Strange behavour for PCI 6516

[amamin]

Hi,

I'm using an NI PCI 6516 to control some exteral loads (solenoid valves), which require approx  16-20V to activate. I set my power supply to 20V, and have all the connections in place, and everything was running perfectly.

Yesterday, though, I noticed that one of the particular lines on Port 2 was not always switching properly (i.e., using my labview VI, which was working before, switching on that particular pin was not wokring.). I checked the voltages on it, and it turned out that it was not switching off properly. By forcing it to zero using the power supply ground, it worked fine.

The same then happened to another pin in the same port. This time, I checked all wiring, and noticed that all this time, the COM(GND) wire was not connected, but the application (except for those odd pins) was working fine. So, I connected the ground terminal to the external power supply GND, and this is when all problems happened.

First, the power supply voltage dropped. Then there was a plastic burning smell from the PC (where the relay board is). Then, of course, nothing else worked. A few hours later, I noticed that the relays were switching properly at low external power supply voltages. The external power supply did not go all the way to 20V - it stopped at about 8V. When I disconnected the COM cable, the power supply worked fine, but the relays did not switch!!! About an hour after that (all i was doing was measuring voltages at the different terminals), most of the relays started working, and the power supply was fine, with and without the GND cable connected. The only problem remaining is that all port 2 pins are not working. They switch, but only very low voltages (i.e, on is 1V, off is 0.9V).

Can anyone explain what happened...and is there hope for port 2?

thanks!

Ahmed 

[mr_]

Ahmed--

I cannot be 100% what the exact issue was.  It may be that you inadvertently wired the grounding incorrectly, which is not uncommon.  National Instruments actually started recommending that end-users install external fuses to prevent excessive current flow.  This was an attempt to reduce the possibility of damaging the board or damaging a chassis or PC, etc.  This recommendation was sent out to those who purchased this board among a few others products as you will see noted.

KnowledgeBase 4KLB51NO: Product Safety Alert: Fuses Recommended in NI 651x Applications 

If you would like to know if your board was affected by this recommendation, I have another KnowledgeBase that comments on this.

KnowledgeBase 4KLCKUNO: Which 651x Products are Affected by the April 2008 Product Safety Alert?

Do you have a wiring diagram?  It might be helpful to visualize your system.  It may be that you need to RMA your device, were you using fuses as mentioned in the KnowledgeBases that I linked above?  My best guess is that too much current was driven through the port.

Cheers!

[amamin]

Thanks for the response. I took out the board today and one of the ICs was fried (there are 4 simiar ICs, I'm assuming there is one for each port). I didn't receive this recommendation in your response 😞

I'm surprised it had worked fine without any ground wiring, and this problem occured after I wired the ground pin.