The ground pin floating to +16V would indicate that there was no return path for the phantom power (input and output audio ground being on the same pin 5 of the API connector). The pre has a phantom power option. A typical rack like an API rack grounds the ground pin in some way for that phantom return. It could be that the designers expected that ground to exist to power the relays or control the relays that they put on board (which did not exist in the same arrangement in the 1081).
I don't have a schematic for the unit, and I haven't looked at the 1081 schematic in a while and so have no position about the pin 1 grounding on that preamp. I am simply looking at the data from a diagnostic narrowing perspective.
The OP is not clear and at the start I thought he had some module that had a power switch on it. Upon reading the OP I thought that he was turning the unit on with the buttons, which seemed odd, but now I understand that his problem occurs when he activates any of the powered relays controlled by the front panel switches (+48, imp, phas and +30db I think).
Then I saw that he tried it in three racks, 1 worked, two didn't. The one that worked has it's own PSU, he did not specify the PSU for second, and he is using his own PSU for the third.
I am assuming that if it was a power up problem then the problem would occur before he pushed the buttons maybe? Could be wrong there.
If there is +16V on the output ground pin we can be pretty sure that with some connections ( i would hazard a guess MOST connections) that pin would be grounded by connecting it to any input. If he plugged this modules output into any reasonable input it would ground that pin and so I suspect that condition is not a design feature but a wiring problem. The fact that installed in the API rack the output does not show this +16V ground seems to confirm that.
So I suspect the grounding arrangement of his rack is interfering with the operation of the switches lights and relays on the front of the module.
I don't have a schematic for the unit, and I haven't looked at the 1081 schematic in a while and so have no position about the pin 1 grounding on that preamp. I am simply looking at the data from a diagnostic narrowing perspective.
The OP is not clear and at the start I thought he had some module that had a power switch on it. Upon reading the OP I thought that he was turning the unit on with the buttons, which seemed odd, but now I understand that his problem occurs when he activates any of the powered relays controlled by the front panel switches (+48, imp, phas and +30db I think).
Then I saw that he tried it in three racks, 1 worked, two didn't. The one that worked has it's own PSU, he did not specify the PSU for second, and he is using his own PSU for the third.
I am assuming that if it was a power up problem then the problem would occur before he pushed the buttons maybe? Could be wrong there.
If there is +16V on the output ground pin we can be pretty sure that with some connections ( i would hazard a guess MOST connections) that pin would be grounded by connecting it to any input. If he plugged this modules output into any reasonable input it would ground that pin and so I suspect that condition is not a design feature but a wiring problem. The fact that installed in the API rack the output does not show this +16V ground seems to confirm that.
So I suspect the grounding arrangement of his rack is interfering with the operation of the switches lights and relays on the front of the module.
