Details about Debugging Individual Bad Channels --------------------------------------------------- Original Rev. 22-AUG-2002 Current Rev. 19-OCT-2002 Please take responsibility for keeping the detailed recored of the debugging work that we do. This is going to be kept in the Cal Trig section of the web site. If you are not comfortable using SPIN to update and post this file then you may mail the updates to me and I will put it on the web. This record of debugging work is an ascii file, specifically not msword. Please use the standard TT coordinate system. Please organize the file in terms of TT's that we have worked on. Put these TT's in a rational order. Under each of these TT's keep track of: what was reported to be wrong with this channel, the tests and work we have done on it, any tests or work that needs to be done at the BLS end during the next available access, and any check that need to be made when the next set of Bob's plots become available. Debugging Individual Channels 1. Determine, is the problem in the L1 Cal Trig or is it in the cable between the BLS and the L1 Cal Trig or is it in the BLS. Check the L1 Cal Trig Electronics If the problem is in the L1 Cal Trig electronics, for now, we will assume that it is in the new analog electronics that is in front of the flash ADC on the CTFE card. We will test this part of the circuit using the hand pulser which will inject a signal into the BLS cable connector on the CTFE card and we will monitor the signal that goes into the flash ADC at the Lemo connectors on the CTFE card. The process is to compare the signal that we see on the Lemo output of the reported bad channel with what we see on a neighboring channel (same phi different eta) that is know to be a good channel. Using the hand pulser we can separately compare the EM+, EM-, HD+, and HD- signals. For channels where the reported problem is that you see only 50% of the expected signal, we should be looking for one side of the differential signal not working. Recall looking into a BLS cable connector on the CTFE card, the pinout is: HD- HD+ EM- EM+ Gnd Gnd Gnd Gnd The hand pulser injects a signal that is equivalent to about 30 GeV into the CTFE card at a rate of a couple of kHz. So clearly this is not a test that you can do during a run when the Cal Trig is being used for beam Physics triggering. Please remember, do not have the front door to the Cal Trig open for a long period of time. Absolutely never open more than 1 door at at time. Carefully close the door and verify that it is properly and fully closed. This is a must. Check the BLS Cable Unplug the BLS cable from the CTFE card and using the adaptor cable that lets you connect the BLS cable directly to the scope look at the two halves of the differential signal of the reported bad channel. Is there noise or oscillation on either side of the signals. Is either signal a flat line. Can you see the very small 132 nsec structure in the signal. Compare the signals to those of a neighboring phi. If either signal is a flat line then we what to check for shorts or opens in the BLS cable. Do this using the Fluke hand multi-meter and the adaptor cable that lets you plug the multi-meter into the BLS cable. Check for shorts to Gnd. If the problem is a short due to a center insulation pull back (a typical problem) then you may need to flex the cable near the connector to see the problem. I have also seen center conductor to center conductor shorts on these ribbon coax cables. The adaptor cable to the multi-meter lets you check for any of these conditions. If the problem is a center conductor open circuit then it is hard to see with the multi-meter because at the BLS end of the cable there is no DC current path (you are just looking at the output coupling capacitor on the BLS card). If we need to check for an open this is done by putting a target resistor pack that I have made at the BLS end of the cable and then looking with the multi-meter from the Cal Trig End. This resistor pack puts a different value resistor across each of the 8 coax cables in the ribbon. These resistors are all between 100 Ohm and 1 k Ohm. The values are marked on the pack. This range was picked to make it easy to identify the individual coax cables and thus straighten out any labeling problems on these ribbons. Note that the DC resistance of the center conductor on the long thin BLS cables is in the range of 10 Ohms. Recall the pinout of the connector at the Cal Trig end of the BLS cable. This is the view looking into the connector with top on top. EM+ EM- HD+ HD- Gnd Gnd Gnd Gnd Please remember, do not have the front door to the Cal Trig open for a long period of time. Do not open more than 1 door at at time. Carefully close the door and verify that it is properly and fully closed. This is a must. Check the BLS Card If the the L1 Cal Trig electronics looks OK and the BLS cable looks OK then the last thing to check is the BLS card. This should only be done in coordination with some one from the Calorimeter group. The exact procedure for doing this will have to be worked out with them. The first step is a visual inspection of the BLS card. Check to see that all the summers and driver hybrids are installed. Dean has told me that a missing input to a driver is a likely way to make it oscillate at times. Look to verify that the correct type of summer and driver have been installed. Verify that all the pins are in the socket, that things are not offset by one pin, and that the hybrid is not in backwards. We anticipate that a significant number of BLS problems will be solved just from visual inspection and correcting how the hybrids are installed or what type of hybrids were installed. If you do not see any problems from visual inspection, and we are convinced that there is a problem with the trigger pick off signal from the BLS card, then we will need to bring the BLS card out of the Collision Hall and put it in the BLS Trigger Pickoff Exerciser that is part of the 5k channel test setup. Record keeping. Clearly we need to keep track of what changes and repairs we have made. That's the only way we know what to look for on the next set of plots that Bob makes. With most of these repairs we do not know that we have actually fixed the problem until sometime later when we can check the next set of Bob's plots.