This document as a MS-word file:maintenance.doc
The swamp system consists of two functional parts: pick-up modules and swamp modules. Both types of modules are placed in frames each containing 20 modules. The frames are mounted into the crates in slots in the front and in the rear so that corresponding frames connect in the middle. There are a number of connectors in the signal path: OM connectors and HV connectors feeding the pick-up modules. Pick-up module connectors (red) feed pick-up output signals to the mother boards (upper and lower) of the pick-up frame. The signals from the upper mother board are transferred to the lower mother board via ribbon cables where they are funneled through a combined frame pick-up connector. This connector connects to the swamp frame connector at the swamp frame mother board. There is one swamp connector for each swamp module (20) on the swamp mother board. Thus each swamp system slot contains the following parts:
OM connectors (10 quad connectors or 20 HV-connectors)
HV-connectors (20)
Pick-up modules (20)
Pick-up module connectors (20)
Pick-up mother boards (2)
Pick-up frame connector (1)
Swamp frame connectors (1)
Swamp mother board (1)
Swamp modules (20)
This section describes observed faults.
There are three types of OM connectors: quad (string 14-19), block (11-13) and co-axial (the rest). Here we have observed errors in the quad connectors causing both breaks and shorts.
No observed faults
Two types of errors have been observed. Increased signal noise and capacitor shorts. Both require module changes.
These may come lose causing the signal to disappear. The noise level remains the same, however.
The upper pick-up mother board is connected to the lower pic-up mother board via soldered ribbon cables. The lower one contains the pick-up frame connector. No major faults.
No observed faults
No observed faults
No observed faults
Several fault modes exists:
failing prompt amplifier,
failing delayed amplifier,
failing adjustment of prompt amplification
failing adjustment of delayed amplification
suseptibility to sinus noise
All taken care of by replacing the swamp module.
A HV error is signaled by the 1458 or a zero-voltage was forced by the 1440. Appart from an actual fault in the HV distribution system this can be caused by shorts in the pick-up module or in the OM connector. Remove OM-connector and check if the short remains. If not check connector. Otherwise replace the pick-up board or replace the malfunctioning component. The cause is probably large leakage in one of the 10 capacitors in the capacitor bank. This can be checked by turning off the HV and probing the resistance of the HV input (should be infinite) when the OM connector is removed.
If the prompt signal is missing check the delayed signal or vice versa. If one of them works the error is in the swamp board. If none of them works there are several possibilities. First check the output noise level. If this is unnaturaly low the cause is probably a swamp error.
If the noise level is normal the reason may be insufficient HV to the PMT. A short may have caused the HV supply to turn off (3.1). There may also be a break in the OM-connection. If the 1458 HV-supply is used, check the current. If this is exceptionally low, the resistance ladder in the PMT base is probably not connected. This can also be checked by measuring the resistance between opposing pins in the OM-connector - should be in the range 1 - 5 Mohm.
Excessive noise or sensitivity to interference may be removed by changing the pick-up module.
Other errors reported include: a break in a filter inductor in a pick-up module (probably caused by a previous capacitor short) and a singal line in a pick-up mother board shorted to the ground plane due to faulty soldering.