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Thread: Major Tech MTD70T

  1. #11
    Diamond Member AndyD's Avatar
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    Okay so with no more ado lets void the warranty and see what it has to offer.

    The case is a typical clamshell type with 4 screws holding it together. This particular specimen had only 3 screws holding anything, one of them was completely stripped. The screws are self tapping and the posts they screw into have no threaded insert, this is a typical issue with cheap testers.

    Separating the clamshell case revealed a very nice deep overlapping flange all the way around the bottom of the case. The overlap is 7 or 8 mm which is important because if anything goes wrong whilst the tester is in use this overlapping flange will contain any arc flash and ensure that your fingerprints remain on your fingers. The only problem here is that they made a relatively large hole for the lanyard to go into which kinda defeats the object entirely.

    It appears to be plain PVC, if you cut it there's no signs of any fibreglass reinforcing mixed in with it and there's no recycling number or plastic ID numbers. It's also a one-time moulding, there's no rubberised overmouldings on the corners or anywhere else.


    Click image for larger version. 

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  2. #12
    Diamond Member AndyD's Avatar
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    It's a single PCB, single chip design. The sockets for the leads are made from pieces of bent steel soldered direct onto the board.

    There's a sounder, 3 LED's, a few resistors, a few caps and a single PTC device, there's really not much else to it.....which is where the problems start.

    Click image for larger version. 

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    On the input side there's no HRC fuses, no MOV surge protection, no diode bridge and no separation slots in the PCB. The four 2.5meg resistors that give 10meg input impedance are very small SMD devices which will discintigrate in a cloud of smoke if there's ever a transient voltage. The only safety protection offered is a poorly soldered PTC which might work for normal overvoltage but it's far too slow to to give protection in the case of transients. Also there's no flashguard panels moulded into the case around the input components. Finally, I didn't have the patience to get my vernier out of my workshop but I have grave doubts about the separation distance between the two solder terminals on the battery compartment and the pieces of bent steel they pass off as sockets for the leads when the two halves of the case are assembled.

    Click image for larger version. 

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ID:	7985

    On close inspection the track on the PCB between the red lead socket and the first 2504 resistor is thinner than the other tracks in the input area. It's not indicated as such but I wondered if it was designed for this track to blow open circuit if there was ever a transient event. Either way I think their CATIII 600V rating is highly questionable, I wouldn't recommend using this tester beyond a recommended CATII application on lower current rated final circuits and on appliances. I wouldn't personally use it for anything beyond DIY use. Never in a million years would I use it on a 3-phase DB and I'd be wearing my electrical PPE gloves that cost 5 or 6 times the price of this tester if I was using it on a single phase DB.
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  3. #13
    Diamond Member AndyD's Avatar
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    I was originally intending to do a more in depth review including setting up a square wave supply and checking out its true RMS capabilities but to be honest depression set in and I kinda lost interest after seeing the input circuitry or lack thereof because regardless of how accurate or capable it is with testing it's still useless as a piece of equipment for any professional sparky because of it's lack of protection for the user.

    Here's a picture of the top side of the clamshell case with a better view of the stripped screw holes and the garbage selactor switch contacts.

    Attachment 7986

    And here's a picture of the back side of the PCB.

    Attachment 7987
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  4. #14
    Diamond Member AndyD's Avatar
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    Having lost interest in the tester I turned my attention to the leads. Ever the optimist I saw a glimmer of hope...a distant silver lining nogal that I might still end up with a nice zip pouch and a halfway decent set of test leads and a couple of usable AA batteries in return for my 450 hard earned Rands.

    Plugging the leads into the tester and shorting them out whilst selecting the continuity function gave a fluctuating reading of 0.4 - 0.5 ohms. Alas this wasn't what I was hoping for. I tested the resistance of the red lead using a Fluke multimeter and it was 0.27 ohms and the black lead measured 0.24 ohms. For leads that are supposedly rated at 10Amps I'd expect to see maybe 0.1 ohms per lead maximum.

    Cutting the red lead revealed the issue which was just good old fashioned lack of copper and after fully dissecting the rest of it I could see that the solder joint onto the top of the probe was also a bit dry.

    Attachment 7988
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