Hi there, recently I got a not that cheap chinese multimeter based on VC9805 schematic.
Unfortunately it doesn't measure correctly.
Here is an example:
Range | ~33mv | ~100mv | ~503mv | ~2V | ~3V | ~10V
200mv | 33------ | 101-------| - ---------| -------| ----- | -
2v------| 0.030---| 0.98------ | 504----- | 1.94 | - ---- | -
20v----| 0.01-----| 0.08 ----- | 0.48----- | 1.7-- | 3 ---| 10
200v---| 0 --------| 0 -------- | 0.03 ----- | 0 --- | 2.8 | 9.8
1000v-| 0---------| 0 -------- | 0 --------| 0---- | 1 --- | 8
range ohms
200---- | ---------| --------| ------- | ---------| 1.2
2k------ | --------| --------| ------- | 0.981 | 0
20k---- | 4.89---| --------| 2.15 | 0.96----| 0
200k-- | 4.7-----| 29.5--| 1.9-- | 0.8------| 0
2m---- | 003--- | 0.027 | 0------| 0-------- | 0
20m-- | 0------ | 0.01-- | 0------| 0-------- | 0
Both V and Ohm measures go through RS2 RS3 RS4 and RS5. All that resistors measure as shown on the schematic - 1k, 9k, 90k and 900k. RS6-9 are 1.75m, 2.95m, 1.75m and 2.95m or total of 9m ( while it should be 10m, but even with added 1M resistor, the measure pattern still stays the same ).
I also have measured the resistance of the paths for all V ranges between Rin and the corresponding resistor ( for instance range 20V - Rin <-> RS5xRS4 ) and all paths have almost the same resistance ( +/- 0.2 ohm ). These are the paths which go through the range selector knob. Also, the multimeter is almost brand new and no damage is visible on the contacting surfaces.
Rin is 1M
Any ideas what else to check?
p.s.
range | 1uf | 22uf | 10- | 1 ----| 0.47 | 10
200u--| 1.1 | 23.4 | 10.9| 1.1 --| 0.5 -| 0
20u---| 0.94| 19.3 | 8.52| 0.93--| 0.44 | 0.01
2u----| 0.95| ---- | ----| 0.945 | 0.448| 0.009
200nf-| ----| ---- | --- | ----- | -----| 9.1
20n---| ----| ---- | --- | ----- | -----| 9.15
The current measurements seem fine ( of course need calibration ).
Unfortunately it doesn't measure correctly.
Here is an example:
Range | ~33mv | ~100mv | ~503mv | ~2V | ~3V | ~10V
200mv | 33------ | 101-------| - ---------| -------| ----- | -
2v------| 0.030---| 0.98------ | 504----- | 1.94 | - ---- | -
20v----| 0.01-----| 0.08 ----- | 0.48----- | 1.7-- | 3 ---| 10
200v---| 0 --------| 0 -------- | 0.03 ----- | 0 --- | 2.8 | 9.8
1000v-| 0---------| 0 -------- | 0 --------| 0---- | 1 --- | 8
range ohms
200---- | ---------| --------| ------- | ---------| 1.2
2k------ | --------| --------| ------- | 0.981 | 0
20k---- | 4.89---| --------| 2.15 | 0.96----| 0
200k-- | 4.7-----| 29.5--| 1.9-- | 0.8------| 0
2m---- | 003--- | 0.027 | 0------| 0-------- | 0
20m-- | 0------ | 0.01-- | 0------| 0-------- | 0
Both V and Ohm measures go through RS2 RS3 RS4 and RS5. All that resistors measure as shown on the schematic - 1k, 9k, 90k and 900k. RS6-9 are 1.75m, 2.95m, 1.75m and 2.95m or total of 9m ( while it should be 10m, but even with added 1M resistor, the measure pattern still stays the same ).
I also have measured the resistance of the paths for all V ranges between Rin and the corresponding resistor ( for instance range 20V - Rin <-> RS5xRS4 ) and all paths have almost the same resistance ( +/- 0.2 ohm ). These are the paths which go through the range selector knob. Also, the multimeter is almost brand new and no damage is visible on the contacting surfaces.
Rin is 1M
Any ideas what else to check?
p.s.
range | 1uf | 22uf | 10- | 1 ----| 0.47 | 10
200u--| 1.1 | 23.4 | 10.9| 1.1 --| 0.5 -| 0
20u---| 0.94| 19.3 | 8.52| 0.93--| 0.44 | 0.01
2u----| 0.95| ---- | ----| 0.945 | 0.448| 0.009
200nf-| ----| ---- | --- | ----- | -----| 9.1
20n---| ----| ---- | --- | ----- | -----| 9.15
The current measurements seem fine ( of course need calibration ).
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