EEVblog 121GW Multimeter Issues

[thm_w]

If the HY3131 DMM front end IC is non-responsive, I wonder if it gives these same results? Or if it shows some kind of error code.
Clearly the STM32 is running and responding.

[bdunham7]

It works 

I notice that it is warmer where you are then where he was.  Can you try putting it in the refrigerator overnight and then trying it the next day?

And if chilling it does induce the failure, could crystal X1 for U3 (the HY3131) not starting cause it to behave as shown?

[LampHead]

Having a similar problem with the 500mA input as well. When switching from Low_Z to Hz measurements, it gives a 'LEAD' alarm with the leads plugged in the COM and V terminals. If I plug a dummy lead into the 500mA terminal, the alarm goes away. I'm using the latest firmware 2.05, new 1.5V batteries, and I've cleaned the terminals. The meter has barely been used in the last 3 years.

Any ideas?

[EEVblog]

Having a similar problem with the 500mA input as well. When switching from Low_Z to Hz measurements, it gives a 'LEAD' alarm with the leads plugged in the COM and V terminals. If I plug a dummy lead into the 500mA terminal, the alarm goes away. I'm using the latest firmware 2.05, new 1.5V batteries, and I've cleaned the terminals. The meter has barely been used in the last 3 years.

Is it just a short beep and then goes away? i.e. it's not a problem yet, but indicative of a potential problem down the road.
You might be in a high EMF environment causing a false detection issue.

[LampHead]

Hey Dave

There's a persistent beeping with "LEAD" flashing on the screen. I'm not sure I have any major EMF emitters around, as I always use the DMM in the home office where I barely get any 4G signal

Do you reckon I need to replace the op-amp that senses the probes, or does it just need re-calibration?

Thanks

[EEVblog]

There's a persistent beeping with "LEAD" flashing on the screen. I'm not sure I have any major EMF emitters around, as I always use the DMM in the home office where I barely get any 4G signal
Do you reckon I need to replace the op-amp that senses the probes, or does it just need re-calibration?

In that case it's contamination of some descriptions. Could be hygroscopic moisture absorption into the connector plastics.
I did a video on this but can't find it right now.
Clean the PCB inside as a starter in case it's on the PCB.

[LampHead]

Ok Dave, I've cleaned the PCB and placed it in a bag with some silica gel. I'll provide feedback soon. Thanks!"

[jh15]

At least you didn't put in rice. Still love my 121gw.

[LampHead]

I'll be damned, it worked. I left it in the bag for weeks, pulled it out, and tried it in different modes — no beeping. Put all the covers back together and put it back in the bag again. Tried the DMM again today — still no beeping.
Winter humidity in my office was the issue, at least for me.

I think it might be useful to have an option to turn lead detection ON/OFF in a future firmware update. That way, if someone doesn't have time to dry it out right away, they can still use it.