Genuine Dallas SRAM IC Chip DS-1225AD-150, Tek Part # 156-2991-00 Preloaded with Standard Calibration Data For Tektronix 2445B, 2455B, 2465B or 2467B Oscilloscopes REVISION DEC 15 2020 DS1225Y is no longer in Production, as such we use DS1225AD or DS1225AB which are still in production Tektronix 2400B series oscilloscopes with SMD Controller Board ( 671-0965-XX ) use a SRAM Memory chip to store all Calibration related parameters, these Chips have an internal Lithium battery keeping the data safe during absence of power According to Dallas Semiconductors datasheet Battery has a usable life span of 10+ Years When the battery fails, all calibration data are lost, and you will get a Test 04 XX boot error & a garbled display with ??? on the lower part of readout.
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