Error,

I do not recal seeing a base thread now that you mention it. So check the value of servo thread, it should be 1000000.
If you are getting real time errors with the correct servo thread, the PC is acting up or there is something causing delays.

I received a new PPMC encoder card from John. Linux CNC will boot.

The drives and contacts are all pulsing on and off. It is fast enough that the axes will even get through homing but I am afraid that it will damage the machine.

Have you checked the power source for the relays?

If you have a faulty power source the voltage drop maybe enough to cause your relays to cycle as you described. Using a voltmeter could quickly rule it out.

Check for shorts ect from the source of power to the next relay then work your way downstream of the power flow.

Also check for AC voltage on the DC side, that would indicate a shorted diode. Check also the power drop on the DC side when that occurs, capacitors might be dry.

All the voltages that should be present appear to be present. I am not finding AC on the DC side. That is checking from my supply sources and at the relays. They are just turning on and off.

Try to identify if you have a ground that switches to power/enable your relay.

Meaning - instead of a power source going to your relay to power it, another relay controls the ground [-neg/0V] to activate the relay. Power already present at that specific relay waiting on a [-neg/0V] source to activate.

In my set-up on the the interact I had a relay that switched [fluttered] like you stated and it was controlled by a [-neg/0V] switching relay, I found a bad [-neg/0V] wire. It rang out fine, but could not handle any significant load.

Is this all your relays doing this? Or is it a section that controls a specific area?

Can you try to disable/disconnect relays in the series [assuming the problematic ones are in a series] to identify if one is failing causing a cascading effect. I know electrical gremlins are difficult to track down.

If you want give me a call and I can try to give you hand in troubleshooting.