CDC 12 12 2007
Interposer, preAmp, and signal cable
The new preAmp, the interposer, and the signal cable arrived at CMU. The first test that was performed was to apply 3.2 V on the preAmp board without anything connected to it: the board drew a current of 280 mA, this is ecact the current that is specified, good! After connecting the signal cable to it the current that was drawn doubled, not so good. It turned out the the piece of signal cable sticking out of the connector was touching the heat sink and making shorts. After cutting off this piece of cable the preAmp was again drawing 280 mA.
Channel 1 and 2 of the signal cable were connected to our postAmp and all the other channels were left open. When the preAmp is NOT connected to the HV distribution board a noise(?) signal can be observed on the scope (shown in figure 1).
When connected to the HV-distribution board the output signals looked like an 10 MHz oscillation. The signal seen on the oscilloscope is shown in figure 2.
This does not look like CDC signal. Another short was expected.
After inspecting the preAmp visually a short was found on the output connector: it was soldering sitting between to pins. This soldering was easy to remove. However, it did not improve/change the situation. After this the signal cable was checked for shorts - no shorts were detected. Then the signal cable was connected to the preAmp and the resistance was measured between OUTA and OUTB:
- ) 16 channels had a resistance of 950 Ohm -> these are the populated channels (#1-8 and #17-24)
- ) 7 channels were open -> these are the not populated channels (#10-16)
- ) 1 channel was shorted -> #9
At this point Fernando was contacted: he said that the channel #9 should not be shoted but that this should not influence the proper working of the preAmp. He suggested to terminate the populated channels that are not read out with 100 Ohm, this was done with no result (2 channels were connected to the postAmp, all the other channels except the not populated ones were terminated with 100 Ohm including the signal IN channel was terminated, the not populated channels were left open). After this I soldered all populated channels to the connector that goes to the postAmp, left the signalIN channel terminated and again looked at the scope: no change.
Pedestal measurement
A pedestal measurement was done with the pre-amplifiers not connected to the CDC. The width of the pedestals is around 10 ADC-channels. The width of the pedestals (with common mode noise subtraction) of the whole system is 40 channels. The width of "raw" pedestals is 150 channels
