Tenma 72-6000 multimeter teardown

[GnatGoSplat]

This is the multimeter I've been using for the past 14-years.  Battery is getting low, so I used that as an opportunity to disassemble and take pics.
I'm curious if this looks like cheap crap or no?  Even if not very good, it's served me well and I love the REC function that displays min and max in the sub displays.  I bought it new from MCM Electronics in 1998 I think, for around $80.  What initially attracted me to it were the features for the price.

For the last 5-years or so, it had a problem where in Ohms mode, shorting the leads together would show abnormally high values.  Usually around 1-10 ohms.  I would need to rotate the knob back and forth a few times to get lead resistance below 1 ohm.  Recently, the problem worsened and it wasn't unusual for lead resistance to measure 20-30 ohms.   That prompted me to pull the knob off the PCB and clean the wipers and gold contacts with an eraser.  That seemed to do the trick and leads shorted now show 0.2-0.3 ohms so it's good as new now.  I do wish there was an affordable multimeter where all functions are controlled by soft-buttons so I don't have to worry about this problem in the future.



No components on the back of the main PCB.


PCB assembly is not physically attached to the housing with any fasteners.


Consists of 2 PCBs attached by a header.  One adjustment on this side.


3 trimpots for adjustment placed together.


Remove 4 screws and the PCBs separate easily.  Looks like main DMM/ADC chip is a MAX134 connected to some MCU which must be common enough that they felt the need to sand off the p/n.  Looks much more sparse inside than the high-end DMM teardowns I've seen here!


Silkscreened on the main PCB says "SEIN ELECTRONICS PMM208".  The company is based in South Korea.  I guess 14yrs ago was before the proliferation of Chinese brands.

[T4P]

Stuff from korea is just slightly better than china anyway, if it's not LG
Stuff from Samsung are just some cheap china made crap now anyway (TV's still come from malaysia)


There ya go,
http://www.aliexpress.com/product-fm/526582916-Free-shipping-original-VICTOR-70C-3-5-6-Key-Touch-Digital-Multimeter-with-PC-interface-VC30278-wholesalers.html

[GnatGoSplat]

There ya go,
http://www.aliexpress.com/product-fm/526582916-Free-shipping-original-VICTOR-70C-3-5-6-Key-Touch-Digital-Multimeter-with-PC-interface-VC30278-wholesalers.html

Thanks, I do like the soft buttons on that.  It would actually be convenient not to have to turn the knob all the way through every single function just to get to capacitance, for example.  I would miss min/max recording on those sub-displays though.  I searched to see if that company had a higher model with sub-displays and min/max recording.  I found the 70F model looked like it had sub-displays, but when I took a closer look, I saw they are a clock and calendar.  Interesting, I've never seen a clock/calendar on a multimeter and never would have imagined wanting that feature, but there it is!

[T4P]

There ya go,
http://www.aliexpress.com/product-fm/526582916-Free-shipping-original-VICTOR-70C-3-5-6-Key-Touch-Digital-Multimeter-with-PC-interface-VC30278-wholesalers.html

Thanks, I do like the soft buttons on that.  It would actually be convenient not to have to turn the knob all the way through every single function just to get to capacitance, for example.  I would miss min/max recording on those sub-displays though.  I searched to see if that company had a higher model with sub-displays and min/max recording.  I found the 70F model looked like it had sub-displays, but when I took a closer look, I saw they are a clock and calendar.  Interesting, I've never seen a clock/calendar on a multimeter and never would have imagined wanting that feature, but there it is!

Where? O.o i don't see any on the victor website

[GnatGoSplat]

Where? O.o i don't see any on the victor website

Here it is:
http://www.aliexpress.com/product-fm/545503041-Digital-Multimeter-VICTOR-70F-Autoranging-wholesalers.html
Clock/calendar has gotta be a first on any multimeter I've seen!

[PA0PBZ]

Clock/calendar has gotta be a first on any multimeter I've seen!

What, no alarm? 

[sotos]

Clock/calendar has gotta be a first on any multimeter I've seen!

What, no alarm? 

Yeah it’s useful, it shows when you need to pack up and go home. 

[beltal]

  Alarm? haha, I cannot image what would happen if it rings when your boss beside you.  If you want to buy,  you can go here to see:
http://www.beltal.com/dhgexpress?uri=/product-fm/526582916-Free-shipping-original-VICTOR-70C-3-5-6-Key-Touch-Digital-Multimeter-with-PC-interface-VC30278-wholesalers.html
hope it can help you

[StubbornGreek]

I like how they implemented the banana jacks but the placement/protection of the fuses is balls.

