Author Topic: Metex MS-2000.  (Read 17408 times)

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Offline jstanchevTopic starter

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Metex MS-2000.
« on: October 13, 2015, 10:45:59 am »
My Metex MS-2000 stop to work in DMM mode. :'( 
In DMM mode can't find zero. Value moving and don't set to zero.   |O
For analog to digital conversion use MAX134CMH.
I am looking for a service manual or circuit for my Metex MS-2000 DSO.

Can anyone help with this?

Greetings.
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #1 on: October 13, 2015, 10:08:04 pm »
1) Was there an oops moment with this meter?  For example, did you have the meter on ohms while trying to measure mains ACV (240V) by accident?

2) If you short the probes and set the knob to DCV, does the meter show 0.00 VDC?

3) Does the meter show open circuit when set to resistance with the probes not touching anything?

4)  If you short the probes and set the knob to ohms, does the meter show 0.00 ohm?

5) Clear focused pictures of the inside pcb would help us.

6) Does the scope work?
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #2 on: October 14, 2015, 10:07:35 am »
Hello retiredcaps,
Thank You very much for help.
Answers:
1. No, just stop to work correct. I haven't accident.
2. Set the function on DC Voltage and short probe, meter doesn't show 0.00 V DC.
    Set the function on AC Voltage and short probe, meter doesn't show 0.00 V DC.
    Set the function on Diode TEST and short probe, meter doesn't show 0.00 V DC.
    Set the function on Continuity and short probe, meter doesn't show 0.00 V DC.
3. Set the function on Resistance and open probe, meter show around 4.6 MOhm.
4. Set the function on Resistance and short probe, meter show 0.0 Ohm.
Resistance work correct.
5. Pictures PCB: http://postimg.org/gallery/3cdgrg2lw/
6. Yes it's work.
Connect red probe to scope plug W/F and see follow pictures:



Short probe and i see follow picture:


Disconnect red probe from W/F and see follow picture:


This isn't problem for scope, work correct.

Greetings.
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #3 on: October 14, 2015, 03:32:58 pm »
7) Using another multimeter, what is the input impedance of the MS-2000 when it is turned on and set to DCV?  On most meters, it should be around 10M ohm.

8] What reading do you get when you short the probes when the MS-2000 is set to DCV?  Is this reading steady or it is fluctuating?  You say it is not 0.00, but what is the actual reading?

9) In the attached picture, I marked the following components.  For the following, you can measure them all "in circuit".

a) R65 (green arrow) looks like brown black red (1k ohm), likely a fusible resistor.  With another meter, what is the reading?
b) 2 blue colored PTCs (blue arrow).  Each should read between 500 and 1500 ohms. With another meter, what is the reading of each?
c) spark gap (white arrow).  Each should read open circuit with another meter set to measure its resistance. With another meter, what is the reading of each?
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #4 on: October 14, 2015, 06:26:16 pm »
7. Input impedance isn't stable it is fluctuate:
on range 400mV is from 1.4 to 3.1 MOhm
on another range is from 13.5 to 15 MOhm

8. Voltage is fluctuating always.

9a. Resistor colors are brown, black, brown (100Ohm) i measure 101Ohm.
9b. I measure two PTC without desoldering from PCB and value are 1.3 and 1.7kOhm. Tomorrow i will desoldering and will check again.
9c. Two spark gap have resistance around 57MOhm.

P.S.
Before few days i find circuit on METEX DG SCOPE 20Mhz and i see that DMM part is the same on my METEX of 95%. See page 19 Analog DMM Part.
http://www.produktinfo.conrad.com/datenblaetter/125000-149999/126560-sp-01-en-DG_SCOPE_20MHZ.pdf
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #5 on: October 14, 2015, 06:37:12 pm »
9b. I measure two PTC without desoldering from PCB and value are 1.3 and 1.7kOhm. Tomorrow i will desoldering and will check again.
PTCs are likely good.  Leave them in there for now.

Quote
9c. Two spark gap have resistance around 57MOhm.
Desolder both spark gaps and retest your meter to see if it works.  Measure both spark gaps out of circuit and report your reading.

Quote
Before few days i find circuit on METEX DG SCOPE 20Mhz and i see that DMM part is the same on my METEX of 95%. See page 19 Analog DMM Part.
http://www.produktinfo.conrad.com/datenblaetter/125000-149999/126560-sp-01-en-DG_SCOPE_20MHZ.pdf
I will download and look later.
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #6 on: October 14, 2015, 07:15:10 pm »
If the schematics are somewhat close, the PTC is 1.5k ohm so your readings of 1.3k and 1.7k are likely good.

