Harbor freight Cen-tech 90899 small teardown

[rsjsouza]

I just found lost somewhere a brand-new Cen-tech 90899 DMM and decided to open it up and see if anything interesting popped up. Well, I decided to take some pictures that evidenced the unfortunately but expected terrible assembly and design.

Interesting: I just saw PedroDaGr8's review of another Cen-tech precious piece of equipment...

Sorry for the low quality of the pictures; I was testing a new portable camera (also found in the same somewhere place as the DMM)...

Frontal view. Typical Mastech el-cheapo DMM, but with an ON/OFF switch. It says CAT II but does not have any indication of fused/unfused inputs.


Back cover. Several paper label warnings slapped to the back, probably to appease any lawyers...


Back cover, inside view. The spring is not only loose from the PCB, but the aluminum stick is peeling. Putting the cover back without shorting everything will be interesting...


Full inside view. Typical board for cheap DMMs, with average soldering and the unfortunately way too narrow clearances...


Input circuitry. Also typical narrow clearances, but the novelty is the slanted fuse...


Rest of the board. Also typical of cheap DMMs, although I haven't seen them that small yet


10 ohm resistor


Comparing with a Fluke 179


7k5 ohm resistor


Comparing with a Fluke 179


Voltage test (12V sealed battery)


Ampères test (12V sealed battery with 10 ohm resistor across)


Miliampères test (12V sealed battery with 7k5 ohm resistor across)


In summary: do never put this DMM across the mains leads... It may be a shocking or explosive experience... It is fine for small electronics circuits, provided the loose spring is not shorting anything inside...

[AlphZeta]

I bought one of these last year from Harbor freight when it was on sale for $5. It seems that this meter is just a rebranded DT-830 as everything looks identical.

But hey the price, it is OK if you just want to use it to check your batteries and trouble shoot some connectivity issues.

[rsjsouza]

AlphZeta, that is exactly the work I will put this DMM to do... My biggest surprise is the handy ON/OFF button, which helps when doing subsequent measurements (it also saves battery lifetime and the crank selector switch).

I'll just have to shut my eyes when opening the case to replace the battery, so I won't be hit with a flying spring...

[AlphZeta]

In summary: do never put this DMM across the mains leads... It may be a shocking or explosive experience...

And I forgot to add, these meters have been around for at least 15 years if not more, and they are surprisingly resilient to rough treatment. I recall back in 2000, a friend of mine accidentally stuck the leads in the mains to measure voltage but forgot that the range was set to mA. I heard a big bang and heard a loud curse. To our surprise, besides a blown fuse and somewhat melted tips of the test leads, the meter actually survived!!! And best of all, everything still works after we replaced the fuse.

Now, that may be the exception so don't try this at home.

[rsjsouza]

That is very interesting. Before I bought the Fluke 179, I had (and still have) an almost identical DMM (Steren 602-110) that was put to high voltages for quite some time and it worked well (check it here in action). However, I can tell the Steren is better built and has better clearances across the input terminals...

As you said, "past performance does not guarantee future results"...

[IanB]

Those little Cen-Tech meters can be adjusted to improve their accuracy using the trim pot inside.

Unfortunately they have a major failing: if you leave them unused for a while the contacts oxidize on the rotary selector switch and they give faulty readings. It's fixable by rotating the switch vigorously a few times to clean the contacts, but if you are not paying attention you will get a completely bad reading.

[robrenz]

Also only 1meg input impedance 

[rsjsouza]

if you leave them unused for a while the contacts oxidize on the rotary selector switch and they give faulty readings.

That's exactly what I was getting when I unpacked this DMM... Since I found it sitting in a box for "don't know how long" and even the low-bat indicator was on right from the start, that is probably the reason.

Also only 1meg input impedance 

Bummer... Oh well, that is what you get when you "buy" a free DMM... 

[T4P]

In my head they are better and cheaper versions of those crappy panel meters you can find for about the same price 
That said, they are good for being a panel meter voltage and current wise 

[amyk]

An "830" has sort of become a Chinese generic name for a cheap DMM (just like a 936, 937, etc. is not only a Hakko iron anymore, and an "858" is a hot air rework station.)

The separate power switch is odd, but maybe they added that with the savings from having the input PCB be cut out of the main one (notice the matching indentation on one side).

[(In)Sanity]

I appear to have a tendency to bring up some old posts.  Not exactly what I was setting out to do. 

I just purchased one of these from Harbor Freight for $2.00 on sale.   I had one goal in mind when I did so,  see how accurate a $2 meter could be.   Shockingly using my 3457A as a reference this little meter was an average of 0.25% on DC and about 0.5% average on AC.   The ohms ranges came in around 0.35% average and the ma ranges were again around the 0.25% average.  The only range that was out far was the 10 amp current range scoring in at 3% which is just in spec based on the paperwork. 

So I adjusted the trim pot to improve the DC accuracy and then using my 3457A as a reference I was actually able to get the 10 amp current range within 0.25% (or better).  How?,  by scraping a razor blade along the shunt wire until the reading came up to my reference meter.   Removing a tiny bit of material each time. 

So if your high current reading is to low one option is to shave the shunt.   Sounds a bit weird now that I write it out.   If it's to high you could push it down a little bit in the solder connection to in a sense shorten it or just cut it remove a tiny tiny amount and solder it back together again..shave as needed.  Has anyone else shaved the shunt before ?

Ohh and as a side note for anyone playing with one of these toys...don't use the supplied leads for anything much over 3 amps.   They will light up like a fuse at 10 amps.   5 amps they just get kinda hot.   Then again yours may be less crappy then the ones I got.   Just use caution.

Jeff

[retiredcaps]

Has anyone else shaved the shunt before ?

.  Best line of the year so far.

Well, it looks like they nick and shave $250 USD multimeters.

https://www.eevblog.com/forum/reviews/teardown-extech-ex570-my-first-but-also-last-extech/

[saturation]

See this too.

https://www.eevblog.com/forum/chat/kelvin-50le-multimeter-review/msg170027/#msg170027

I'd interested to see how the accuracy changes with ambient conditions.  What would happen if you used that Centech outdoors in winter, or summer?  Leave in a refrigerator for 1 hour to get in down to 40^oF and recheck any of its ranges.

[(In)Sanity]

See this too.

https://www.eevblog.com/forum/chat/kelvin-50le-multimeter-review/msg170027/#msg170027

I'd interested to see how the accuracy changes with ambient conditions.  What would happen if you used that Centech outdoors in winter, or summer?  Leave in a refrigerator for 1 hour to get in down to 40^oF and recheck any of its ranges.

