had this problem, the power supply will actually work ok as long as sufficient C-Bus loading (not resistive loading) pulls the voltage to near 36V at the terminals.

If you excessive voltage, the fault is permanent and I believe the best solution is to replace the power supply with a new unit.