Author Topic: Harbor freight Cen-tech 90899 small teardown  (Read 37963 times)

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Offline Stonent

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #75 on: February 20, 2015, 04:57:52 pm »
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.
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Offline amyk

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #76 on: February 21, 2015, 01:47:42 am »
That's 12 functions, not 7... someone can't count.
 

Offline cosmicray

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #77 on: February 21, 2015, 02:19:49 am »
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.
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Offline CatalinaWOW

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #78 on: March 05, 2015, 03:44:35 pm »
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.
 

Offline IanB

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #79 on: March 05, 2015, 03:59:50 pm »
Harbor Freight does actually sell another meter with all those functions. It seems like someone accidentally put the right text on the wrong packaging.
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Offline Stonent

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #80 on: March 05, 2015, 04:10:16 pm »
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.
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Online rsjsouza

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #81 on: April 20, 2015, 05:32:37 am »
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...   :P
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Offline SeanB

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #82 on: April 20, 2015, 05:44:09 am »
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.
 

Offline MaximRecoil

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #83 on: December 10, 2016, 12:13:18 am »
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.
 

Online rsjsouza

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #84 on: December 10, 2016, 03:13:30 am »
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. :)
 
« Last Edit: December 10, 2016, 04:00:58 am by rsjsouza »
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Offline saturation

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #85 on: December 10, 2016, 03:22:31 am »
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.
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Offline MaximRecoil

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #86 on: December 10, 2016, 05:19:30 am »
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?

Quote
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 ...

Quote
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.

Quote
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.
« Last Edit: December 10, 2016, 05:35:18 am by MaximRecoil »
 

Online rsjsouza

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #87 on: December 10, 2016, 11:18:20 pm »
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.

Quote
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.
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Online rsjsouza

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #88 on: September 08, 2017, 09:43:46 pm »
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
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Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline nick_shl

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #89 on: March 10, 2018, 01:47:17 pm »
Got one for free. At home found that they made it safer! :-DD
"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
 
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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #90 on: March 11, 2018, 02:27:59 am »
Got one for free. At home found that they made it safer! :-DD
"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.
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Online rsjsouza

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #91 on: June 12, 2018, 03:54:39 am »
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
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Offline joeqsmith

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #92 on: June 12, 2018, 07:51:39 pm »
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.
How electrically robust is your meter?? http://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Online rsjsouza

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #93 on: June 12, 2018, 09:36:00 pm »
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.
:-DD 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.
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Offline AlienRelics

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #94 on: June 26, 2018, 02:14:22 pm »
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.
 
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Online rsjsouza

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #95 on: June 27, 2018, 12:18:44 am »
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.
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Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline 6PTsocket

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #96 on: August 26, 2018, 07:40:55 am »
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.

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Offline 6PTsocket

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #97 on: August 26, 2018, 07:44:39 am »
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.

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #98 on: August 26, 2018, 08:32:50 pm »
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
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Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline 6PTsocket

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Re: Harbor freight Cen-tech 90899 small teardown
« Reply #99 on: August 27, 2018, 12:58:32 pm »
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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