I would love to do something like that.   I've actually been playing around with a peltier system which I could build in to a mini environmental chamber,   or I could just set the freezer to -25C and toss the meter in for a while.   Hmm,   I think I'll try the easy part first and just heat it a bit.   Hot air rework on 100C pointed in it's general direction should help warm it up.   Not very accurate,  but might show a trend.   

[Stonent]

Those little Cen-Tech meters can be adjusted to improve their accuracy using the trim pot inside.

Unfortunately they have a major failing: if you leave them unused for a while the contacts oxidize on the rotary selector switch and they give faulty readings. It's fixable by rotating the switch vigorously a few times to clean the contacts, but if you are not paying attention you will get a completely bad reading.

I have one of these I bought to troubleshoot a problem as my meter had gotten lost. There were two very similar looking models at the same price... I think I have the other. The accuracy seemed way off on everything I tested.  I played with the trim pot but it seemed to do nothing at all.

Holding the leads together seems to just cause it to wander around from 2 to 6 ohms randomly.

[(In)Sanity]

Those little Cen-Tech meters can be adjusted to improve their accuracy using the trim pot inside.

Unfortunately they have a major failing: if you leave them unused for a while the contacts oxidize on the rotary selector switch and they give faulty readings. It's fixable by rotating the switch vigorously a few times to clean the contacts, but if you are not paying attention you will get a completely bad reading.

I have one of these I bought to troubleshoot a problem as my meter had gotten lost. There were two very similar looking models at the same price... I think I have the other. The accuracy seemed way off on everything I tested.  I played with the trim pot but it seemed to do nothing at all.

Holding the leads together seems to just cause it to wander around from 2 to 6 ohms randomly.

Sounds like you just had a defective device.   They are built to such low quality it just amazes me how accurate they really are.  I was expecting them to be out by many percent,  not tenth's of a percent.   

Jeff

[SeanB]

Testament to just how robust dual slope integrating meters are, along with how good the 7106 design is, even many years later.

[(In)Sanity]

I just did a quick for fun test on this little guy.   It had been sitting all night in my basement lab at around 68F,  I used my hot air rework to slowly bring the thing up to around 90F and it only increased the least significant digit by 1.  That's a 0.1% increase.  Still not bad for a $2 meter.   I may do a more comprehensive test in the future instead of the quick and dirty test.

Jeff

[Stonent]

FYI: These meters are on through the end of today (Sunday 1/13/13) for $2.00

As always they have 2 different model numbers that look alike.

http://www.harborfreight.com/7-function-multimeter-98025.html

http://www.harborfreight.com/7-function-digital-multimeter-69096.html

I'm tempted to either buy the same one, and put the old one in the box (had it for a few months) and return it or buy the second one that I don't have and keep it.

[(In)Sanity]

FYI: These meters are on through the end of today (Sunday 1/13/13) for $2.00

As always they have 2 different model numbers that look alike.

http://www.harborfreight.com/7-function-multimeter-98025.html

http://www.harborfreight.com/7-function-digital-multimeter-69096.html

I'm tempted to either buy the same one, and put the old one in the box (had it for a few months) and return it or buy the second one that I don't have and keep it.

The one I have is the 69096 model.  But honestly..what's the difference?   The board is identical,  the case is identical,  the leads are identical.   Just go buy one for $2,  why bother to return anything.  I should have purchased 2 or 3 of these for $2.   They are somewhat unsafe meters,  but they appear to work pretty well.   It's hard to find just a panel meter from China for $2 let alone a complete meter that works.

Jeff

[Stonent]

True but the wandering all over the place makes me a bit irritated.  I took it to work for basic troubleshooting and have it on my desk.  That and since I paid more than $2 for it...

[Stonent]

I bought one of these last year from Harbor freight when it was on sale for $5. It seems that this meter is just a rebranded DT-830 as everything looks identical.

It does seem to have a rather strong resemblence to the Uni-T DT830b





There also appears to be another DT-830b that is unbranded that looks even closer.



The only thing I can see different in these meters is they took the off switch and moved it to the knob. And removed the battery tester.

I do like in the grey one how they actually put lines around hFE and encircled the transistor tester to indicate that's what hFE means.

The best variant has to be the "FUKE" DT-830b.

[(In)Sanity]

The best variant has to be the "FUKE" DT-830b.

   OK,  that's just hysterical. 

[Stonent]

The best variant has to be the "FUKE" DT-830b.

   OK,  that's just hysterical.

A little white pen could fix the word "FUKE" into something more descriptive.

[(In)Sanity]

A little white pen could fix the word "FUKE" into something more descriptive.

Perhaps they are just prepping you for what you might ultimately say while using their product.

[SeanB]

Followed by a thud and an ambulance perhaps.........

[(In)Sanity]

Followed by a thud and an ambulance perhaps.........

LOL,  no kidding. 

Let me list out the pro's and con's of this device. 

Pros:

• Good accuracy for the price. This is great to keep you from second guessing the meter and using it longer.
• LCD has good contrast.  This comes in handy when it's fallen down near your trasmission in your car and you have to use a flashlight to see the reading.
• Range selector switch hasn't fallen off yet.  This will save you the expense of a pair of locking pliars
• Plastic case screw holes come pre-split and cracked so you don't have to.
• The HFE test connector appears to have no noticeable contact resistance to help prevent you from wasting your time trying to use it.
• The test leads don't actually contain wire so the risk of electrical shock is minimized
• A convenient fuse has been provided which is built in to the test leads to protect the user from overloading the 10 amp current range.   This also doubles as a camp fire starter in the event your stranded and all you have is a car battery and your meter.
• The gracefully supplied battery has extra short life to prevent you from using this meter longer then needed.
• If you agree not to change the already short life battery you may receive a discount (or lack of an increase) in your life insurance policy rates.
• In the event your meter should expire (clearly do to your own incompetence) then the plastic shell can be melted down to make decorative candles for your home. 
• A large bright yellow on/off switch has been provided with a limited number of life cycles to further aide in reducing the time using this meter.

Cons:

I really can't think of any.

Jeff
 

[Bored@Work]

• The HFE test connector appears to have no noticeable contact resistance to help prevent you from wasting your time trying to use it.

But one contact is directly connected to one of the probe sockets. So if you have some transistor stuck in it, and then probe mains voltage you can easily do a haptic voltage check in parallel.

[Stonent]

I couldn't resist buying another one of these since they were $2.00 today. I purposely bought the "other" meter that has the red switch so we could compare the insides and see which may be better.

Here's the one with the "UL830B" from the teardown above.



