Author Topic: MULTIMETER VOLTCRAFT VC650  (Read 1152 times)

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Offline lionelkjh

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MULTIMETER VOLTCRAFT VC650
« on: March 20, 2017, 04:34:20 AM »
Hello; I am currently restoring a multimetre voltcraft vc650, I have the schema, but I can not figure out which VDD and VSS should be, because they are not detailed (is it: -5V / + 5V ??). Can you help me? (I join the complete Shema with) Thank you for your answers
 

Offline JFJ

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #1 on: March 20, 2017, 05:00:41 AM »
From a data sheet for the KS57C2616 CPU:

VDD = 2.7V to 6.0V
VSS = Ground
 

Offline madires

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #2 on: March 20, 2017, 05:02:31 AM »
The charge pump for VSS is at the top left on page 2 (negative voltage), and at bottom right on the same page is the voltage regulator for VCC (U16, presumably 5V).
FidoNet 2:240/1661
 

Online Armadillo

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #3 on: March 20, 2017, 05:10:03 AM »
See picture attached
VDD = +5V
VCC = ~ +3V
GND = 0V
VSS = ~ -5V

« Last Edit: March 20, 2017, 05:17:00 AM by Armadillo »
 

Offline lionelkjh

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #4 on: March 20, 2017, 11:22:54 PM »
Hello; Thank you for this information. I did the measurements. VDD is at 5v, but vss is only -3.3v. I have checked the diodes D9, D10, they are good. I checked c11, c12 (replaced), and the voltage is still -3.3v. What do you think?? Can the circuit 74hc04 (u15) be involved ???
 

Offline madires

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #5 on: March 20, 2017, 11:49:19 PM »
-3.3V seems to be fine for Vss. The output voltage of such a charge pump can't go up to -Vcc. And the voltage drop by Q9 is maybe 0.2 or 0.3V, so Vcc is about 4.7V (in case Q9 is in saturation mode).
FidoNet 2:240/1661
 

Offline lionelkjh

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #6 on: March 27, 2017, 01:56:09 AM »
Hello, the voltage of -3.3v is not correct, it must be around -5v, it is missing -1.7v. Only the ohmmetre and diode tester parts are faulty. It is either too high or too low on a caliber of the ohmmetre. The entire circuit around the operational amplifier has been checked and checked, and there is nothing abnormal about it. An idea?? :palm:
 

Online Armadillo

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #7 on: March 27, 2017, 12:40:42 PM »
Use another meter to measure the voltage of the voltcraft at the probes, red to red, black to black.

1.0 put voltcraft to  diode mode - how many volt measured?

2.0 put voltcraft  to ohm mode - how many volt measured?

I think -3.3v should be fine due to loading of the circuit.
 

Online Armadillo

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Re: MULTIMETER VOLTCRAFT VC650
« Reply #8 on: March 27, 2017, 01:54:03 PM »
What exactly is the meaning of this "Only the ohmmetre and diode tester parts are faulty. It is either too high or too low on a caliber of the ohmmetre."??

Put a known ohm X ohm say 100 ohms or something, what is the reading?

Put a know diode X say 1N4148 or something what is the reading?

 


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