6602 Board Pin 1 is Not 5 Volts

[otheredward]

Dear All,

In tracking down an unrelated problem I found that my pin 1 (listed as +5V for the 6602 board) is at 1.64 volts with respect to any of the D GND pins. When I check the voltage between pin 1 and any of the G GND pins its about -100mV. I'm using a SH68-68-D1 cable connected to a TBX-68 breakout board. I'm checking pin 1's voltage with a digital multimeter. Any ideas why pin 1 wouldn't give me +5V with respect to the D GNDs?

Also, perhaps I should know this but why does this board have and what is the difference between the D and G GND pins?

Thanks,

Ed

[Scott_A]

Hi Edward,

First things first, make sure you are only referencing the 5V pin to D GND.

Looking at the pinout, I'm not seeing the other grounds you are talking about, but there may be a global ground or reference ground in addition to digital ground.  I'll attach a picture of the pinout of a 6602 with the SH68-68-D1 cable.

Has the 5V out ever worked?  When hooked up through a multimeter to the digital ground it always reads around 1.64 V?

[otheredward]

Hi Scott,

Thanks for the board pinout. The 6602 board shipped with a sticker that has the board pinout, this is different depending on the cable used? The sticker shows some pins as "R GND" not "reserved" which I've always wondered about. In any case, when referenced to digital ground pin 1 always gives +1.64 volts. If I set any of the PFI lines to high using the Measurement & Automation application my multimeter shows they're at 5 volts with respect to digital ground. I'm not sure if the +5 volt out has ever worked. We got the board a few years ago and haven't used it much until now. I don't recall if it was ever checked. I've only checked recently as I'm starting to use the board more and am having trouble getting any of the PFI lines to trigger another device. The device I'm trying to trigger says the thing triggering it must be able to sink 100mA and I wonder if this is the problem. So I don't know if the +5 volt out pin ever worked but it doesn't appear to work now. Is this suggestive of a greater problem I should be worried about?

Thanks,

Ed

[otheredward]

Dear all,

Specifically, I have a light sensitive detector, Perkin Elmer SPCM-AQR (a fiber coupled APD). It has two BNC connectors, output and gate. When a photon hits the detector a TTL pulse is output on the output BNC. The gate BNC connection allows the device to be shut off when the gate connection is set to zero volts and turned on when at 5 volts (TTL high low). There is a pull up resistor connecting the gate to the device's 5 volt power supply so if nothing is connected to the gate input the device is on. The SPCM is 50 ohm on both connections. If you call Perkin Elmer they'll send you a rough diagram of how to connect the gate BNC to a function generator. I've attached it to this post as a PDF. Perkin Elmer notes that in order to use the gate function on their SPCM the device connected to the gate BNC, in my case the 6602 board, must be able to sink greater than 100mA. I found a post here that says the 6602 board can't sink more than 24mA when outputting logic low. There is also some mention of damage to the board when trying to sink too much current and I wonder if this could be related to the +5 volt output of pin 1 not being at 5 volts.

Am I correct in understanding that I will not beable to gate my SPCM directly with the 6602 board becuase it can't sink enough current?

Please excuse the length of this post. These are two common decives in the microscopy world and I figure other people must have had this problem too. So I thought I'd put it out there.

Thanks,

Ed

[Scott_A]

Hi Ed,

There are minor differences in your device pinout depending on the cable you use (and you can see these differences in MAX under NI-DAQmx Device Terminals Help).  The difference is that some of the grounds that are available with non shielded cables are reserved with the shielded cables.

The fact that you reliably get around 1.6V on that line makes me think that this may need to be RMA'd but before you do that I would contact our support team directly via phone (1-866-ASK-MYNI)

I will check for you regarding the 6602 being able to sink enough current, but 100mA seems rather high for a sink.

[otheredward]

Hi Scott,

Thanks for the info regarding the use of diffrent cables. I will get in touch with the support team and see what happens. I did find this posting

http://forums.ni.com/t5/Counter-Timer/PCI6602-output-sink-mode/td-p/787431

in which a NI engineer says you can only sink 24mA on logic low.

Any recommendations on how to make a buffer to sink more current?

Thanks again,

Ed

[Scott_A]

Hi Ed,

The max sink and source current is set when the card is made and there aren't properties that will allow you to change it.  You may be raise the sinking current by building an external circuit.  I would be wary of trying to change that setting however as it may damage the card in the process.

[cholulteca]

Hi Scott, has there been any solution to this issue? I'm facing almost the same problem, the -5V pin gives me 2.2V (measured with both multimeter and oscilloscope with 1M input impedance). Also, this output depends on whether I set any other digital line - if no digital output is set to high, I don't get any voltage at all. I want to build an external circuitry with just some logic gates and use the board's supply voltage to be sure to not get any floating grounds, but of course 2.2V wouldn't do. Any help is greatly appreciated!

[Scott_A]

Hi there,

If possible could you call in to 1(866) ASK-MYNI and we can further troubleshoot it the card.  It may be something simple that we are overlooking or perhaps the card needs to be replaced.

[cholulteca]

Hi Scott, I just got the card back from our electrical engineer, and he said most probably there is just no supply voltage. The 2.2V are generated from backward signals when the digital outputs are switched. I now power the card with an external 5V supply and everything looks fine, I have no strange effects whatsoever any more. Perhaps it is an issue of the mainboard which just doesn't supply the 5V? Thanks anyway! Svenja