Author Topic: exceeded 10A unfused multimeter input (Read 13091 times)

cosminnci · « **on:** October 20, 2013, 02:08:52 pm »

I have an AXIOMET AX-MS8250 with an 10A unfused ampmeter, today I made an foam cutter tool and measured the amps true the 10A port

, it read 30 or so amps then turned it off.
now it measures 1.5v battery as 4.15v so something got damaged, the buzzer stays on when I go to continuity tester.
should I start looking for another meter? or is it still fixable?

regards,
Cosmin

KD0CAC John · « **Reply #1 on:** October 20, 2013, 02:14:12 pm »

Almost anything can be fixed , if not there should be some learning and you may even be able to mod

geo_leeman · « **Reply #2 on:** October 20, 2013, 02:18:23 pm »

I'd try to go for a bit more safe meter and maybe take a look inside this one. It sounds like it may be too cooked to fiddle with.

DL8RI · « **Reply #3 on:** October 20, 2013, 02:18:40 pm »

Hi,

I found this Multimeter at a store in the web, 25€. Throw it away.

cosminnci · « **Reply #4 on:** October 20, 2013, 02:57:31 pm »

I looked inside it didn`t see anything fried.
it did the job for what I needed it, I wanted a fluke but the prices are more than I`m willing to pay for a meter, maybe now I`ll have to consider one with fuses on the 10A port.

Bored@Work · « **Reply #5 on:** October 20, 2013, 04:09:25 pm »

Quote from: cosminnci on October 20, 2013, 02:57:31 pm

it did the job for what I needed it,

Apparently it didn't.

c4757p · « **Reply #6 on:** October 20, 2013, 04:14:23 pm »

Using a multimeter with an unfused 10A range is like going out in the winter wearing gloves but topless.

Lightages · « **Reply #7 on:** October 20, 2013, 04:50:27 pm »

I am sorry to hear of your problems Cosmin. This is a good example why people make so much noise about buying a quality meter. There is a saying; "Buy quality and cry once at the price. Buy cheap and cry many times."

So now you have a choice, try to fix it or buy another meter. Personally I would do both because you won't know if that meter is accurate anymore without a reference.

cosminnci · « **Reply #8 on:** October 20, 2013, 05:01:48 pm »

Luckily I see a fluke 177 or 179 at a good price at TME where I buy parts from, I think I will go for it. fixing the old one probably won`t get the precision, so I better get a new one.

regards,
Cosmin

Lightages · « **Reply #9 on:** October 20, 2013, 05:14:25 pm »

If you are considering one of those expensive Flukes, then consider either the Brymen BM525 or Brymen BM869. They are extremely well built and better bang for the buck than the Flukes. There is lots of information on them here, just search. The BM869 plus the PC data cable and software costs less than the Flukes.

Oh yes, whichever you buy, buy a set of extra fuses

zapta · « **Reply #10 on:** October 20, 2013, 05:41:56 pm »

Quote from: cosminnci on October 20, 2013, 05:01:48 pm

Luckily I see a fluke 177 or 179 at a good price at TME where I buy parts from, I think I will go for it. fixing the old one probably won`t get the precision, so I better get a new one.

regards,
Cosmin

If you can afford it, good for you. If not, there are very good DMMs for much less.

It's not about what test equipment you have but what you do with it.

cosminnci · « **Reply #11 on:** October 20, 2013, 05:50:10 pm »

It is a vital equipment for me, and I use it quite often but you know there is never the right time to need it and to afford it.
till now I already had 3 or 4 no-names, the last one was ok till this fuse thing

definitely I`ll buy extra fuses

geo_leeman · « **Reply #12 on:** October 20, 2013, 05:50:41 pm »

It's very important to have equipment you can trust. Low quality test kit can lead you on chases you don't want to go on... or worse can physically harm you!

ejeffrey · « **Reply #13 on:** October 20, 2013, 06:28:23 pm »

There are a huge range of products between el-cheapo piece of crap with an unfused amps range and a fluke. You can look at dave's multimeter shootouts or buy one of the other products recommended here and have a totally solid tool for between $50 and $150. For the average electronics hobbyist you will get a much more versatile tool than a fluke in the same price range. I would stay away from the fluke 170 series. They are great meters for what they do, but the resolution and range is pretty limited.

One more thing: if you want to measure high currents like yolur foam cutter, look for a clamp meter. Some of them are AC only, some can do DC as well.

Stonent · « **Reply #14 on:** October 20, 2013, 07:25:36 pm »

Quote from: c4757p on October 20, 2013, 04:14:23 pm

Using a multimeter with an unfused 10A range is like going out in the winter wearing gloves but topless.

A friend in HS from Connecticut said his had used to get up at 6:00AM shirtless, barefoot in nothing but a pair of boxers and shovel snow off the driveway and sidewalk every day in the winter.

He had 3 boys, so must be good to keep your parts cool.

retiredcaps · « **Reply #15 on:** October 20, 2013, 09:40:07 pm »

Quote from: cosminnci on October 20, 2013, 02:08:52 pm

or is it still fixable?

I couldn't find a manual for the AX-MS8250, but the Velleman DVM1500 looks identical and it has a manual.

http://www.velleman.eu/products/view/?country=nl&lang=en&id=373622

Looking at the specs of 3 updates/sec, 4,000 count, 15 min APO with buzzer sounding off after 14 min suggests it is using a FS9721 IC.

http://www.ic-fortune.com/upload/Download/FS9721_LP1-DS-19_EN.pdf

In Section 15.1, there is a common use circuitry that might give you clues on what to check?

