Faulty Brymen (857?)

[TroelsM]

Hi Guys.

First time poster, longtime watcher. Hope this is the right place to post.
I'm a experienced electronics engineer, but sadly with lack of time (and maybe talent  )

I rescued an Brymen from the dump at work and I'm pretty sure its a 857 model.

Visually it appears to in good condition, and display and buttons look good.

It can measure mV ( havnt verified precision, but it measures), but V and A shows OL in the display ( after a short flicker)

A quick look inside does not reveal anything burned.

I assume that the "measuring core" is good because its can measure mV, - but maybe that's a flawed logic?

I tried taking apart the function-selector-switch and all looks good.

I cant find any schematics or service manuals.

Any ideas? -it looks like a great meter, but I dont have the time to reverse-engineer something like that at the moment.

Kind regards TroelsM

[shakalnokturn]

I own a couple of these and could make comparative measurements (only) once you've spent some time deciding what interesting test points could be.
I don't know if calibration constants are stored in external EEPROM or internal to CPU on this model, if no one else out here has made dumps available I may also go to that bother.

You do not mention how it behaves for resistance and capacitor measurements.

Have you started with the basic checks that can tell you quite a bit on what's going on:
Link it up to another multimeter, measure input input resistance while cycling through voltage ranges and current ranges.
In Ohmmeter measure output voltage and current on different ranges.

Most handheld designs don't use the precision resistor network for the mV range so may be worth looking if that isn't broken.

[TroelsM]

Thank you for the kind offer, but Ii wont asku you to go through all taht trouble for me.

I tried measuring from inoput terminal to the precision resistor network, -assuming that there would some veldefined path from input terminal in Vdc mode.
My readings did not make much sense to me, but maybe Ii was looking for a lowish-value, and in reality theres a very high impedance?

Anywhos, not finding a clear path, I looked at the mode selector again. There is 2 decks of switches connected by a plastic part.
The switches must align and alsoe align with the plastic part for mode-selection to be stable.
Ii tried moving the plastic-part relative to the 2 switches and apparently that did make difference.

i looks like everything but the AC-ranges work now. - that would indicate a broken AC-coupling cap, but thats the last component I would normally suspect. Therefore Ii assume that this is also related to the mode selector somehow?

Ii have decided to leave it as-is for now. Ii have other meters for AC, and i will wait a little and see if the "fix" on he DC ranges is stable over time.

Kind regards TroelsM