Twenty years ago I bought my first multimeter a Chinese-made DT830D.I was not into electronics then.In fact it wasn't until rather recently that I started tinkling with circuits. It was more like the desire to learn electronics one day that made me buy it back then.
Anyway,that multimeter was still working until recently when it developed a problem-it could measure resistance.Here are the symptoms it had.
SchematicSchematic of a similar multimeter model DT830B here.
|the legendary Chinese multimeter|
- At first, it could not measure small value resistors like 10ohms.The meter was fluctuating around 10 dislaying 12 ,9,8,sometimes 10 ohms and never stabilizing.All the other measurements of bigger size resistors seemed fine.
- the diode meter did not work at all
- Later on it could measure resistance at all zeroing out the number on the LCD.
So,I decided to have a look inside.When I opened it a rather big scorched resistor could be seen right away.It measured 90K.
I did a net search and came across a post in a Russian forum.It suggested the resistor R5 should be replaced with a 1K value one.The model of the multimeter was the same but a much newer version with smds.
I replaced the resistor with the first 1K I could find and that was it!It worked!Now the old multimeter is working measuring resistance correctly.On top of that the resistor fixed and the diode function problem.I am not sure how the resistance and the diode functions are connected with this particular resistor.
replace the resistor in the images for a 1K new one.
|Here is the new 1K resistor in place.|