tl;dr
multimeter METEX M-3850D
AC rail broken
open shows this:
20210901_154614.jpgprobing 230v50Hz shows this:
20210901_154404.jpgany ideas?
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Hello,
So i was looking around the web for help regarding an old metex i found in my fathers attic.
Im not that deep into electronics, so it is half a learning exercise for me, and half a repair project.
okay, so the problem is this:
I found it already broken, so i dont know how it broke.
Current 4mA, 400mA, 20A measurements: work fine(ish), as far as i can test.
TEMP: i dont know.
fHE: i dont know.
CAP: doesnt work, but i did parasitized it. and i dont really care for it, and it is on a different pcb. I will fix it when/if the rest is functional
DIODE: doesnt work
OHM: ok
LOGIC: ok
FREQ: ok(ish) well it gives me 50Hz when i plug it to the wall socket
VOLT: DC works fine (as far as i can test it, witch is 0-30V)
and AC doesnt work, but shows values, only very, very small.
As i said, im not really that deep into electronics. Well, i suppose im not totally useless, but this task makes me confused. Im basically sure of nothing. I dont have a proper schematic. the one i found is crap. Blurry. Half the values are unreadable or missing. And its not the right revision date. I found the part list, but its a different revision date too, so there are differences between schematic and the part list, and the pcb. and on top of that, the pcb is old and it was mangled before. there are tht resistors soldered here for testings, apparently im not the first fool to try to fix this thing.
voltcraft_dmm-3850d.pdfso... at first i thought that i'll brute force it, meaning, i'll test all the parts brainlessly with the part list and schematic. Few resistors were shot, so i swapped them, and that fixed the DC function, witch wasnt working at the start. Next i tested the op amps. As far as i can tell, they are fine. I dont think the main uCs are bricked, since most functions are working fine(ish). And screen is working fine. So now i started testing the converter on EAO and EAI pins on the MAX 134.
While probing the wall socket i get this from the EAO:
20210901_154806.jpgbut nothing comes back to the EAI. I dont have much experience with acdc converters, but i assume, something should be coming back?
Well, if someone with some skill could look at it and give me a pointer or two, that would be greatly appreciated