2008. At that time, significant upgrades were made to the electronics. After the upgrade, the new phase of the experiment has been referred to as Super-Kamiokande-IV. SK-IV collected data on various natural sources of neutrinos, as well as acted as the far detector for the Tokai-to-Kamioka (T2K) long baseline neutrino oscillation experiment. SK-IV continued until June 2018. After that, the detector underwent a full refurbishment during Autumn of 2018. On 29 January 2019 the detector resumed data acquisition. Detector The Super-Kamiokande (SK) is a Cherenkov detector used to study neutrinos from different sources including the Sun, supernovae, the atmosphere, and accelerators. It is also used to search for proton decay. The experiment began in April 1996 and was shut down for maintenance in July 2001, a period known as "SK-I". Since an accident occurred during maintenance, the experiment resumed in October 2002 with only half of its original number of ID-PMTs. In order to prevent further accidents, all of the ID-PMTs were covered by fiber-reinforced plastic with acrylic front windows. This phase from October 2002 to another closure for an entire reconstruction in October 2005 is called "SK-II". In July 2006, the experiment resumed with the full number of PMTs and stopped in September 2008 for electronics upgrades. This period was known as "SK-III". The period after 2008 is known as "SK-IV". The phases and their main characteristics are summarised in table 1. SK-IV upgrade In the previous phases, the ID-PMTs processed signals by custom electronics modules called analog timing modules (ATMs). Charge-to-analog converters (QAC) and time-to-analog converters (TAC) are contained in these modules that had dynamic range from 0 to 450 picocoulombs (pC) with 0.2 pC resolution for charge and from −300 to 1000 ns with 0.4 ns resolution for time. There were two pairs of QAC/TAC for each PMT input signal, this prevented dead time and allowed the readout of multiple sequential hits that may arise, e.g. from electrons that are decay products of stopping muons. The SK system was upgraded in September 2008 in order to maintain the stability in the next decade and improve the throughput of the data acquisition systems, QTC-based electronics with Ethernet (QBEE). The QBEE provides high-speed signal processing by combining pipelined components. These components are a newly developed custom charge-to-time converter (QTC) in the form of an application-specific integrated circuit (ASIC), a multi-hit time-to-digital converter (TDC), and field-programmable gate array (FPGA). Each