The spark gap is AG20P (datasheet attached).  If I'm reading it right, the insulation resistance is 10000min [Mohm] or 10G ohm.  This suggests the spark gaps you measured are suspect and may be bad.

The meter will work with the spark gaps removed, but you won't get any input protection.  If the meter is fixed, you can then order replacements.
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #7 on: October 15, 2015, 12:42:12 pm »
Today desolder two spark gaps and situation is the same. Voltage fluctuate again.  :'(
Measure spark gaps and resistance is over 60MOhm. Maximum range of another DMM is 60MOhm.
« Last Edit: October 15, 2015, 01:30:02 pm by jstanchev »
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #8 on: October 15, 2015, 06:57:54 pm »
Okay, let's try this.

The MAX134 IC pinout is attached.  Pins 18 through 22 is where the input divider readouts are.

10) Put your meter on DCV.  Short Volt to COM using a shorting plug or aligator clip.  Using another meter, measure pins 18 through 22 and report your readings for each pin.

11) Put your meter on DCV.  Use a CR2032 cell or 3V source and feed it into the MS-2000.  Using another meter, measure pins 18 through 22 and report your readings for each pin.

12) With the two spark gaps removed, do those spark gap solder pads read open circuit?
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #9 on: October 15, 2015, 07:05:49 pm »
7. Input impedance isn't stable it is fluctuate:
on range 400mV is from 1.4 to 3.1 MOhm
on another range is from 13.5 to 15 MOhm
The above is problematic.  The input impedance should be stable.  A pcb with contamination could be a cause of the instability?
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #10 on: October 15, 2015, 09:54:59 pm »
I don't have a lot of knowledge or experience on relays, but if the readings on pin 18 and 22 are not what I expect, then
one or more of the relays could be bad?  Perhaps there is leakage current or one is intermittment?

I'm not sure how to properly test one though?  Datasheet attached.
 

Offline ModemHead

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Re: Metex MS-2000.
« Reply #11 on: October 16, 2015, 02:05:51 am »
Yes, the input impedance looks like a problem.  Normally there's no problem measuring the dc resistance of the front end of a working powered-up meter, but if there's current leaking in somewhere, it will throw off the measurement.  Reversing the leads will show inconsistent readings.  You may even be able to measure a voltage on the input jacks of the problem unit with a regular 10Meg DMM.  As mentioned, often the root cause of the current leakage is PCB contamination from electrolytic caps, batteries, or flux residue.
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #12 on: October 16, 2015, 05:20:16 am »
As mentioned, often the root cause of the current leakage is PCB contamination from electrolytic caps, batteries, or flux residue.
There certainly is a lot of old flux residue left on the pcb (via high resolution photos).

13) Did the MS-2000 develop this fluctuating voltage problem over night?  Or has this problem been around for a while?
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #13 on: October 16, 2015, 10:47:04 am »
10. Results are:
Range 400mV
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm - 125 mV - stable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 4V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm -  from 44 to 99 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - from 44 to 99 mV - unstable
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 40V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm -  from 2 to 17 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - from 2 to 17 mV - unstable
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 400V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm -  from 0.3 to 2.4 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - from 0.3 to 2.4 mV - unstable
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 1000V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm -  0 mV - maybe unstable but voltage and difference are very small i can't measure accurate
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV - maybe unstable but voltage and difference are very small i can't measure accurate

11. DC - 3 V and results are:
Range 400mV
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm - 126 mV - stable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 4V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm - from 215 to 250 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - from 215 to 250 mV - unstable
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 40V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm - from 34 to 44 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - from 34 to 44 mV - unstable
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 400V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm - from 5.2 to 7 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - from 5.2 to 7 mV - unstable
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0 mV

Range 1000V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm -  from 1.3 to 1.5 mV - unstable - voltage and difference are very small i can't measure accurate
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - 0 mV
Pin 20 on your picture, page 19 - pin 26 - 101 kOhm - 0 mV
Pin 21 on your picture, page 19 - pin 27 - 10 kOhm - 0 mV
Pin 22 on your picture, page 19 - pin 28 - 1 kOhm - 0.5 mV - maybe unstable but voltage and difference are very small i can't measure accurate

12. Results are:
Range 400mV - resistance is from 1.4 to 3.1 MOhm
Range 4V - resistance is from 13.5 to 15.1 MOhm
Range 40V - resistance is from 10.4 to 10.7 MOhm
Range 400V - resistance is from 9.9 to 10.2 MOhm
Range 1000V - resistance is from 9.94 to 10 MOhm
When i Power off METEX from Power button resistance slowly(2 min) raise to 38MOhm.
Set the function on Resistance and open probe, meter show around 4.6 MOhm again.
When on display blink indicator for low battery then stable resistance 4.6MOhm began to fluctuate.

