After years of trusty service my HP54601A scope died. Actually he didn’t die, he started to complain about it’s memory on power up. That made him useless. So time to unscrew the backside and see what’s inside.

This scope is well build and easy to dismantle. One large PCB on the bottom is all there is and you’ll directly spot the two types of memory used, a EPROM containing the main CPU software and a DS1220 (Dallas 16k Nonvolatile SRAM) to store settings. I trust the EPROM and don’t trust the DS1220 so much. The first line on the datasheet states “10 years minimum data retention in the absence of external power” and this scope is about 15 years old so I’ll start by blaming the DS1220.

On the internet there are tutorials on how to “repair” a drained DS1220 battery, just by opening it’s belly and replacing the Lithium battery. I’m not going this way since new DS1220’s are still available for cheap.

Removing the DS1220 is delicate job, it’s soldered directly on the PCB and there is hardly any room between the chip and the PCB. I used a scalpel to cut the pins between the chip and PCB and un-soldered the the pins from the PCB one by one. Removing the chip without damaging the PCB is easy this way. The new DS1220 is placed in a header so I don’t have to solder again over 15 years.

Will this do the trick? Will the memory error disappear? Yes, it did. Everything is set back to the default settings and calibration settings are lost. So next up is calibrating the HP54601 …