Lagunmatic 3516-SX Retrofit

I ended up connecting a different power supply hoping it would make a difference - it did not. Same behavior as before - it will output 24v and power the 7i77 just fine until I connect the common wire to the V- side of the circuit. At that point, just like the original, the PS stops supplying DC voltage.

I brought in an extension cord and disconnected the input side of the 24v power supply from everything. I supplied power to the PS with 120v from the wall. Same behavior.

Schematics for the incoming power and outputs:

Giz

Looking at the drawings you posted I can see no reason why you can't make this work. All the power supplies you add need to be completely isolated input to output, this includes any chassis ground connections. Use your ohm meter to check them out. Did you have the safety ground connected in the extension cord you used for your test? If you disconnect all the outputs on your 7I77 does the power supply still fail when connected? A sketch of how you have wired your 7I77 to everything will help. The drawings do not show the servo power supply and wiring, this will also help.

John

Thanks for the reply John. I've uploaded all the pertinent schematics here:

files.acrobat.com/a/preview/5765b1d6-b8a...a3-a9a4-8abf12ca28a0

The 24v and 5v power supplies that are feeding the 7i77 have isolated outputs, zero continuity with their input side when tested on the bench.

However I noticed tonight that when I connect PS outputs to the 7i77 I do have continuity between the input N and DC(-) on the 5v power supply. Recall input N is connected to chassis ground. I didnt have time to investigate but my first guess is that the ground connection is originating at the PC power supply and traveling to the 7i77 5v connection through the DB25 cable.

This may or may not be an issue, doesn't seem to affect the 7i77's ability to power up.

My extension cord test was done with an ungrounded cord and I did not connect chassis ground to the power supply. The PS was ungrounded. My extension cord was feeding the 24v and 5v power supplies and machines main power was shutoff.

Disconnecting all the 7i77 outputs is an interesting suggestion, I can test that tomorrow night.

Giz

I think you have found the problem. I think that the PC power supply common DC connection is connected to chassis (safety) ground, this is not that uncommon. Check for the 5V return to N connection again with the cable between the PC and the 7I77 unplugged and plugged in. If the connection goes away when unplugged then the connection to chassis ground is happening in the PC. This is one reason I like the Ethernet connection cards, no galvanic connection between the machine and the PC.

John

PC ground is chassis ground
The 7I77s 5V side (encoders and analog outputs) share this ground
The 7I77s 24V side has no connection to the 5V side so if you see this connection,
you have connected the 5V and 24V side grounds together externally (perhaps by tying the 24V common to chassis ground)

Giz, PCW

Well now we have the answer! The wiring posted clearly shows the 24V common connected to chassis ground.

John