13. The problem began before two month and continuous still.
I think that i have a problem with voltage of DMM-P(page 19 Analog DMM Part) and then maybe with DVDD. DMM-P is come from Power part but i haven't power part circuit for my meter. This from page 21 Power Part isn't the same. Maybe someone capacitor in Power part.
 

Offline Fraser

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Re: Metex MS-2000.
« Reply #14 on: October 16, 2015, 01:49:29 pm »
Just for info, these MS-2000 units suffer power supply problems. It is standard procedure on these to look for issues on the output of the DC-DC converters. IIRC there are several such converters in this model.

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Offline retiredcaps

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Re: Metex MS-2000.
« Reply #15 on: October 17, 2015, 03:56:26 am »
Just for info, these MS-2000 units suffer power supply problems. It is standard procedure on these to look for issues on the output of the DC-DC converters.
I'm not familiar with the Metex MS-2000 at all and was not aware of its power supply problems.

If the power supply is suspected, checking pin 7 (V+) on the MAX134 would be the next step.  It should be stable and steady at 5V or 9V according to the datasheet.  A scope should also show low ripple on this V+ rail.
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #16 on: October 17, 2015, 04:04:01 am »
10. Results are:
Range 400mV
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm - 125 mV - stable
From the datasheet and schematic, the 10M ohm resistor is not involved when the meter is in 400mV range.  It is, however, used in the 4V to 1000V range.

So I'm not sure if the 125mV reading on the 10M ohm input pin is correct or not when the MS-2000 is set to 400mV.

Quote
Range 4V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm -  from 44 to 99 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - from 44 to 99 mV - unstable
With the probes shorted (0V) and the MS-2000 set to 4V range, the input divider should show 0.0mV on the 10M and 1.11M pins.  Since there is voltage on those pins, something is definitely wrong.

Quote
11. DC - 3 V and results are:

Range 4V
Pin 18 on your picture, page 19 - pin 24 - 10 MOhm - from 215 to 250 mV - unstable
Pin 19 on your picture, page 19 - pin 25 - 1.1 MOhm - from 215 to 250 mV - unstable
With a 3V source and the MS-2000 set to the 4V range, the input divider should show a steady and stable 300mA on the 10M and 1.11M pins.

Quote
12. Results are:
Range 400mV - resistance is from 1.4 to 3.1 MOhm
Range 4V - resistance is from 13.5 to 15.1 MOhm
Range 40V - resistance is from 10.4 to 10.7 MOhm
Range 400V - resistance is from 9.9 to 10.2 MOhm
Range 1000V - resistance is from 9.94 to 10 MOhm
Are the above measurements the spark gap solder pads?

Quote
Set the function on Resistance and open probe, meter show around 4.6 MOhm again.
When on display blink indicator for low battery then stable resistance 4.6MOhm began to fluctuate.
I saw that earlier, but didn't comment on it.  With open probes, it should show open circuit instead of 4.6M ohm.
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #17 on: October 18, 2015, 08:22:58 pm »
Quote
Are the above measurements the spark gap solder pads?
I am not solder spark gaps yet.
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #18 on: October 18, 2015, 10:24:58 pm »
Quote
Are the above measurements the spark gap solder pads?
I am not solder spark gaps yet.
No, I don't want you to put the spark gaps back in.  I just want you to measure the empty solder holes where the gaps were and report the resistance of both of them,
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #19 on: October 20, 2015, 11:37:35 am »
Results are:
Power on METEX. Change to DC and range 400mV. Power off METEX.
Black probe on 1, red probe on 2.
SG1 on PCB and circuit(page 19) - resistance is 10 MOhm
Black probe on 2, red probe on 1.
SG1 on PCB and circuit(page 19) - resistance is 10 MOhm
Black probe on 1, red probe on 3.
SG2 on PCB and circuit(page 19) - resistance is 10 MOhm
Black probe on 3, red probe on 1.
SG2 on PCB and circuit(page 19) -  resistance is 10 MOhm

Power on METEX. Change to DC and range 4V or 40V or 400V or 1000V. Power off METEX.
Black probe on 1, red probe on 2.
SG1 on PCB and circuit(page 19) - resistance is 40.7 MOhm
Black probe on 2, red probe on 1.
SG1 on PCB and circuit(page 19) - resistance is 49.2 MOhm
Black probe on 1, red probe on 3.
SG2 on PCB and circuit(page 19) - resistance is 40.7 MOhm
Black probe on 3, red probe on 1.
SG2 on PCB and circuit(page 19) -  resistance is 49.2 MOhm

