Close examination showed that the area around the solder pads had been masked off from the conformal coating but a small section of copper track from the pad for pin 11 to a via under the middle of the chip body had been dissolved away by electrolysis. With the hot air rework gun I lifted this chip off the board and found it to be wet underneath with a film of pale green liquid. With nothing to lose I decided to look at the most likely culprit – IC7, a 74HC132A (a quad 2 input NAND Schmidt trigger) surface mount IC on the back of the board under the LCD screen as this had a clear path to the batteries through a hole for the battery holder locating pins. All of this still failed to get the ‘Power’ button working, although all of the other functions of the meter seemed to be working normally. I had previously un-clipped the screen and was careful not to wet the rest of the board as I did not want to get water into any of the trimmers. My next suspicion was that some of the corrosive liquid from the cells had seeped in under the chips on that end of the board so I soaked just that end in warm water and detergent with some brushing, washed and soaked again in several changes of fresh water then into denatured alcohol and thoroughly dried with warm air. Using my cheapie multimeter, which I carry in the car glovebox, I was able to tediously trace a path from one of the switch contacts through a couple of resistors and diodes to the general area of IC7. The first thing I did was clean the switch contacts on the board and re-coat the button contact with a thin coat of powdered graphite rubbed in well but still no luck! So out with the magnifier and low power microscope to examine all of the tracks and components in the general area of the battery holder, but all looked good and well protected by the conformal coating. Fortunately the battery holder contacts cleaned up well with no signs of pitting or corrosion and I optimistically fitted new cells, but the meter powered up and presented a normal display as soon as I pushed the second battery into place and could not be powered down again using the ‘Power’ Button. I was rather surprised at this as I wrongly assumed that Duracells were reasonably leak proof. A couple of weeks ago it stopped working so I pulled the back off and found the batteries leaking and covered with a blue deposit on the ends. I have had it for 25 years after winning it for renewing my subscription to a well known Australian electronics mag and it has been an excellent piece of equipment which has worked faultlessly all that time. I came here seeking information on the HP 973A multimeter after mine recently stopped working. Often we care about <20V DC, you will likely find high end to be off spec, but at least the voltage that matters to you is accurate.Greetings All My first post on this forum. So if 3V is what you measure the most, set the calibration to 3V and adjust the pot to give you a 3V reading. * Determine the voltage that you care about, pick the point you use most often, then calibrate against that particular point. Then pick a calibration voltage which will allow both the high and low end to fall within spec. Now I am down to one of two ways: * You will need a voltage calibrator for the first approach, you first would map out the measured voltage on a graph across the entire measurement range. It used to drive me crazy trying to optimize the accuracy of a handheld DMM using the service manual, as the high end is always way off spec. For example, in DC alone, the Keysight 34401A has six separate gain adjustment across the voltage ranges, and 5 different zero adjustments for DC, for a total of 11. In a lab grade DMM where there are multiple adjustment points, there are multiple zero and gain adjustment for each range. Often, if there's a service manual, the calibration voltage is a single digit voltage for these meters, and not necessarily near the top of a range. Due to the non-linear nature of their A/D converter, and with the limitation to only one calibration point with the pot, when the low end is right, the top end might be off, and vice-versa. What you observed is very common with low end DMMs or older DMMs, where they calibrate using pots.