We have exchanged four crates in the following order: crate 10 and 9 in rack 9 (B14-19), crate 1 in rack 2 (B1-4 and one slot with B13) and finally crate 1 in rack 1 (B11-13).
Before the exchange we measured discharges in the old pick-up boxes. The OMs were disconnected whereas the HV cables were connected, but the HV was turned on to nominal values. Then we used the oscilloscope to estimate the noise level and measured the number of triggers during two minutes.
Thereafter we measured the gain and delay with OMs disconnected, and HV connected but turned off. To measure the gain we generated a 1 MHz and 100 mV peak-to-peak signal, damped 10 times with an attenuator, and fed it to the test input of each channel. For the delay time we used a square pulse, also damped 10 times with an attenuator.
Finally we reconnected the OMs and took waveforms of all channels with electronic readout. The settings on the oscilloscope was 500 ns/div and 50 mV/div.
When removing readout, OM and HV cables, we compared the labeling with the OM database and also wrote down the labels. Then we removed the old crates and installed the new crates. All new crates have separate power supplies, and there is room for 8 slots. Each new slot has 20 channels. The SWAMP cards are excessed from the front and the pick-up cards are excessed from the back. The power swith for the crate is located on the back of the crate, and each slot has its power switch on the front.
In order not to damage the SWAMPs, first turn on the crate, then the fan (if there is one), then the different slots and finally turn on the HV! Shutdown in reverse order.
We didn't have enough delay chips, and therefore we removed delay chips from the old SWAMP cards and put them in the corresponding new SWAMP card. When exchanging a SWAMP card, make sure you put in a working delay chip.
When a new crate was in place we once again measured discharges, then we set the gain of all channels to the old values. In case the channel used to be dead or empty (that is, didn't use to have a SWAMP card) we set the prompt gain to 1.0 V, and the delay gain to 0.5 V. Then we took new waveforms of all channels with electronic readout and compared with the old ones. As a final check we made a muon run and compared the ADC spectra with the ADC spectra before the exchange. When we were satisfied with how the new crated worked, we exchanged the next one.
In strings 11-13 we have used quad adapters to connect the square plastic connectors from the OMs to the quad socket on the pick-up boxes. It is very important to connect the right OM to the right channel, and to have the right polarity.
In the quad connector, even channels correspond to green-purple wires and odd channels correspond to blue-white wires. On the plastic OM connectors there is a mark one side, a line. When this marking is facing upwards (usually meaning that the cable label is facing downwards), the green respectively blue wire coming from the adapter should be to the left when you connect the adapter and the OM cable.
Some of the channels in strings 11-13 have low pass filters attached to their readouts, and in general the gain is set very high on these channels. With the new SWAMPs it might be possible to remove the filters and reduce the gain to nominal values (1.00 V and 0.500 V for prompt respectively delay), and still get the same effect, that is nice pulse shapes with lower noise level.
On the SWAMP cards there are three sets of dip switches. One set of four switches close to the delay chip (don't touch them!), another set of four and a set of two close to the readouts. The set of two switches control the upper limit of the bandwidth, and has two settings, both switches should be on (turned towards the readouts) which gives 15 MHz, whereas both off gives 8 MHz.
The set of four switches close to the readouts control the lower limit of the bandwidth, and these can be changed in order to remove low frequency noise. If 2,3,4 are on (turned towards the readouts) the limit is 50 kHz, if 2 is on the limit is 250 kHz, if 3 is on the limit is 150 kHz and finally, if 4 is on the limit is 75 kHz. Different SWAMP cards may have different settings and hence comparing settings between a good and a noisy channel might prove to be useful. Be aware of that a narrow bandwidth might give broader pulse shapes.
The remaining spare SWAMP cards have been put into previously empty channels. If the channel used to be empty according to the labels page, the SWAMP card can be removed and used as a spare. More SWAMP and pick-up cards will be sent from Stockholm.
The old SWAMP crates have been packed in four wooden boxes as follows:
| Box 1 | crate for strings 11-13 (used to be in rack 1) |
| Box 2 | crate for strings 1-4 (used to be in rack 2) |
| Box 3 | first crate for strings 14-19 (used to be in rack 9) and separate power supply |
| Box 4 | second crate for strings 14-19 (used to be in rack 9) and separate power supply |
The boxes are standing in the Jamesway outside MAPO. They are sealed and ready to be shipped to Stockholm in case it turns out that they are not needed.