Power on METEX. Change to DC and range 400mV.
Black probe on 1, red probe on 2.
SG1 on PCB and circuit(page 19) - resistance is from 1.4 to 3.1 MOhm
Black probe on 2, red probe on 1.
SG1 on PCB and circuit(page 19) - over 60 MOhm
Black probe on 1, red probe on 3.
SG2 on PCB and circuit(page 19) - resistance is from 1.4 to 3.1 MOhm
Black probe on 3, red probe on 1.
SG2 on PCB and circuit(page 19) - over 60 MOhm

Power on METEX. Change to DC and range 4V.
Black probe on 1, red probe on 2.
SG1 on PCB and circuit(page 19) - resistance is from 13.2 to 14.2 MOhm
Black probe on 2, red probe on 1.
SG1 on PCB and circuit(page 19) - resistance is from 7.8 to 8.8 MOhm
Black probe on 1, red probe on 3.
SG2 on PCB and circuit(page 19) - resistance is from 13.2 to 14.2 MOhm
Black probe on 3, red probe on 1.
SG2 on PCB and circuit(page 19) - resistance is from 7.8 to 8.8 MOhm

Power on METEX. Change to DC and range 40V.
Black probe on 1, red probe on 2.
SG1 on PCB and circuit(page 19) - resistance is from 10.4 to 10.6 MOhm
Black probe on 2, red probe on 1.
SG1 on PCB and circuit(page 19) - resistance is from 9.6 to 9.8 MOhm
Black probe on 1, red probe on 3.
SG2 on PCB and circuit(page 19) - resistance is from 10.4 to 10.6 MOhm
Black probe on 3, red probe on 1.
SG2 on PCB and circuit(page 19) - resistance is from 9.6 to 9.8 MOhm

Power on METEX. Change to DC and range 400V or 1000V.
Black probe on 1, red probe on 2.
SG1 on PCB and circuit(page 19) - resistance is 10 MOhm
Black probe on 2, red probe on 1.
SG1 on PCB and circuit(page 19) - resistance is 10 MOhm
Black probe on 1, red probe on 3.
SG2 on PCB and circuit(page 19) - resistance is 10 MOhm
Black probe on 3, red probe on 1.
SG2 on PCB and circuit(page 19) - resistance is 10 MOhm
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #20 on: October 20, 2015, 10:47:08 pm »
Hmm, I have some more suggestions.

14) The readings above suggest that the MS-2000 in the 400V range might be working?  Can you measure the large filter capacitor of a SMPS?  It should be around

220VAC x 1.41 = 310VDC.  It should be steady and stable.

15) The 400mV range might be working.  Can you test something in that range?

16) I think some of the readings could be due to leakage current.  A isopropyl alcohol (IPA) bath with a clean toothbrush scrubbing might be in order (both sides of the DMM pcb).   Let it dry thoroughly, overnight or use a fan, before reassembly.
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #21 on: October 21, 2015, 06:45:09 pm »
14. METEX have AC-DC adaptor 7.5VA, 1A. He has not use AC 220V directly.

15. Test with 300mV but nothing voltage is fluctuate.

I measure all pin on MAX134 with my oscilloscope and open probes.
Power on MAX134 is correct and stable.
With open probes have bad waveform on:
- pin 39 "FILTER RESISTOR IN"
- pin 42 "BUFFER 1"
- pin 21 "INTEGRATOR IN"
- pin 20 "INTERGATOR OUT"
Maybe my chip MAX134 is broken.  |O :'(
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #22 on: October 21, 2015, 08:31:03 pm »
14. METEX have AC-DC adaptor 7.5VA, 1A. He has not use AC 220V directly.
I think we have a lost in translation here.

I'm asking you to put the MS-2000 into DCV 400V range and use the MS-2000 to measure a device that has a SMPS, like a DVD player, and measure the large filter capacitor.  We want to know if the DCV 400V range on the MS-2000 is working correctly and giving stable readings.

Quote
Maybe my chip MAX134 is broken.  |O :'(
It is possible the MAX134 is bad, but I would give the pcb an IPA bath before coming to that conclusion.
 

Offline jstanchevTopic starter

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Re: Metex MS-2000.
« Reply #23 on: October 26, 2015, 08:47:39 am »
I washed the boards but the voltage is fluctuate again.
 

Offline retiredcaps

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Re: Metex MS-2000.
« Reply #24 on: October 26, 2015, 05:39:14 pm »
MAX134 replacements can be found on aliexpress starting at $14.16 USD + free s/h.
 


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