EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: jstanchev on October 13, 2015, 10:45:59 am
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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.
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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?
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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/ (http://postimg.org/gallery/3cdgrg2lw/)
6. Yes it's work.
Connect red probe to scope plug W/F and see follow pictures:
(http://s21.postimg.org/ekq5nsqtj/DSCN3700.jpg)
Short probe and i see follow picture: (http://s21.postimg.org/5lqwja75z/DSCN3701.jpg)
Disconnect red probe from W/F and see follow picture: (http://s21.postimg.org/ofcpga5dz/DSCN3702.jpg)
This isn't problem for scope, work correct.
Greetings.
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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?
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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 (http://www.produktinfo.conrad.com/datenblaetter/125000-149999/126560-sp-01-en-DG_SCOPE_20MHZ.pdf)
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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.
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.
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 (http://www.produktinfo.conrad.com/datenblaetter/125000-149999/126560-sp-01-en-DG_SCOPE_20MHZ.pdf)
I will download and look later.
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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.
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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.
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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?
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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?
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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.
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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.
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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?
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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.
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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.
Fraser
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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.
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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.
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.
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.
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?
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.
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Are the above measurements the spark gap solder pads?
I am not solder spark gaps yet.
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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,
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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
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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.
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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 :'(
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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.
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.
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I washed the boards but the voltage is fluctuate again.
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MAX134 replacements can be found on aliexpress starting at $14.16 USD + free s/h.
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I found 2 type of MAX134CMH
1. MAX134CMH+D
2. MAX134CMH+TD
Which is difference?
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I found 2 type of MAX134CMH
1. MAX134CMH+D
2. MAX134CMH+TD
Which is difference?
Packaging? See mouser and digikey screenshots.
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I have a complete MS-2000 if you would like to buy a spare parts donor. It has a dead DC-DC converter and I just have not got around to repairing it. If you are interested, let me know what it is worth to you.
Fraser
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Who DC-DC converter doesn't work on Your METEX?
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I'll fix it and let you know ! 😆
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Today replace MAX134CMH.
Result is the same. |O |O |O :-//
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Today replace MAX134CMH.
Result is the same. |O |O |O :-//
The only thing I can think of is that there is still some contamination somewhere on the pcb.
In this recent Fluke 83 post, it wasn't very obvious at first glance there was a problem ...
https://www.eevblog.com/forum/repair/fluke-83-multimeter-repair-attempt/ (https://www.eevblog.com/forum/repair/fluke-83-multimeter-repair-attempt/)
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Hi all,
I found this thread because I had the same issue with my multimeter, mine is a Tenma 72-6640, another re-labelled Metex MS-2000.
I followed all the suggestions given, but I also had a blown resistor, the 1Kohm resistor labelled R221 in the DG Scope schematic and R52 on the DMM PCB, thanks to jstanchev for confirming me its value. I reaaly have no idea how I blew that resistor, but it helped me in finding the solution.
Thanks to the schematic I traced the signal path in the input stage and I found the protection transistors not shorted, but somehow damaged, they are Q59, Q60, Q61 and Q62 in the schematic, Q17, Q18, Q19 and Q20 on the PCB. To test the possible solution, I removed Q17 and Q19, in testing the DMM I had to be careful because there was no protection against either to over voltages (especially in the 400mV range), or to DC/AC voltages while measuring resistances. I did not use the auto range feature to be sure not to damage the MAX134.
The schematic diagram lists two possible types for these transistors, in my case they are KTC3875S Y-RTK. I replaced all four of them and of course the blown 1K resistor.
After replacement I cleaned with the ultrasonic cleaner both PCBs (not the one with the keyboard and the one with the display) with a 30 minutes bath in IPA at 50°C, then I "baked" the PCBs in the oven at 50°C for 10 minutes to let the alcohol evaporate completely.
Now everything works perfectly, input impedances are in specification, about 10MOhm in all ranges. I also measured resistors, capacitors (down to 115pF), DC and AC voltages, I tested also the frequency meter. Great!
I considered also the contamination issue. This may be possible because of the semi-sealed design of the DMM case and because of the rechargeable NiMh batteries inside. My issue started when the battery pack began losing its capacity, probably some exhalations from it caused loss of insulation between the traces and/or the components, considering also that I work with vacuum tubes and high voltages, this combination might have caused the resistor to burn and the subsequent damage to one ore more protection transistors. Anyway, now it is fixed but I will not use the autoranging feature for measuring high AC or DC voltages, the switch between 400mV and the higher ranges is done by a relais that might not be sufficiently fast.
Now I'm trying to restore the rechargeable battery pack, unfortunately I lost the old one after moving to the new house, if someone can post pictures of it and its schematic it would be very helpful. I do not remember if it has 2 wires (in this case no problem, one is the positive, the other one is the negative pole), or if they are 4 and this would be an issue, what are the other 2 for??? |O
Thank you all for the suggestions.
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Hello colleagues! Please share a circuit diagram for Metex MS-2000 or its equivalent Tenma 72-6640
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Hello yuraol, I did bot find any schematic of this meter, in this thread you can find the METEX DG SCOPE 20Mhz schematic whose DMM part is the same as the MS2000.
http://www.produktinfo.conrad.com/datenblaetter/125000-149999/126560-sp-01-en-DG_SCOPE_20MHZ.pdf (http://www.produktinfo.conrad.com/datenblaetter/125000-149999/126560-sp-01-en-DG_SCOPE_20MHZ.pdf)
If anyone can post the complete MS2000 schematic it would be helpful considering that MS2000 PCB labels are, of course, not the same as the DG SCOPE ones.
Thank you
Stefano