Gossen Metrahit X-TRA troubleshooting

[giosif]

Hello,

I've recently acquired a Metrahit X-TRA which was not working due to battery leakage.
I've opened the meter and cleaned the PCB as best I could (it involved desoldering a few components, including the main IC, neutralizing with vinegar, washing with distilled water, etc.).
Now, I've re-soldered all components which had been removed and powered on the meter.
However, the meter would briefly turn on, try to autorange, then display "OFF" and turn off.
If I press the power button again, the same sequence happens again.
One thing I did notice, though, was that, while the meter is trying the autoranging, the LCD is also showing an empty battery for the battery level indicator.
So, I am guessing the meter cannot sense the battery level and thinks the batteries are almost empty, so it shuts down.

But I'm having trouble understanding which part of the circuit handles this battery level sensing, so I was wondering if someone here with experience on these meters could provide some hints/clues where to look.

Thanks!

[giosif]

I like seeing pictures when reading other people's repair threads/questions, so I'm providing a couple for mine.
The first one is before doing any clean-up (but after removing the battery terminals), while the second is how it looks today.

[retiredcaps]

I suggest finding out what the current draw is first.  Datasheet at

http://www.farnell.com/datasheets/42306.pdf

says 200 hours battery life using 2AA (3V).  To make it simple, assume AA have 2000mAh (like an Eneloop).  That suggests current draw should be around 10mA when operating normally.  If it's well above 10mA, then you might a have short somewhere or an open trace due to the battery leakage.

This meter uses the MSP430.  Find it's datasheet and look at how it sources Vcc.

[Mechatrommer]

i did clean mine and it still didnt turned on. the trick is after installing battery and leave it for like half an hour or couple of minutes, it turned on again and work fine. maybe something inside needs charging for a moment after no battery for long period, ymmv...
https://www.eevblog.com/forum/repair/gossen-metrahit-x-tra-m240a-dead-battery-leak-repair-help/msg2858022/#msg2858022

[giosif]

Coming back to this repair attempt after a long pause.
Apologies for the lack of response so far!

I checked current consumption for the meter and it looks to be within expected values.
Then, I checked several aspects of the MSP430: voltage supplies, ground connections, voltage reference output, crystal oscillators, battery voltage (that's on pin 5, BTW), RESET pin.
All checks out ok (I have an otherwise working Metrahit ISO with a cracked display which I used as reference).
Yet, the MSP430 still cannot detect the battery level properly (sees it as batteries depleted) and shuts down immediately.
Another interesting aspect is the meter display is constantly showing "IR" (normally used when the IR communication is enabled), even when powered off (but with power provided to the meter at the battery terminals).
The up and down arrows next to the "IR" text never come on, though.
So, I am inclined to think there is a problem with the MSP430 itself, in the sense that the voltage at pin 5 does not reach the internal ADC or the ADC itself is dead, which makes it unable to detect battery level and powers off. 
If only I could trick it into thinking the battery level is not so low or ignore the battery level check altogether...

Ah, and I did let the meter sit with power applied for 30+ mins, but nothing changed, I'm afraid.

If anyone has any suggestions, I would appreciate your input.
Otherwise, if someone happens to have a non-working X-TRA, I would be interested.
Thanks!

[giosif]

Another update on this - out of desperation and because I would really like to get this meter working, I took a more drastic approach and desoldered all the components acting as the glue logic between the digital / processing side and the analog side:
  * the HCT573 latch IC
  * the 3 x SN74LVC2T45 bus transceivers ICs
And, since I was at it and I had noticed that one of its pins was looking a bit dull (i.e. affected by corrosion), I also desoldered the custom ADC IC.

Interestingly enough, when I now power on the meter, it stays on.
It is not displaying any reading values, but that's expected in my mind, since it is not receiving such information anymore.
Also, the battery level is still showing empty.
But I can now go in the menu and get/set parameters, such as turning the always-on IR off (which worked).
As a side note, checking in the menu, even here the battery voltage is shown as 0.00V.

As a next step, I am looking to replace the latch and bus transceiver ICs with new ones.
In the meantime, reading the thread started by Dachpappe (https://www.eevblog.com/forum/repair/metrahit-pro-leaked-battery-repair-attempt/), I am checking connectivity between the bus transceiver ICs and the ADC IC.
I was able to confirm connectivity for 2 out of 3 ICs, but I need help with the 3rd.

Would anyone with an X-TRA or Pro meter help me determine where the pads in the light-green rectangle in the below picture are going, please?
I would normally check this on my Metrahit Iso, but that doesn't have a 3rd IC.

Thank you!

PS: Thank you, Dachpappe, for the description of your repair and I hope you don't mind me borrowing one of your photos.