And here's the one I bought. I'll call it "K2404":



1. Different pots.  Mine had about a 2 to 3 mm piece of bare tinned wire sticking out of the middle leg of the pot.  I snapped it off.
2. Mine has the hole on the left for the backlight button. There's another meter that looks like this one that has a backlight button. So I'm guessing mine is the same brand/source as that.
3. I've got a big ground area.
4. I've got a soldered fuse. 
5. Under the battery on mine is a + and - in the case showing the battery should be flipped the other way so the wires don't lay across the inputs and I'm assuming wires tucked away on the other side.  Sadly they did not install the battery correctly as you can see and caused a potential dangerous situation.
6. My test leads have 1000V melted in to them that looks like it was done with a cattle branding iron with gloopy plastic around it.
7. My capacitor appears physically bigger. It was marked ":N." and "154"
8. It looks like both boards were designed with the input jacks on the side and then were just snapped out and moved to the other side.

Anything else anyone notices to be different aside from board layout?

[Stonent]

Also the battery tester function... According to the insert it puts a 370mW load across the battery and checks the voltage drop.

[IanB]

Here's a picture of a 90899 from three or four years back:



I think the build quality might have been slightly better then?

1. There is a grounding spring on the PCB connecting to a shield inside the back cover
2. The 10 A shunt looks tidier
3. The DC trim pot is possibly of better quality?
4. I see a PTC marked below R4 and C2--is there one in the later model?

[(In)Sanity]

The one I got yesterday and have been talking about actually had the fuse holder soldered in at an angle.  Instead of fixing it they just rammed the fuse in and forced the blades way apart. I guess it technically worked..so they just went with it.   I was able to correct the issue in just a few seconds by just hitting it with the iron.   It's a $2 meter.........

Jeff

[Stonent]

Oh yeah, my meter did not have any foil inside the case.

[Stonent]

http://habometer.en.alibaba.com/product/558303742-213524963/Digital_multimeter_DT_830B.html



Looks like you can buy them in bulk for $2 to $2.50 (Yellow)

http://habometer.en.alibaba.com/product/558561950-213524963/Digital_multimeter_DT_830B.html?tracelog=cgsotherproduct1

Or 2.50 to 3.00 each for a red one that looks identical to the Harbor Freight one except for the brand being different.

[(In)Sanity]

Ohh and by the way I did measure 1000v DC with this thing and 500 VAC and it survived.   I guess I could try 750 VAC,  I don't however have a current controlled source for that high of voltage AC so I'm a bit worried    The 1000V DC was current limited to around 100ma.  Still very dangerous. 

Jeff

[rsjsouza]

5. Under the battery on mine is a + and - in the case showing the battery should be flipped the other way so the wires don't lay across the inputs and I'm assuming wires tucked away on the other side.  Sadly they did not install the battery correctly as you can see and caused a potential dangerous situation.

In both mine and IanB's two holes for the battery wires can be seen, but in yours I think someone goofed up on the drilling and broke the PCB in the corner close to the transistor testing socket. maybe that is why they put the battery in any position.

8. It looks like both boards were designed with the input jacks on the side and then were just snapped out and moved to the other side.

I haven't noticed that. Quite interesting.

I think the build quality might have been slightly better then?
4. I see a PTC marked below R4 and C2--is there one in the later model?

Wow, yours look much more acceptable than the newer ones. If you notice, the PCBs areas are being reduced at every assembly iteration, as well as the number of passive components... Incredible!
BTW, no PTCs in mine...

I have a Steren 602-010 (Mastech M830B, circa-2002) but it is completely different (all discretes):

[Stonent]

OK team I just got back with my Feng Shui master and we now have a change of plans... I want you design a multimeter and I want you to move the components as far as possible away from the center as possible.  Don't ask. Just do!

So I'm guessing the 830B model is more of a front face specification rather than an inside specification.

Just make it look like "this" and put whatever the hell you want inside.

[amyk]

I almost thought that link said "Hobometer"...

The selector switch is in the centre, that's why all the other components end up at the edges.

[rsjsouza]

So I'm guessing the 830B model is more of a front face specification rather than an inside specification.

Just make it look like "this" and put whatever the hell you want inside.

That is pretty much it. I was always told that the price of the plastic mold for the case is tremendously expensive, therefore they need to reduce the price on the internals to get the most out of the same mold.

DMMs are the cheapest ones, but I've seen this "design recycling" in other classes of instrumentation equipment as well... Not that this is a bad thing, but definitely the quality becomes a factor of manufacturing date, not model or revision.

All that, I still find incredible how they can still make money by selling these at US$2.00...

[saturation]

Did you hot air the PCB or the chassis?  If its the PCB that's impressive.  90F would simulate early summer, as in leaving the DMM in a car or such, and the fridge effect would be like working with it say, in your car, during the fall or 'warm' points of winter.

I just did a quick for fun test on this little guy.   It had been sitting all night in my basement lab at around 68F,  I used my hot air rework to slowly bring the thing up to around 90F and it only increased the least significant digit by 1.  That's a 0.1% increase.  Still not bad for a $2 meter.   I may do a more comprehensive test in the future instead of the quick and dirty test.

Jeff

[SeanB]

I must buy one tomorrow at the house of tat, Osmans clocks and watches. R42 each, in a blister pack. Check it out, tear it apart then freeze it to -13.4c in the freezer and check again. Single point check on 10V only, possibly a resistor as well.

[(In)Sanity]

Did you hot air the PCB or the chassis?  If its the PCB that's impressive.  90F would simulate early summer, as in leaving the DMM in a car or such, and the fridge effect would be like working with it say, in your car, during the fall or 'warm' points of winter.

I just did a quick for fun test on this little guy.   It had been sitting all night in my basement lab at around 68F,  I used my hot air rework to slowly bring the thing up to around 90F and it only increased the least significant digit by 1.  That's a 0.1% increase.  Still not bad for a $2 meter.   I may do a more comprehensive test in the future instead of the quick and dirty test.

Jeff

I applied hot air from a distance for some time to slowly warm the plastic case and also the inside indirectly.   It needs to be an even heat for a true test.

Jeff

[T4P]

i have several ... heat packs, those that you use during winter as a leftover from my japan trip
Would make a even heater for a tiny meter like this 
Or a peltier hot side bolted down to a steel plate covering the entire meter

[saturation]

Yes, but cold works as well, after all you're just looking for an  ambient different from standard, so why worry about heat? Just throw in into the refrigerator for an hour and see what happens.  You'll get a lot of condensation when you remove it, and that's another test right there.  1 hr, and that's all it takes.

I applied hot air from a distance for some time to slowly warm the plastic case and also the inside indirectly.   It needs to be an even heat for a true test.

Jeff

[(In)Sanity]

My little test was just quick and dirty,  hardly scientific.   I'd be interested to know just how much it drifts under a more controlled test.   Temperature coefficients and even thermal junctions are a subject of interest to me lately.   

Jeff

[(In)Sanity]

Ok,  in the interests of science...umm.. Yah something like that I've done some more thermal testing. 