[rsjsouza]

What is the COMM jack on the lower right side of the front panel? RS-232?

Pretty cool the ladder of vias in the scratched microcontroller PCB...

I would love to have a button-only DMM as well, but with the infamous "rotate and click" HP calculator keys... I lost count of how many times I pressed the damn rubbery button on various equipments but the function did not execute.

Well, maybe they don't exist, as a small DMM on its stand could quickly fall to one side when pressing the button... I'll keep dreaming...

[ivan747]

Why the hell do they have the frequency measurement function after the current measurement function!? It only takes a mistake to blow the fuse when measuring a simple circuit! Also, you would have to disconnect the meter before switching to the dedicated frequency measurement, come on!

[Monkeh]

Why the hell do they have the frequency measurement function after the current measurement function!? It only takes a mistake to blow the fuse when measuring a simple circuit! Also, you would have to disconnect the meter before switching to the dedicated frequency measurement, come on!

.. switching it through the current range won't do anything unless you have a probe in one of the current terminals.

[GnatGoSplat]

What is the COMM jack on the lower right side of the front panel? RS-232?

Pretty cool the ladder of vias in the scratched microcontroller PCB...

I would love to have a button-only DMM as well, but with the infamous "rotate and click" HP calculator keys... I lost count of how many times I pressed the damn rubbery button on various equipments but the function did not execute.

Well, maybe they don't exist, as a small DMM on its stand could quickly fall to one side when pressing the button... I'll keep dreaming...

Yep, the COMM jack is RS-232.  I remember trying it when I first go the meter because it seemed like an interesting feature, but I never really used it since.  I'm sure I still have the software for it on a floppy disk somewhere.

I'd never heard of the rotate and click HP calculator keys, had to look that up.  Interesting, now I'm curious how that works and how it feels.  I had an HP48G in high school and college which had a nice tactile feedback, but it predated rotate and click.

[rsjsouza]

I'd never heard of the rotate and click HP calculator keys, had to look that up.  Interesting, now I'm curious how that works and how it feels.  I had an HP48G in high school and college which had a nice tactile feedback, but it predated rotate and click.

You are right; I had the impression this type of keyboard was called "rotate and click", but this page proved me wrong. 

So scratch what I said before: I would love to have equipment with the older HP tactile feel (although I did not yet try the new so-called "rotate and click"). I think these older keyboards started with the old HP41 design.

My dad has a TI-59 that also has a great keyboard, but that was before they moved to the rubbery stuff.

[reliant_turbo]

What is the COMM jack on the lower right side of the front panel? RS-232?

Yep, the COMM jack is RS-232.  I remember trying it when I first go the meter because it seemed like an interesting feature, but I never really used it since.  I'm sure I still have the software for it on a floppy disk somewhere.

Hello,

i know this thread is old but i was hoping that you still have this meter/cable/software as i have the same meter (well sort of... ill explain below) and would like to log something over a long period of time to a laptop. I dont have the software nor the com port pinout. I reached out to MCM electronics years ago but they said they didnt have any info for me as it wasnt a current model. i figured id try again and my search led me here.

now my meter is a 72-6000 and has all the same buttons but my buttons below the screen arent all labeled and use on screen prompts to tell you what the function is. the model and such are printed in a different location too.

also, my circuit boards are different too.

Brian

[GnatGoSplat]

The software I can help with.  This is the original software.
https://drive.google.com/file/d/0B2dlXEQUB9tiRldCSUo0X1ozdzQ/view?usp=sharing

I can kind of help on the pinouts of the cable.  I can't find my cable, but I did find an old photo I took of the inside of it.

It's a 1/8" mono mini jack.  All I can really tell is RxD to the tip (white wire), DTR to the ring (red wire), and RTS connected to RxD via a resistor whose value I can't make out in the terrible pic.  Shield ground appears not to be used.

I'd be interested to see photos of yours.  Sounds like yours may be a newer version.

[reliant_turbo]

The software I can help with.  This is the original software.
https://drive.google.com/file/d/0B2dlXEQUB9tiRldCSUo0X1ozdzQ/view?usp=sharing

I can kind of help on the pinouts of the cable.  I can't find my cable, but I did find an old photo I took of the inside of it.

It's a 1/8" stereo mini jack.  All I can really tell is RxD to the left channel (white wire), DTR to the right channel (red wire), and RTS connected to RxD via a resistor whose value I can't make out in the terrible pic.  Shield ground appears not to be used.

I'd be interested to see photos of yours.  Sounds like yours may be a newer version.

thanks for the software.

bummer on the cable.

if you ever find it, let me know.

ill try to take some pics inside the meter soon.

Brian