Qnet2 DAQ card tips'n'tricks

This is a list of common problems with the DAQ card electronics and how to fix them. We will add more items as they come...

One input channel doesn't work? Probably shorted protection diode.

We already had two incidents where a badly arcing PMT base damaged one of the protection diodes in such a way that it became a short circuit. In both cases the input became shorted with the -5V supply reference on the board. As a result the input didn't work anymore. In addition, the overall threshold settings of the other 3 channels got affected by the -5V supply dropping below -4.0V (since the 50 Ohm terminator of the damaged input and the PMT base in parallel were now directly connected to -5V via the shorted diode and thereby overloading the -5V...).

What to do?

Check with an Ohmmeter the diode on the suspicious input:

• channel 1: "D1" (next to BNC receptacle "P1").
• channel 2: "D2" (next to BNC receptacle "P2").
• channel 3: "D6" (next to BNC receptacle "P3").
• channel 4: "D7" (next to BNC receptacle "P5").

If you find a short (i.e. less than 5 Ohms) between the center pin and one of the two outer pins of the diode, then it needs to be replaced with a new one. Please contact Hans to get a spare from the UW lab or have it de/soldered.

Used a 12V DC supply on the DAQ card instead 5V? Another protection diode damaged...

Unfortunately, the power connector of the 5V DC supply for the DAQ card is identical with the 12V DC connector...

In most cases, a 12V input will damage the power surge protection diode "D9" (near the power input receptactle), or the 12V DC supply will get damaged, but it'll usually protect the rest of the DAQ card. A description of the diode is found here (part number SMBJ5.0, a 5V transient voltage suppression diode).

What to do?

Check diode "D9" with an ohmmeter. If it's a short circuit (i.e. less than 5 Ohms), then please contact Hans to get the diode replaced soon.

GPS problems, e.g. no 1PPS pulse or no GPS data?

After power-up it will usually take approx. 20 seconds to 3 minutes for the GPS receiver to get a position and time fix (depending on satellite visibility). Then you should see the "1PPS" LED flashing in a 1-second rhythm (top LED between the main reset button and secondary 5VDC input receptacle). The GPS antenna itself also has a status LED which will flash in a 1-second rhythm either red (bad reception or initialization phase) or green (good, locked onto GPS satellites).

On the DAQ card, you can check the GPS status with command "DG" after you connected the DAQ card to a PC and run a terminal program (e.g. HyperTerminal). An example of the DAQ response with good GPS data is found here. Note, the time is displayed in UTC (Universal Time Coordinated) which is 8 hours ahead of Pacific Standard Time (winter) or 7 hours ahead of Pacific Daylight Savings Time (summer).

No GPS data at all or time/position not correct?

Try moving the GPS antenna to a location with better sky visibility.

1PPS LED not flashing, and "CPLD freq" value not 41666667 (+/-50)?

Probably, the special grey cable between GPS antenna connector and the DAQ card either has a loose connector or is damaged internally. This special cable has a 9-pin receptacle on the far end (where the GPS antenna is connected) with a small circuit board inside. We found that the cabling became loose in some of these circuits, probably caused by too much pull on the cable (e.g. when hanging the cable freely from a roof). In other cases, we found water collecting inside the connector housing.

We recommend:

• Avoid pulling on these cables at the far end. Best if you add additional strain relief on both sides of the 9-pin connectors.
• If the 9-pin connectors at the GPS end are exposed to weather, please make them weatherproof. E.g. plastic bag wrapped tightly with electrical tape. Or, better, shrink-wrap the connectors. We can help you with either methods.

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