Temperature as measured at the bottom of the 10 amp current jack with a Type K thermocouple and socked for at least half an hour at each temperature, here is what I've got.

Voltage reference was a fresh 1.5V AA battery. 

@ 102F (38.89C)  the meter reads 1.569 - 1.570 with flutter. 

@ 56F (13.33C) the meter reads 1.572 without much flutter.

So based on that test and temperature range it drifted 0.191%.  That's 0.0042% per deg/F or 0.0246% per deg/C or 246 ppm/C which if you think about it sounds about right for the type of components used.

Heating and cooling source provided by a 100W peltier with a feedback loop to the thermocouple.   It was just a quick toss together but appeared stable.   The meter was placed on top of the heating and cooling source and allowed to soak and stabilize.   Not exactly an environmental chamber,  but a test none the less.   I was having a hard time with cooling below the noted temperature with my current setup.  It's a $2 meter,  pretty damn stable for a $2 meter.

[mrflibble]

I noticed that in some of the meters IC1 is 44 pins, and in others it's 42 pin. Any idea what IC1 is? Any datasheet?

[amyk]

ICL7106 or equivalent.

[mrflibble]

ICL7106 or equivalent.

It is the "or equivalent" I am worried about. Case in point, I have the datasheet for the TelCom TC7106 in front of me and that is available in 40 pin dip (which is what is in my super old el cheapo DMM) and 44 pin PQFP/PLCC. And neither of these TelCom TC7106's has an RS-232 output as reported for the Cen-Tech. I'm interested in using the RS-232 port so if you or anyone else knows more specifics about that or what exact chippies are in the DMM's in this thread that would be real handy.

[sync]

I don't think the cen-tech has RS232. The hack (http://www.instructables.com/id/DMM-Piggyback-add-RS-232/) taps an analog signal and uses the microcontroller ADC.

[mrflibble]

I don't think the cen-tech has RS232. The hack (http://www.instructables.com/id/DMM-Piggyback-add-RS-232/) taps an analog signal and uses the microcontroller ADC.

That is indeed the hack I mean. And thanks for pointing that out. I guess this is a good example of why sleep is a good plan. I totally misread that yesterday. I mean, it's still a cute hack but less useful than I thought it was. Doh!  Guess it's back to my original plan of decoding the lcd outputs then. At least that piggyback hack did have some nice inspiration on decoding the rotary encoder.

[d3javu]

I have one made by pro's kit. It is my first ever multimeter which i use during my university years. 

[Jidis]

At the risk of being pelted with rocks, I had this opened and figured someone might want to see it. It should be the currently selling "no backlight" version. It's a model 69096. Board looks similar to the OP's, but not exactly.

I'm a fan of these things. I've got one of the black ones on the way here now (DT830D) with square wave and continuity functions. Need to get that yellow one next. There's also a DT830-CLOCK that's black with a yellow label. It appears to have reset and adjust buttons, but I'm guessing they might just be for the clock part. If anybody spots that on eBay or something, let me know.

Take Care

[retiredcaps]

I had this opened and figured someone might want to see it.

I'm always interested in seeing what the insides look like regardless of price or manufacturer.

Your Greenlee DM-55 is way better built compared to this.   

[Jidis]

Your Greenlee DM-55 is way better built compared to this.   

Yeah, I noticed that too. 

These pictures seem to show stuff my eyes have trouble seeing. Do you know if those Intersil,etc. chips make it very far up the multimeter ladder, or do they only show up in the ultra cheap stuff?

Take Care

[retiredcaps]

These pictures seem to show stuff my eyes have trouble seeing.

Yes, I have noticed that too.

Do you know if those Intersil,etc. chips make it very far up the multimeter ladder, or do they only show up in the ultra cheap stuff?

If you want to spend about 1.5 hour finding out how the 7106 came about read and listen to

https://www.eevblog.com/forum/testgear/old-fluke-multimeters/

http://www.theamphour.com/180-an-interview-with-dave-taylor-multi-talented-meter-maker/

[Jidis]

Much Thanks!

I got glued to that Fluke thread and couldn't get off of it.

Re: The HF meter- I notice there are 2 non-backlit versions on their site right now: My 69096, and a 98025. Neither of which is the OP's 90899. Specs look the same, but they added a "Frequency" spec of 45-150 Hz to the 98025. I also noticed last night that the one I cracked open (69096) is a rich darker red vs. the bright red plastic backlit model here. Reminds me of that Merlin game from back in the 70's.

I can see me years from now like you guys with the Fluke 806x collections, posting pictures of my army of DT830 clones. 

[Stonent]

Also the HF versions all have the battery tester where the others usually don't.

[Jidis]

Also the HF versions all have the battery tester where the others usually don't.

Yeah, it looks like most of them with that same enclosure have twenty positions for the switch, so I guess they have to make trade-offs. I do remember at least one of the yellow ones having the battery test down in the lower half of the dial somewhere. I also remember some others where certain positions actually shared a couple functions. Not sure how they handle that.

The reason I asked about those chips was that seeing all these different versions got me wondering if the same chip is capable of a much higher level of accuracy in a different circuit, and how much variance there might be between different revs of that PCB or different models of this clone. The one I checked here was surprisingly close to the values of the reference board I bought, but it would still be interesting to know if there's one specific brand/model which is consistently more accurate than the others.

Take Care 

[SeanB]

7106 in it's various varieties is a very good design, and is very accurate and linear, depending only on short term oscillator stability and 2 low leakage capacitors and 2 high stability resistors for operation, along with a good reference. The internal one is pretty good, so it is mostly the one used.

You get a 1999 count meter that will work from -1999 to +1999 with nearly perfect linearity and almost no offset, provided the supply is noise free and the layout is as recommended in the app notes ( and still good even without that to some extent), and the clock is a multiple of the local mains frequency. You normally get it set for 2.5 readings a second, which makes it reject both 50 and 60Hz noise. Only caveats is that you need to remember it is slow to come out of overload, and that the internal reference is limited in common mode range and the current it can supply. Also do not leave it in test mode for a long period as this damages the display.

[dannyf]

A big 830 fan here. I have always been amazed by what those little buggers can do.

[Jidis]

Thanks for the info SeanB!

I see there's another thread on it here. That guy's got mine, and I notice mine is missing a cap about an inch below the trim pot. Don't know if that's something they decided to stop using or if someone was just in a hurry when they did mine. My board isn't even silkscreened.

I also noticed the yellow one with the through hole parts in post #3 over there has what looks to be a 42? pin version of the chip rather than a 44, unless there's a couple which weren't dragged out to those pads.

George

PS- I got the "fall apart" test leads everyone talks about with this non-backlit one. They're different but still cheap looking on the other, so apparently it sells with a couple different types.