Some questions.

1. What does a 9V battery measure?
2. If you short out the probes on resistance mode, what does it read?
3. If you measure a 1K ohm resistor, what does it read?
4. If you short out the probes on DCV mode, what does it read?

Jon86 · « **Reply #16 on:** October 20, 2013, 09:52:02 pm »

I've done this before with one of those $10 cheapies. Tried to do voltage with it in the 10A

Weirdly it just turned off within a fraction of a second, there was no obvious internal damage at all, but I never got anything out of it. At least it gave me the incentive to buy a half-decent VC99!

cosminnci · « **Reply #17 on:** October 21, 2013, 02:16:53 pm »

@retiredcaps it does ranging and measures 000.0mv
on ohms it does ranging continuously but it is steady on 000.0 ohm
shorting the probed does nothing, it behaves like it is a short inside.

regards,
Cosmin

retiredcaps · « **Reply #18 on:** October 21, 2013, 10:31:02 pm »

Can you post a picture of the pcb? It may help us figure out what is wrong. I might have a guess as to what is wrong depending on your picture.

Psi · « **Reply #19 on:** October 22, 2013, 10:01:44 am »

When this happened to me the fault turned out to be a failed small signal diode.

cosminnci · « **Reply #20 on:** October 22, 2013, 03:00:26 pm »

I looked over the pcb but did not noticed any burned part, I unsoldered the shunt for test.
attached is the foto of the pcb.

retiredcaps · « **Reply #21 on:** October 23, 2013, 07:19:52 am »

I will need a couple of days to suggest some tests. Right now, I have other things to deal with and can't spend a couple of hours doing one task right now.

cosminnci · « **Reply #22 on:** October 23, 2013, 05:36:04 pm »

ok,
thank you.

retiredcaps · « **Reply #23 on:** October 23, 2013, 11:11:36 pm »

Okay, I'm not an expert, but I'm keen to learn so some of my suggestions below may be wild goose chases.

The tests below are based on the 9721 datasheet. Since I don't have your multimeter in front of me, you will have to find the corresponding parts. Refer to section 15.1.A Common Use Circuitry (100 pin package IC) for the pinout diagram.

For example, R26 is a 10 Mohm resistor. The 10 Mohm resistor on your pcb may not be numbered R26, but but it will be the resistor that is connected to pin 26 of the IC.

I'm going to break this into two parts. The first will be measuring the volts/ohms jack and the second will be measuring the 10A jack. All measurements can be initially done "in circuit".

Volts/ohms jack
---------------

1) Measure the resitance of PTC (just above the 0.5A fuse). It should be around 1 kohm.

2) Measure the resistance of R26. This resistor is connected to pin 26 (TENM) of the IC.

3) Measure the resistance of R25. This resistor is connected to pin 24 (ONEM) of the IC.

4) Measure the resistance of R24. This resistor is connected to pin 22 (HUNK) of the IC.

5) Measure the resistance of R23. This resistor is connected to pin 20 (TENK) of the IC.

6) Measure the resistance of R22. This resistor is connected to pin 18 (ONEK) of the IC.

7) Measure the DCV of a 1.5V AA battery with the AX-MS8250. It should show 4.15V DC as you wrote earlier.

8 ) Get another multimeter (let's call it DMM-B) and set it to measure DCV.

9) Put DMM-B's black probe on the AX-MS8250 COM jack. Put DMM-B's red probe
on pin 26 of the IC.

10) Put DMM-B's black probe on the AX-MS8250 COM jack. Put DMM-B's red probe on pin 24 of the IC.

11) Put DMM-B's black probe on the AX-MS8250 COM jack. Put DMM-B's red probe on pin 22 of the IC.

10A jack
--------

12) Measure the resistance of R19. This resistor is connected to pin 13 (SMV) of the IC.

13) Measure the resistance of R31. This resistor is connected to pin 9 (SGND) of the IC.

14) There are four diode next to the 0.5A fuse. Measure each diode using the diode test function using DMM-B. You should have two readings for each diode.

Report your findings using the exact numbered sequence above so it is easy to read. For all resistors, report its color code or SMD markings so we can verify if they are correct.

PS. This thread regarding how Martin killed the UT90C is somewhat related because it uses the same 9721 IC and may be helpful?

http://mjlorton.com/forum/index.php?topic=24.0

cosminnci · « **Reply #24 on:** October 26, 2013, 03:51:56 pm »

thank you for helping me, I read Martin`s blog, interesting topic, seems very related to my first findings.

there is some progress for my merer, I started to check a few points on the list, but meanwhile I found other problems.
the fuse was blown, I placed a temporary one.
the PTC is 1.3 ohm instead of 1.
I kept stressing it and sometimes it starts.
I uploaded a little video of how it behaves.

it starts up only after a very short impulse? I unhook the power clip very shortly and it starts.
9.5v battery reads 25V
1.3v reads 3.5v
and when switching to the continuity test it does an pulsating sound.

I still have a few parts to check but I can`t explain why it starts measuring on a very short reset.

regards,
Cosmin


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Author Topic: exceeded 10A unfused multimeter input (Read 13091 times)

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