Electronics > Repair

Another Metrahit Pro with leaked batteries - repair attempt

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AlphaBravo:
No need to apologize shakalnokturn. I take what I can get :)
The diode you shared does seem to fit! Many thanks for the suggestion. I'll look into it and try to find an equivalent one around the office.
As for the function linked to the cap: it is the continuity/diode measurement function. Let's see if I can get this last piece of the puzzle.

hefferlump:
Hi,
I have a Metrahit AM Pro (M242A) that developed a fault in the same manner that you describe. It could be that the batteries leaking and the subsequent damage was not causal of the fault you describe - I can easily understand leaving the multimeter closed away in a draw when it stops working!

Something that might be helpful - on the device I have, the IC that is covered by the black and white label in the photographs you have uploaded (which has "3-603-415-01" or similar written on it) is a Fortune Semiconductor  [FS9704B][/https://www.ic-fortune.com/upload/Download/FS970X-DS-44_EN.pdf] - a DMM analog front end chip. As I was working through trying to source the fault, I figured I'd check the analog inputs to that IC, check the voltage reference and hope to chase the fault out. From the datasheet, pin 34 is the voltage reference for the internal ADC for example.

Unfortunately, the device suddenly started to work again... I noticed there's a AD 5231B, a digital potentiometer in the analogue front end. Makes me suspicious of a firmware issue. I had left the batteries out of the device for a considerable period of time however so I had assumed any state would have been reset.

AlphaBravo:
Hi,

First of all, I'd like to apologize for the hiatus in updates since March.

Since then, I got contacted by a little bird which was kind enough to inform me that the components I had mentioned on reply #8 were the following:

* Diode is a TS4148-0805
* Capacitor is a LDECC2470KA5N00 with 47nF
This same bird left some warnings as well:
"Be very careful when soldering these caps. The melt extremely fast. Use leaded solder and turn your iron down juuust until the solder melts."

Thank you Mr. Bird for your kind hints!!

I duly applied these fixes but without any success with respect to the reported behavior (original post). On the other hand, I must admit these fixes made the multimeter more stable. By this I mean, the initial behavior is always reproduceable and not sometimes hidden by power or other unknown faults.

As to what hefferlump just wrote:
I hope my device also starts working again just as suddenly, but I am not too hopeful.
I'll attempt the approach you suggest and come back here with any conclusions/fixes that I might come across.

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