[Jidis]

Here's the bright red one (92020) with the backlight. The board in this looks very similar to the through hole yellow version that guy at BadCaps had. Some of the through hole parts are even in the same spots as mine, but I didn't want to pull the board out now to see if there are holes under them. This also has the 42 pads surrounding the processor (vs. 44).

Funny, but I ran into the same deal on that other one that someone joked about here with the "pre-cracked" threads. Almost all of them were cracked on the darker red one. The cracks don't seem to go all the way down (yet), so there's still something to grab. They're mostly where the threaded posts neck down to a smaller size at the top. That said, maybe the bright red one has softer plastic and is a better choice for longevity. Also, the owner of the yellow one mentioned the PCB being wedged in and not wanting to pry it out for risk of breaking it. My non-backlit had that too. It looks like they didn't cut the 'U' shaped notches in the board wide enough on mine to fit around the threaded posts. I Dremeled mine out before reassembly, but had also noticed a spot in the case where it looked like someone had dropped the soldering iron and didn't pick it up for a few seconds (there was even solder still smeared into the plastic). When I was putting it back together, I noticed that the melted dip in the plastic lands right on the post where the board is too snug. I think they got a batch of boards where the notch was too tight, so they squashed the iron into the case to make the post smaller. 

Good to know our three dollars goes to such innovative thinkers. 

[marshallh]

I've now had 2 of these types of meters blow their brains out when turned on. (I.e.  the glop top explodes and shatters itself).
They work great for low level DC work.

[Jidis]

Here's the board for the black DT-830D. Unfortunately, it's a DOA. In some modes, a character or two will show up on the display, but in many, it stays blank and there's no sign of life from the added continuity beeper, so I doubt it's just the screen. Soldering is somewhat messy as expected.

Interestingly, the board looks quite different from my others or any I saw online. There's a 358 opamp added, *no* DC trim pot, and the IC (chip on board thing) appears to be installed at an angle, with only 40 pads drawn from it (11-11-10-8). It's also got nice looking "hatched" patterns filling the empty spaces (grounded, I guess). The little daughterboard for the jacks is at a different height and is using three connecting wires as standoffs. Soldering for the wires looks like crap on the mainboard end. There's barely enough to fill the holes and the main V/mA one looks like it may already have broken free. Otherwise, it looks like a sturdier means of holding them. They sit lower than the mainboard, so that the back of the enclosure acts as a stop now when you press on them.

This is the model with the square wave output and continuity features. The diode test appears to share the setting for 2000 ohms. It's also got a battery compartment with spring clips in a unique "reverse polarity" configuration. There's also another unstuffed spot on here by the center hole. As with the other, I have no way to know if there was supposed to be a part there or if it was optional (no labels either). I'm guessing those three pads in the upper right with the 100 ohm resistor are where the trim pot went.

BTW, these pictures are sized and aligned so that if they're in the same location, you should be able to bounce between them with the pads and holes lining up (top layer is mirrored).

Take Care

PS@marshallh- Do you mean they blew up with nothing connected?

[retiredcaps]

Here's the board for the black DT-830D. Unfortunately, it's a DOA.

The first ever multimeter I bought was one of those DT-830 from ebay.  Not surprisingly, it arrived DOA.  If you flex the pcb around the COB, you can see more lcd segments, but nothing makes sense on any rotary dial setting.

I still have it in hopes of fixing it one day for educational purposes.

[Jidis]

If you flex the pcb around the COB, you can see more lcd segments, but nothing makes sense on any rotary dial setting.

Funny, I did the same thing with this one after noticing that it's got the same cracked threads issue as the dark red one. I thought maybe the LCD pad wasn't making contact with the board, but it turned out some weird area over on the edge of the board was the best place to flex. It still didn't bring it back to life or put anything worthwhile on the screen. Also, the original reverse polarity battery setup shows more life than the correct way. With the battery in backwards, you can get decimal points and an occasional "HV" or something.

Are those displays some sort of standard pinning? All I'm familiar with are those HD44780 ones, but I'm guessing those Intersil chips were setup to use something common.

I notice you saw this guys meter. It's weird that they use the same model numbers for a whole slew of different versions. His is also a "D", but it's nothing like mine.

Regarding some of those cases, I don't know why the heck they would keep using something which has proven to fail before it even reaches the customer. You'd think with all the changes in PCBs, they'd have redesigned or reenforced the threads somehow.

Take Care

George

PS- Sadly, I wasted about an hour tonight cleaning up and resoldering everything on that black one only to see it do the exact same thing afterward.

[Stonent]

I've had a couple of these where the zebra strip is the cause of the problems.  Commonly if the screws stripped out and there's not enough pressure being held on the display the numbers will go all wonky.

[Jidis]

Hi Stonent,

I suspected that as well, but I seem to get less activity from it when pressing near the strip than in other areas. Strange thing is, I can get random LCD segments to display like Retiredcaps mentions, but more so by simply touching certain areas of the PCB, rather than pressing. Like his though, it never really makes any sense, and if I short the probes in continuity mode, I can go around the board pressing and touching everything and it never makes a peep.

Still wondering about that LCD though. Is there some sort of standard for those things? Also been wondering why, with the few external components you typically see in these cheap meters, the DIY stuff you see using those ICs always seems so rudimentary. I didn't see one with anywhere near the range of functions these meters have.

George

[Stonent]

Hi Stonent,

I suspected that as well, but I seem to get less activity from it when pressing near the strip than in other areas. Strange thing is, I can get random LCD segments to display like Retiredcaps mentions, but more so by simply touching certain areas of the PCB, rather than pressing. Like his though, it never really makes any sense, and if I short the probes in continuity mode, I can go around the board pressing and touching everything and it never makes a peep.

Still wondering about that LCD though. Is there some sort of standard for those things? Also been wondering why, with the few external components you typically see in these cheap meters, the DIY stuff you see using those ICs always seems so rudimentary. I didn't see one with anywhere near the range of functions these meters have.

George

Well many meters use the ICL7106 chip or a clone living in the blob.  It has everything you need including LCD driver, with just a few passive parts on the outside.



There's like 5 caps and 5 resistors in total. 

There's also the 7107 which is the LED version.

[dannyf]

A good application with those meters is to repurpose them as dedicated volt or amp or ohm meters: take out the pcb and selectively solder the pcb traces to select the range / measurement type. This thing can be easily powered from a 12v source and you have a very accurate volt / amp or ohm meter.

or a frequency meter or capacitance meter (not so accurate).

[Jidis]

Well many meters use the ICL7106 chip or a clone living in the blob.  It has everything you need including LCD driver, with just a few passive parts on the outside.

