Faulty Agilent U1241AN Multimeter with tiniest of leaking batterie damage - Page 1
Forum section: electronics / testgear

author: kblue
author_rank: Regular Contributor
timestamp: April 19, 2025, 11:15:49 am
content: Hello there!Scored myself something for repair/for fun. This multimeter suffered from leaking batteries but not that much as some other specimens shown in this forum. It was manageable or at least i think so. One push-button lost his contacts, two SMD-caps had grown crystals, one resistor of the 10M (5x2M) ladder developed a little bit of crystals but all of this is already successfully removed. The whole cleaning / brushing session took hours but under the microscope it looks good now.Turned the unit on, all segments are shown for a brief moment and without any input i got 0,0 mV (Auto-Range). At first, it was kinda odd that it stayed at nearly 0,0 +/- 0,3 mV ... other meters go haywire without shorted inputs due to high-imp. Tried to feed in 5 Volt and it showed me ... 6,0 mVSometimes 6,1 mV so ye, there is something off. After the ladder the input signal at V/Ohms/etc jack passes to two components:(1) through a 10k resistor to "OPA U340" which output is linked to a SMD cap ... so i guess, that's not the path of DC measurement(2) through a 1k resistor to "MAX4582" which outputs-switches branches of in all sorts of directions.I noticed between Pin 3 (Y - Input) and Pin 1 (Y0) of the MAX4582 the resistance was less than 2k. Which it is not between Y and all other Y... lets say "outputs". The other side with Pin 13 (X) and all "outputs" Pin 11, 12 + 13, 14 all are in the OL or MegaOhms. Compared to another MAX4582 on board, all pins are also in the MegaOhms or OL. Even Y and Y0, which is not the case with the first one. So i removed the chip and its still measuring around 1,8k between Pin 3 and Pin 1. Which i don't think it's normal.So the next thing i tried was giving 1 mV at one of the "outputs" where the chip was located. Because after the resistor ladder with 5V input i got around 1mV at the end. I was hoping one pin should be the "voltage measurement line" and the meter should show me something. Thing is ... it's reacting at like all the lines in different waysMayhaps my artificial input needs to be feed into multiple points at once? Could be the case if a Multiplexer/Switch was installed at my testlocation.Other things i tested:- Ohms was bad aswell (100 Ohm showed 90 Ohm ... way out of spec; 100k Ohm was OL)- Diode was "okayish"- Capacitortest wasn't able to measure anything- mA is spot on (its another jack)As i don't have any schematics, its kinda hard to follow the voltage-measurement line. The Main IC is some Samsung-Part. Next things to do would be to check more of the vias, but so far some spot-checking was good and testing random vias in the little area of the corrosion i had, there was continuity. Next step would be ordering some new MAX4582 or equivalent, because i'm pretty sure at least the one i removed is in no working condition.The attached pictures are with MAX4582 already removed (was also curios if corrosion was UNDER the chip ... which there was none). The two wires (red/blue) are just for testing purpose (6V). Some resistors lost their marking, this is due to some fine brushes for removing the little leaking battery damage that was left (the board already had a bath). As said, it wasn't much, i've seen way worse damage in other meters.Best wishes!

author: AVGresponding
author_rank: Super Contributor
timestamp: April 21, 2025, 09:08:56 am
content: Probably still worth giving it at least one overnight soak in 99% IPA, and baking it dry if you have the facilities (stick it in front of a fan heater if not, at a range where you could hold your hand without getting burned).

author: kblue
author_rank: Regular Contributor
timestamp: April 21, 2025, 12:07:56 pm
content: Will try that. Just a IPA bath or IPA bath with ultrasonic cleaner? I have a big one for that.But for now, waiting for a new MAX4582, as i am sure the old one is faulty (less than 2k between two pins which should be open/not switched without power/signal).

author: kblue
author_rank: Regular Contributor
timestamp: April 30, 2025, 01:52:45 pm
content: Cleaned the board and placed a new MAX4582 IC - the unit is now back in full working condition. The only odd thing is ... the last digit keeps bouncing around. Shorted input in DC shows 0,0 mV or 0,1 mV. Or a stable 5,000 VDC reference bounces between 4,999 and 5,000 VDC ... 100 Ohm precision resistor bounces between 99,9 and 100,0 Ohm - sometimes rapidly which makes "reading" the measurement kind of maddening. I compared the PCB of my unit with the PCBs i found in the web and it seems my unit comes with two trimmers near the replaced MAX4582 (which handles the input) while others have fixed SMD capacitors.I dont know if this is "normal behaviour" but it sure is confusing and my gut feeling tells me it has something to do with the trimmers (they might have changed values during the ultrasonic bath). But before that, i'll check the electrolytics they do report oddly (like 100 uF / 16 V reports as 167 uF with 5 Ohm ESR) but this could be due to being "in circuit".Apart from that, it seems to be working just fine.Best wishes!