Gossen Metrawatt Metrahit 29S (M229A) Issues

[Trader]

I'm testing a Gossen 29S, after 3 days it exhausted 2 new alkaline batteries (1.62V each), I'm not sure if I turned it off, but I suppose it should turn off automatically.

[retiredcaps]

Reference.

https://www.gossenmetrawatt.com/resources/zz_tam/hit28-29s/db_gb.pdf

According to above, battery life for alkaline is roughly 100 hours and that "the device is switched off automatically if the measured value remains unchanged for a period of approximately 10 minutes, and if none of the controls are activated during this time. Automatic shutdown can be deactivated."

I would check to see if automatic shutdown is activated or not.  If the meter did not turn off automatically, then yes, I can see how the batteries go dead after 72 hours, if the rated battery life is roughly 100 hours.

As for using an external power supply, again from the pdf above

"Connector Jack for External Power Supply Our NA5/600 can be connected for long term measurement, especially in memory mode operation, and for power disturbance recording. As opposed to common plug-in power packs, the NA5/600 includes a regulated output with minimal residual ripple and coupling capacitance to the mains input, as well as a highly insulated power cable. Measurement accuracy influences are thus minimized, and there is no impairment of electrical safety."

[giosif]

Do you have a variable power supply and a way to measure current?
If yes, can you power the meter from the variable power supply (make sure to set the correct output voltage on the power supply) and measure how much current the meter draws in OFF state?
Normal current draw should be around 100 uA.

Coincidentally, I am troubleshooting a 26M which is drawing about 3 mA in OFF state, which will obviously drain the batteries very quickly.

[giosif]

If I find the culprit, I will share here.
I had a similar issue with a Tektronix TX1/TX3 or Fluke 183/185 (can't remember which one exactly, but it's somewhere here on the forum) and, after desoldering/resoldering quite a few components, I traced the issue to an SMD ceramic cap which was acting like a resistor.

For my 26M, I think I might have caused this, when accidentally applying about 30V to the battery terminals, instead of the expected 3V. 
Interestingly, the meter survived (so, probably, your 3.3V adapter shouldn't be an issue, but don't trust me on that), but something must have suffered during that time.

For the LEDs, I will look to test, but it might take a while until I re-assemble the unit.
In any case, multimeters being able to turn on some LEDs but not measuring the voltage drop is quite a common thing.
Only a few multimeters can provide the voltage (in diode mode) to be able to light up all types of LEDs (particularly the white and blue ones) and measure the voltage drop at the same time.
One such example is the venerable Fluke 87V.

[Trader]

@giosif, check this out: https://www.eevblog.com/forum/metrology/most-accurate-modern-handheld-dmm-just-curious/msg1134532/#msg1134532

Powered from my computer's USB port, the meter draws about 74mA (YZX studio monitor, courtesy Franky Tong).
2 AA batteries only last approximately an eye-watering 16 hours.

Which connector plug is that? The manual only says "NA5/600", I want to find a similar o eBay.

[WackyGerman]

Well I also have a Gossen Metrahit 29 S and I can tell you that yours has a strange behaviour so there must be an issue in the multimeter .
The batteries will last for sure longer than 3 days . I need to replace them every three month even it is turned off . The internal clock needs some power but this is not that much than yours does . That s normal and you can read it in the manual . Gossem Metrahit says that you should take out the battery if you do not use the multimeter for a longer time . My guess is that there must be a short circuit somewhere in the multimeter . In use it also drops the voltage down so that you cannot measure diodes properly

[giosif]

@giosif, check this out: https://www.eevblog.com/forum/metrology/most-accurate-modern-handheld-dmm-just-curious/msg1134532/#msg1134532

Powered from my computer's USB port, the meter draws about 74mA (YZX studio monitor, courtesy Franky Tong).
2 AA batteries only last approximately an eye-watering 16 hours.

Which connector plug is that? The manual only says "NA5/600", I want to find a similar o eBay.

I am not sure what you mean with that quote but, to be clear, I was referring to current draw when the meter is OFF, not when turned on.

For the connector plug, good luck finding that and, please, let us know if you find one that works with the meter.
All I was able to find on eBay was the actual power supply from Gossen but, whenever I see it, it goes for silly prices (same as the USB-IR adapter).

[Assafl]

I think it is a 3/32" regular 2-way phone plug. Needs to be regulated to the voltage written or the 29s doesn't work well. I think there are two voltages for two models of the 29s black dial or the old green dial one - the latter requiring an odd 4.2V supply and the former requiring 5V. Even though it seems 5V should work - it doesn't and you need to add a diode to drop the voltage....

The plug should have a rather narrow barrel or it won't fit in the recess. Also, my guess is that like Fluke, they'd use a transformer and cable that are isolated/insulated to match the Cat rating of the instrument. So use a plastic barrel to match....