Thanks Stonent. Yeah, I saw some of the example circuits for that chip, they're just never really specific about what lines are what. I also noticed that the meter's PCB has a much higher number of contacts for that zebra strip thing (something like 30?).

A good application with those meters is to repurpose them as dedicated volt or amp or ohm meters.

Only problem with that is that there seems to be a whole slew of those little mini panel meters already out there which sort of do the same thing, with the exception of the resistance measurements, but since it doesn't auto-range there, that would probably require a mess of switches or something.

Take Care

[CatalinaWOW]

Since the price of these things ranges from free to a couple of bucks, their best application is to solve the "Its never where I need it" problem.  I have a couple of dozen.  Just like the free flashlights from the same source.  They end up in each of my cars, in the kitchen drawer, by the computer, in the shop and so on. Don't worry about fuzes, batteries or anything.  I haven't had much problem fuzing the leads, but do break them regularly.  In any case, just like DOA, the solution is to fill the landfill and break out another one.

For the collectors out there, the most fun one I have seen got a packaging error.  Had a long list of functions that it supposedly could do, including capacitance, frequency, temperature etc.  Not bad for a free meter, but it was the same little unit.  I think I kept the packaging somewhere, but not with the meter inside, because I needed a meter NOW!

[Jidis]

For the collectors out there, the most fun one I have seen got a packaging error.

How about this one? Ran into it the other day and had forgotten I had it. I think it may be a miniature predecessor to those red things. It takes six of those AG13 type batteries and cost three bucks or something (probably less than the batteries). Unfortunately, it's also dead. 

[CatalinaWOW]

The little meter that "could".

See in the claims on the package that it has gained the ability to measure AC current, frequency, capacitance, humidity, sound level and luminosity.  Maybe that is what hfe translates into in Chinese.  Strange that temperature and inductance weren't on the list of things it can do.

[Stonent]

Yeah I posted a picture like that on the HF facebook page and asked them how to access the other functions and they just linked me to the manual.  When I tried to explain to them they just ignored me.

[amyk]

That's 12 functions, not 7... someone can't count.

[cosmicray]

That's 12 functions, not 7... someone can't count.

Of the 12 listed, there are 7 (by my count) that it actually can do.

[CatalinaWOW]

They had some moments of honesty.  You notice that to the left of the list of functions it identified as a 7 function meter.

I actually don't think direct dishonesty is involved.  Just a profound misunderstanding of western culture and English.  If you read Harbor Freight manuals you find many safety warnings that are just not applicable to the device in question.  An admonition to remove power before servicing a piece of hydraulic gear.  Someone somewhere had just enough knowledge to recognize that this product is a meter, and copied text from another meter.  Then moved on to a package for hog feed or whatever was next on the list.

You find the same kind of ignorance in tattoo shops and movie studios in the US, using strings of Chinese characters with at best a superficial understanding of what they say.  Selection is based on visual appeal as much as information content.

[IanB]

Harbor Freight does actually sell another meter with all those functions. It seems like someone accidentally put the right text on the wrong packaging.

[Stonent]

Harbor Freight does actually sell another meter with all those functions. It seems like someone accidentally put the right text on the wrong packaging.

Yeah I figured it was a packaging issue.

[rsjsouza]

I just got another free DT830 DMM from Harbor Freight and compared to one that I had got before with another purchase, and to my dismay the quality eroded even more...

In all pictures the newer model is on the left; the older on the right.

The two first pictures show how the packages changed, and in the back one can see the datecode between the two (45th and 1st weeks of 2014).




Pictures 3 (front fascia comparison), 4 and 5 (rotary dial detail of the newer and older models respectively) show the front fascia does not change much but scratches can be seen everywhere on the newer model.






Picture 6 shows the diferences on the grip of the back cover.


Pictures 7 and 8 . The most striking differences are the soldered fuse and the absence of a trimmer on the newer model. Interesting to see the newer model does not have part designators on the silk screen and it mentions DT833 with a March 2012 datecode. The older model shows LE830B with maybe a February 2012 datecode.





In any case, it is interesting to see how a few more cents can be shaved off every spin of a design...   

[SeanB]

Next rev they probably will go to losing that big copper pour, and the pads used for the non COB 7106 package, which probably is only used for functional testing of the board, so they probably will move to not testing the COB until final assembly if at all. You can even see how the later mould has a rougher inner finish, it has not been polished as much as the first mould set inside, and the ejection pins are a different type with much poorer surface finish.

[MaximRecoil]

In summary: do never put this DMM across the mains leads... It may be a shocking or explosive experience... It is fine for small electronics circuits, provided the loose spring is not shorting anything inside...

I've had my Cen-Tech multimeter for about 12 years, and I've measured mains voltage with it plenty of times:



They are also very accurate:



So maybe it's your Fluke that's off. I think it's funny that Dave constantly makes fun of the Cen-Tech in that video, yet he can't find any actual faults with it, and it's as accurate as his expensive equipment.

I'm on my second 9v battery; the original battery that came with it went dead a few years ago.

Not everyone has any use for the additional functionality of expensive (and big/bulky) multimeters, in which case, it would be a waste of money to spend more than a few dollars on one. I use mine mostly when working on my 1980s arcade machines (which is the reason I bought it in the first place) and my 1969 car. Voltage, amperage, and continuity/ohms are pretty much all I need.

The one thing I wish it had is an audible beep-on-continuity function, which would come in handy for testing fuses in a car. I have a more expensive multimeter that was given to me for free, which has that function, but the only time I use it is when I specifically want that beep function. Otherwise, the Cen-Tech is handier and more convenient to use.

[rsjsouza]

In summary: do never put this DMM across the mains leads... It may be a shocking or explosive experience... It is fine for small electronics circuits, provided the loose spring is not shorting anything inside...

I've had my Cen-Tech multimeter for about 12 years, and I've measured mains voltage with it plenty of times:

As I mentioned here, I also have a very similar 14 year old multimeter that is much better built when compared to the one I referenced in my original post. And yes, I have used it on higher voltages (not only mains) quite a few times.

They are also very accurate:

No contest here. This is simply due to the fact the 7106 IC is an extremely robust and accurate design.

So maybe it's your Fluke that's off.

Comparing oranges to.. Rocks?!? Different meters, originated from different dates, manufacturing plants...

I think it's funny that Dave constantly makes fun of the Cen-Tech in that video, yet he can't find any actual faults with it, and it's as accurate as his expensive equipment.

Well, I don't think anybody denies the relative accuracy of the meter - however, there are other factors to be taken into consideration. One, for example, is the reproducibility of results under different environments and among different production batches - I have had a few of these over the years and found them to have a wide variability straight out-of-the-box. Another is the lack of independent verification of their specifications - claims of withstanding 1kV when clearances and creepage are insignificant is a red flag. Another is the build quality and control - I had a loose spring on my meter straight out of the box, not to mention the sheer robustness of the casing, which is clearly incapable to resist more violent surges if they happen. All of these are very common detracting aspects of the 830-class meters.

