Digital Multimeter will not record resistance

[davg]

My 52-0060-2 Mastercraft Digital Multimeter will not record Resistance. I accidentally but the two leads across 120 vac while it was set to the Resistance scale.
When set to 2000k ohm it shows all zeros, 200k it shows 00.7 and strike the two leads together it will show 00.0, 20k it shows 0.71 and strike the two leads will show 0.00, 2000 scale shows 722 and goes to 000 when the two leads touch. 200 scale reads 78.3 and drops to 00.3 when the two leads touch. The diode scale reads 297 and drops to 000 when the two leads touch.
All other scales seem to be working OK.
Anyone care to diagnose the possible problem this accident may have caused? and why I would be getting these readings on the Resistance scale?

[budm]

Re: Digital Multimeter will not record resistance

Did you open it up and see any burnt component inside yet?

[davg]

Re: Digital Multimeter will not record resistance

Thanks budm. Yes I opened it up but didn't see anything obvious. I haven't done any testing yet have to get another meter.

[tom66]

Re: Digital Multimeter will not record resistance

You most likely burnt some part of the divider or current source for the DMM. Lots of precision resistors - it would be tricky to repair.

[gilly1984]

Re: Digital Multimeter will not record resistance

I left mine on diode check and give it 240v. giving me mad readings on every setting so I punched it and threw it in the bin.

[tom66]

Re: Digital Multimeter will not record resistance

My £20 and £100 meters have both survived 230V on ohms and diode test.

My BK 2709B made up some random number, on eevblog video it just switched off.

My £20 meter just showed OL and was still accurate.

[gilly1984]

Re: Digital Multimeter will not record resistance

the 2 I have blown are £4.

just scouting eBay now for a slightly better one but I'm guessing most of the cheaper ones are the same internals, just with a different housing on.

[retiredcaps]

Re: Digital Multimeter will not record resistance

My 52-0060-2 Mastercraft Digital Multimeter will not record Resistance.

1) If you want the exact same one, it usually goes on sale for $10 in this kit at Canadian Tire.

http://www.canadiantire.ca/AST/brows....jsp?locale=en

2) I have used an earlier version of this Canadian Tire multimeter

http://www.canadiantire.ca/AST/brows....jsp?locale=en

and it seemed okay. It goes on sale for as low as $19.99 or $14.99 if you are patient.

I borrowed the above from a friend so I was obviously not going to see if the ohms range would survive on mains.

3) Better multimeters are designed to survive "oops" moments and as tom66 mentioned Dave Jones at eevblog regularly does the ohms/mains test in all his reviews.

4) Martin Lorton over at

http://www.youtube.com/user/mjlorton/videos

killed his Uni-T 90C trying to measure frequency and turn the rotary dial past ohms while the probes were plugged into 220V AC. Details in this video

http://www.youtube.com/watch?v=PJQeI...CD696&index=23

5) If you want to spend a bit more, there are a number of other options.

[davg]

Re: Digital Multimeter will not record resistance

So guys not worth the effort? Your right, with the exception of a diode an a couple resistors and 2 capacitors the components are rather small inside there.

[retiredcaps]

Re: Digital Multimeter will not record resistance

So guys not worth the effort? Your right, with the exception of a diode an a couple resistors and 2 capacitors the components are rather small inside there.

Post a good focused picture so we can see.

[modemhead]

Re: Digital Multimeter will not record resistance

From the picture retiredcaps posted, the meter looks like a re-packaged "830" style meter. In which case, yes, it's hardly worth the time. Anyway, the schematics that I have seen for those type meters show a PTC (thermistor) and a transistor wired as an zener diode (collector/base shorted) is switched in to protect the ohms, continuity and diode-test ranges from over-voltage. Since your meter reads near zero, I would hazard a guess that the transistor has become a near-short. If that's right, simply removing it might restore functionality, although leaving the meter with no protection at all.

[davg]

Re: Digital Multimeter will not record resistance

Post a good focused picture so we can see.

As requested

[davg]

Re: Digital Multimeter will not record resistance

From the picture retiredcaps posted, the meter looks like a re-packaged "830" style meter. In which case, yes, it's hardly worth the time. Anyway, the schematics that I have seen for those type meters show a PTC (thermistor) and a transistor wired as an zener diode (collector/base shorted) is switched in to protect the ohms, continuity and diode-test ranges from over-voltage. Since your meter reads near zero, I would hazard a guess that the transistor has become a near-short. If that's right, simply removing it might restore functionality, although leaving the meter with no protection at all.

Thanks modemhead can you identify that PTC arrangement on the pictures I have attached? And if I can remove this why would I not be able to replace it? I assume it consist of a number of small components?

It is not the cost that motivates me its the need to keep these things out of the landfill???

[Kiriakos GR]

Re: Digital Multimeter will not record resistance

I like to keep things out of the landfill too.
And so you have the option to use it exclusively as DC voltmeter.

There is also multimeter at the low cost segment which they do have over voltage protection in all ranges.

Yes the over voltage protection is about protecting the meter it self.
The CAT category protection is about the user.

I believe that it is time to advance by getting an properly made multimeter.

[budm]

Re: Digital Multimeter will not record resistance

R9 (4700) looks discolor compared to other resistor. Look real close at all the resistors to see any blister on the body.

[davg]

Re: Digital Multimeter will not record resistance

R9 (4700) looks discolor compared to other resistor. Look real close at all the resistors to see any blister on the body.

Thanks budm R9 seems to be a different resistor it has a # sp MZS on it. Is this the one you are referring to?

[modemhead]

Re: Digital Multimeter will not record resistance

Disclaimer here: All these type meters have a similar heritage and similar circuitry, but I'm looking at a schematic for one that doesn't match yours exactly. So it's all stabs in the dark and wild guesses.

R9 (big orange blob) is the PTC thermistor. Q3 looks like it is the transistor I referred to in my previous post, because it seems to only have two traces leading to it, and it would have its base and collector tied together. It's function would be to conduct and cause the thermistor to temporarily open up during an overload on the Ohms range. I guessed that it was shorted. So Q3 is the component you could remove and check that theory, if you are handy with the soldering iron.

I could not in good conscience recommend spending any money to fix this meter because it is essentially disposable. So for once I might agree with the mad Greek electrician that it's time for a better one.

[budm]

Re: Digital Multimeter will not record resistance

Sorry, not the R9, the resistor under the black wire that I cannot read the desigator, R7A???. R9 designator is for the empty pads

[davg]

Re: Digital Multimeter will not record resistance

Thanks modemhead I may give it a try I have nothing to lose since the thing is disposable. I have purchased the a new meter the Mastercraft 52-0052-2 just because its readily available. It serves the purpose.

[retiredcaps]

Re: Digital Multimeter will not record resistance

FYI. Canadian Tire has selected multimeters for 75% off MSRP from Oct 25 to Oct 31 (as I alluded to in post #8). Your 52-0052-2 is not listed as 75% off, but the manual range almost equivalent is on sale for $13.69.

http://www.canadiantire.ca/AST/brows....jsp?locale=en

My thursday flyers get delivered a day or two late so that is why I didn't post this info on thursday night.