The battery (when off) lasts for at least months. 

As for the measurement range for the LED - The output of my 29S is almost 3V hence the LEDs light up. But indeed it only measures to 1.8V. Not sure why. I have a technician GMC (called the 16I) which is good for repairing washing machines - that one also does 3V but measures up to 3V.

Indeed the only reference to the 1.8V limit is "by the way" in the manual. The spec sheets say 3V and ignores the 1.8V limit. I tried to find a reference as to whether this changed from the green to black dial instruments - but couldn't.

[coromonadalix]

The 29s will consume more power in auto mode, since it has to sense the input and do some function and or range changes if needed.

The diode specs test are 3v at 1 ma,  not every model of leds will work on the 29s, in some case(s)  i cant test some blue leds,  Thats why some meters have an higher voltage output,  i think the eevblog 121gw is perfect fo that.

Same goes for my fluke 189 and other meters at my job in the 83 and 87 series too.

For theses, i use an 20 ma limited psu with a 5v source thru a resistor ... i try to know the led(s) spec  for testing ??

[Trader]

Assafi, M229A (29S green version), and M229E (29S not green) are exactly the same, the specs in the manual are everything the same. The M229E received this number because is a Kit, comes with other accessories. The only "upgrade" is the Metrahit Energy.

External power supply NA4/500 was available up 2003, after that is NA5/600. The DMM accepts between 3.5 and 5V (average is 4.2V).

ps.: I liked more the colors from the green one, the symbols are a little bigger with better layout IMHO.

[giosif]

If I find the culprit, I will share here.
[...]
For my 26M, I think I might have caused this, when accidentally applying about 30V to the battery terminals, instead of the expected 3V. 
Interestingly, the meter survived (so, probably, your 3.3V adapter shouldn't be an issue, but don't trust me on that), but something must have suffered during that time.

Sometimes, it pays off to know how something broke: due to the above accident, I checked the circuit close to the battery connection and, sure enough, found a 5.6V Zener that wasn't 5.6V in reverse bias anymore, but more like 1.3V (which is well below the normal battery voltage of 3V) - see attached picture for the diode in question.
Replacing the component with a new 5.6V Zener dropped current consumption (again, in OFF state) down to about 600 uA.
Still a bit high to my liking, but major advance from the initial 3 mA.
Hope this helps...

[Assafl]

External power supply NA4/500 was available up 2003, after that is NA5/600. The DMM accepts between 3.5 and 5V (average is 4.2V).

ps.: I liked more the colors from the green one, the symbols are a little bigger with better layout IMHO.

Agree about the color.

I don't think 3.5-5V work. In fact - to make it work I had to add a diode. I don't remember the details (it may have been something like a bat symbol acting up) - I just remember that when I made my own adapter (using a 5V wall wart) I had to drop the voltage. Perhaps it isn't a showstopper to use it at 5V - I just remember it worked - but oddly so... I seem to remember odd measurements (but I may be mixing it up with another DMM)...

[Assafl]

The diode specs test are 3v at 1 ma,  not every model of leds will work on the 29s, in some case(s)  i cant test some blue leds, 

That is if you want to see the LED light up. If you want to measure the forward voltage drop of the LED - you can only measure up to 1.8V (even though the instrument will supply nearly 3V).

[Wytnucls]

I don't have the schematics for the 29S, but I would first check components of the battery reverse current protection module, if there is one.
Best of luck with the fault finding.

[giosif]

Yeah, looks to me you'll have to take the board out of the meter, which is always a pain with Gossen meters, since you need to desolder the connections to the input jacks (that's the part of the Gossen meters I like the least).
What I usually do, in order to avoid heating the metallic part of each input jack too much (and, thus, melting the plastic surrounding it) is to plug in a 4mm shrouded banana connector into the jack, before applying heat to the jack with the soldering iron and melting the solder.
Once the board is out, it would be good to take some pictures of the board itself (both sides, with the LCD removed) and post them here.

[coromonadalix]

If you ever desolder the input terminals,  be very careful and do it pretty fast, the plastic around the plug may or will melt very fast, i did have to get the board out of my 29s  and i saw the plastic was about to melt ...

I changed the battery holder and the battery clip

[ace_ventura]

Each input terminal have small hook on the solder side - you have to push the wire down when you desoldering it.

My 28s model (old one) consumes 9.1 - 14.6 mA depends to selected range; 112 uA when OFF. I bought it very cheap as non working. There was some kind of pollution under MAX856 (3.3/5V step-up converter) on the input - chip stucks in 3.3V mode and defective ICL7660 (negative booster). After cleaning and replacing ICL chip the fault is solved.

Testing LED's on my DMM reports same results.

28s and 29s shared same user manual, but there is a note about non-use periods for 29s model.