Not everyone has any use for the additional functionality of expensive (and big/bulky) multimeters, in which case, it would be a waste of money to spend more than a few dollars on one. I use mine mostly when working on my 1980s arcade machines (which is the reason I bought it in the first place) and my 1969 car. Voltage, amperage, and continuity/ohms are pretty much all I need.

YMMV. I have used all my meters in several scenarios and have lost a few of them in stupid accidents, with varying degrees of damage (from internal electronics damage to broken enclosures). That is another aspect where these types of evaluations and criticism boil down to: accidents, which happen when you are most distracted and can have dire consequences depending on the total energy of the fault. Stating that a meter is safe or unsafe only by anecdotal evidence of your experience is not enough. That is why some folks disassemble them and point out the weak points.

The one thing I wish it had is an audible beep-on-continuity function, which would come in handy for testing fuses in a car. I have a more expensive multimeter that was given to me for free, which has that function, but the only time I use it is when I specifically want that beep function. Otherwise, the Cen-Tech is handier and more convenient to use.

Well a DT830D seems to have audible continuity.
 

[saturation]

The freebie Centech multimeter can measure mains, or more.  The likelihood of a consumer  experiencing an issue that would cause the meter to explode or injure its user is low, and it depends at what CAT level measurement is made.

But because DMM are used as general purpose tools to examine many types of faults, you never know when the critical fault will occur that it has no protection for.  For example, if used by a professional electrician,  the types of exposure are wider and riskier.

Toronto Ontario relatively recently [ compared to OSHA and the US] banned use of NRTL unlisted meters for professional contractor work.  Certified meters have all the protection built in.  Their pre-ruling stats are in this promotional brochure,  they say they had 26 reported DMM accidents in 8 years, and that is for all licensed contractors in Toronto.   Last I heard accident rates are down >>90% and are posted on their website.

The lesson is you can get away with it, but the accidents happen they are wholly preventable with a better meter.

I've used cheapos myself for 30+ years off on when didn't have my own DMM and had them fail less than a handful of times, and only 2x they smoked and died [ this is all back in the low tech setting of the Marianas. ]  They're more likely to drift off over time mostly from age or abuse.  But with my personal Fluke its never happened in the same period, 30 + years and I try to bring it everywhere it might be used to avoid such issues.  Its cheaper than seeing a doctor, even if rare, and so far, I can only die once.

[MaximRecoil]

As I mentioned here, I also have a very similar 14 year old multimeter that is much better built when compared to the one I referenced in my original post. And yes, I have used it on higher voltages (not only mains) quite a few times.

What is the basis of your assertion that the one pictured in your original post shouldn't be used for mains voltage? Have you tried it?

Comparing oranges to.. Rocks?!? Different meters, originated from different dates, manufacturing plants...

No, it is not an invalid comparison. I am comparing accuracy to accuracy. That's like saying you can't compare the accuracy of a given Rolex to a given Timex because they are different watches, originated from different dates, manufacturing plants ...

Well, I don't think anybody denies the relative accuracy of the meter - however, there are other factors to be taken into consideration. One, for example, is the reproducibility of results under different environments and among different production batches - I have had a few of these over the years and found them to have a wide variability straight out-of-the-box. Another is the lack of independent verification of their specifications - claims of withstanding 1kV when clearances and creepage are insignificant is a red flag. Another is the build quality and control - I had a loose spring on my meter straight out of the box, not to mention the sheer robustness of the casing, which is clearly incapable to resist more violent surges if they happen. All of these are very common detracting aspects of the 830-class meters.

That's neither here nor there. The fact is, he was poking fun at it even though there was no basis for it in his video.

Well a DT830D seems to have audible continuity.

Nice. The DT-838 has it too. In fact, it looks like the DT-838 is the cream of the Cen-Tech (or might as well be Cen-Tech) crop, as it has a temperature testing function as well. It's about $7 shipped; I might give one a try.

Edit: Better yet, $4.79 shipped. I just ordered one.

[rsjsouza]

As I mentioned here, I also have a very similar 14 year old multimeter that is much better built when compared to the one I referenced in my original post. And yes, I have used it on higher voltages (not only mains) quite a few times.

What is the basis of your assertion that the one pictured in your original post shouldn't be used for mains voltage? Have you tried it?

Well, I don't think anybody denies the relative accuracy of the meter - however, there are other factors to be taken into consideration. One, for example, is the reproducibility of results under different environments and among different production batches - I have had a few of these over the years and found them to have a wide variability straight out-of-the-box. Another is the lack of independent verification of their specifications - claims of withstanding 1kV when clearances and creepage are insignificant is a red flag. Another is the build quality and control - I had a loose spring on my meter straight out of the box, not to mention the sheer robustness of the casing, which is clearly incapable to resist more violent surges if they happen. All of these are very common detracting aspects of the 830-class meters.

Keep in mind that not everyone disassembles their meter to look inside for loose things or has other meters to double-check if its readings are accurate.

Comparing oranges to.. Rocks?!? Different meters, originated from different dates, manufacturing plants...

No, it is not an invalid comparison. I am comparing accuracy to accuracy. That's like saying you can't compare the accuracy of a given Rolex to a given Timex because they are different watches, originated from different dates, manufacturing plants ...

Perhaps I read your statement wrong. What I read is that you suggest the Fluke is off based on the argument the 830s are accurate and even included a picture to show your meter as being spot on (which is coming from a different manufacturer and batch). That is what I think is an invalid comparison. 

That's neither here nor there. The fact is, he was poking fun at it even though there was no basis for it in his video.

I don't know about what Dave commented on which video; I can only speak for my post.

[rsjsouza]

A bit of a necroposting here...

I decided to see how Mastech has distanced themselves from their original M830B design and got a MAS830L. Its main differences are:
- Maximum of 600V for both DC and AC
- Claims CAT II 600V on the V/ohms/mA input
- Has a nice white backlight, but it only lasts for 5s
- Has decent banana jacks
- Has quite good silicone probes

[nick_shl]

Got one for free. At home found that they made it safer!
"If you can add protection circuit, replace front panel sticker!" - perfect logic in this case.
Now only 5A and "High Voltage" is 250V instead 1000V DC/750V AC

[rsjsouza]

Got one for free. At home found that they made it safer!
"If you can add protection circuit, replace front panel sticker!" - perfect logic in this case.
Now only 5A and "High Voltage" is 250V instead 1000V DC/750V AC

Thanks for the photos. In my opinion this is a very welcomed change to the meter. I am really not opposed to having a meter cheaply built, but instead one that tries to cheat on its specifications and lie to the unsuspecting buyer. These meters work really well for general low power usage.

