Another multimeter someone was throwing out, as it was dead. Since I am slightly sick and do accumulate all sort of test instrument garbage, I paid for this and got it home.
Just coz its cute and it will make total number of multimeters I have to 21. I liked the form factor and the bench meter appeal, but still it could be handheld.
So here is the original condition – the “Before”
And here is the “After ”
As expected, it was mainly a cleaning job for the switches and few resoldering around the main switch panel to get this back to working.
Here are the internals, very interesting design, and beautiful construction. Amazing industrial design.
Here its all in pictures.
To open remove the rear panel
Then remove the screw in the center. Next one to remove is the protection fuse for ammeter. Here it is, twist and take it out
Then you can gently slide the unit out
Disconnect the battery terminals
And you have access to the internals. Once you take off the 4 screws holding the LED panel, here is how it spread out.
From a repair perspective, for me proper cleaning was the first step, secondly re soldering switch contacts as I would not leave them, repeated stress does cause bad solder joints. Caps were in good shape, didn’t touch them.
Here are more pics.
Post cleaning, reassembled the unit and I have a very interesting problem. Autorange is not working. Further investigation narrowed it down to the root cause.
Auto range is working in resistance mode. Which means, its not an issue with autorange logic.
DC and AC Volt is working in manual range on ranged above 2V, which means DMM/ADC is all good.
So, I verified and confirmed that 2mV and 2V ranges are dead. So naturally when you auto range, it will try to start from lowest and climb up, since those 20mv and 2V ranges are dead, auto range will die there.
Attention goes in to input divider, which is not very easy in this, as its an autoranging meter, so FET switches are involved in the input divider.
Here is the schematic
And I discovered the most bizarre thing ever. One resistor leg is not soldered. It was lifted up and bend the other way up. It did not look like someone reworked it, as the board was clean, but not sure, they may have done a clean job. The resistor involved is R16, 47K/1W.
I am not sure who did it and why. I re-soldered it back to the board and all ranges started working, so do auto range. I didn’t want to blog it, but realized, this could be confusing, as by design, there are few resistors which are soldered but leads cut during factory calibration. It is mentioned in the schematic, top left corner. So may be will help someone who is facing this.
I didn’t get the original power supply, but any standard 5V should work, as I could decode this from the schematic. I used one of my own little 5V adapter. Remember -ve is the inner pin, +ve is outer sleeve.
The battery can be normal cell or rechargeable Ni-Cd. In case you are using Ni-Cd, remember the press the switch down behind the unit using some means. This connects the charger to the battery. This will be disconnected by default for normal non rechargeable battery operation.
Here is the battery charging control switch from the back of the unit.
which is accessible from the rear battery compartment. (Not sure if its the left hole or right..lol)
Here is the finished unit.
Check the hoodie, which can be pulled out, in case you are doing measurements in bright light or outdoors, it will help you to see the display properly.
Here is in my bench,
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