[rsjsouza]

For others following this thread... joeqsmith put one of these under 1kV AC and DC.


As a bonus... A Brazilian talk show host tried to use one, but their crew did not do their homework in teaching her how to use it

[joeqsmith]

The one used for this video, which reads high, no longer has an adjustment.  Not that it matters.  The small peanut fuse was not soldered on one side, unless you consider a glob on one lead that makes no contact with the pad a solder joint.   I think the ZT102 is a better buy.

[rsjsouza]

The one used for this video, which reads high, no longer has an adjustment.

Just like some of the newer meters on this thread.

Not that it matters.  The small peanut fuse was not soldered on one side, unless you consider a glob on one lead that makes no contact with the pad a solder joint.   I think the ZT102 is a better buy.

That is hilarious, and exactly what I commented in your thread: the lack of quality control is my primary concern on new meters.

The MAS830L I mentioned above came with a loose rotary switch spring contact - it was an extra contact, not that it had become loose.

[AlienRelics]

I would not use one of these without first opening it up to check the construction. Solder balls, solder smears threatening to short things catastrophically.

I figure eventually those solder blobs bridging the banana connectors with the main board are going to crack and fail.

[rsjsouza]

I would not use one of these without first opening it up to check the construction. Solder balls, solder smears threatening to short things catastrophically.

I figure eventually those solder blobs bridging the banana connectors with the main board are going to crack and fail.

Exactly. I wouldn't either.

[6PTsocket]

I read off the wrong end of the rotary switch on my red one and ended up blasting OHMS with 120VAC. Everything but ohms still worked. The ohms scales just showed "1". I figured that meant the chip survived but was not talking to the outside world. A quick check of the resistors found R13 blown (open) and semi unreadable. Some nice fellow in the UK posted photos of every section of the board to show every resIstor big enough to read. R13 is marked 152 for 1500 ohms. I tacked in a 1/4 watt leaded resistor and I was back in business. SMD resistors on ebay were $1.37 a 100 but I didn't want to wait for an e packet from China.

Sent from my SM-G900V using Tapatalk

[6PTsocket]

In summary: do never put this DMM across the mains leads... It may be a shocking or explosive experience... It is fine for small electronics circuits, provided the loose spring is not shorting anything inside...

I've had my Cen-Tech multimeter for about 12 years, and I've measured mains voltage with it plenty of times:

As I mentioned here, I also have a very similar 14 year old multimeter that is much better built when compared to the one I referenced in my original post. And yes, I have used it on higher voltages (not only mains) quite a few times.

They are also very accurate:

No contest here. This is simply due to the fact the 7106 IC is an extremely robust and accurate design.

So maybe it's your Fluke that's off.

Comparing oranges to.. Rocks?!? Different meters, originated from different dates, manufacturing plants...

I think it's funny that Dave constantly makes fun of the Cen-Tech in that video, yet he can't find any actual faults with it, and it's as accurate as his expensive equipment.

Well, I don't think anybody denies the relative accuracy of the meter - however, there are other factors to be taken into consideration. One, for example, is the reproducibility of results under different environments and among different production batches - I have had a few of these over the years and found them to have a wide variability straight out-of-the-box. Another is the lack of independent verification of their specifications - claims of withstanding 1kV when clearances and creepage are insignificant is a red flag. Another is the build quality and control - I had a loose spring on my meter straight out of the box, not to mention the sheer robustness of the casing, which is clearly incapable to resist more violent surges if they happen. All of these are very common detracting aspects of the 830-class meters.

Not everyone has any use for the additional functionality of expensive (and big/bulky) multimeters, in which case, it would be a waste of money to spend more than a few dollars on one. I use mine mostly when working on my 1980s arcade machines (which is the reason I bought it in the first place) and my 1969 car. Voltage, amperage, and continuity/ohms are pretty much all I need.

YMMV. I have used all my meters in several scenarios and have lost a few of them in stupid accidents, with varying degrees of damage (from internal electronics damage to broken enclosures). That is another aspect where these types of evaluations and criticism boil down to: accidents, which happen when you are most distracted and can have dire consequences depending on the total energy of the fault. Stating that a meter is safe or unsafe only by anecdotal evidence of your experience is not enough. That is why some folks disassemble them and point out the weak points.

The one thing I wish it had is an audible beep-on-continuity function, which would come in handy for testing fuses in a car. I have a more expensive multimeter that was given to me for free, which has that function, but the only time I use it is when I specifically want that beep function. Otherwise, the Cen-Tech is handier and more convenient to use.

Well a DT830D seems to have audible continuity.

There are a lot of versions of the DT830 besides the HF freebee. I think somebody added a continuity beeper to an HF.

Sent from my SM-G900V using Tapatalk

[rsjsouza]

I read off the wrong end of the rotary switch on my red one and ended up blasting OHMS with 120VAC. Everything but ohms still worked. The ohms scales just showed "1". I figured that meant the chip survived but was not talking to the outside world. A quick check of the resistors found R13 blown (open) and semi unreadable. Some nice fellow in the UK posted photos of every section of the board to show every resIstor big enough to read. R13 is marked 152 for 1500 ohms. I tacked in a 1/4 watt leaded resistor and I was back in business. SMD resistors on ebay were $1.37 a 100 but I didn't want to wait for an e packet from China.

I have seen it happen with another meter, but in that case it was fatal: the black blob had the typical hole on one of its edges, caused by excess temperature. I wish I had taken a photograph.

There are a lot of versions of the DT830 besides the HF freebee. I think somebody added a continuity beeper to an HF.

The only one I know is a different model altogether:
https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html

[6PTsocket]

I read off the wrong end of the rotary switch on my red one and ended up blasting OHMS with 120VAC. Everything but ohms still worked. The ohms scales just showed "1". I figured that meant the chip survived but was not talking to the outside world. A quick check of the resistors found R13 blown (open) and semi unreadable. Some nice fellow in the UK posted photos of every section of the board to show every resIstor big enough to read. R13 is marked 152 for 1500 ohms. I tacked in a 1/4 watt leaded resistor and I was back in business. SMD resistors on ebay were $1.37 a 100 but I didn't want to wait for an e packet from China.

I have seen it happen with another meter, but in that case it was fatal: the black blob had the typical hole on one of its edges, caused by excess temperature. I wish I had taken a photograph.

There are a lot of versions of the DT830 besides the HF freebee. I think somebody added a continuity beeper to an HF.

The only one I know is a different model altogether:
https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html

The HF is the DT830B. The DT830D has a continuity buzzer. The buzzer symbol is shown in the same position as the diode test.

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