Habor Freight giveaway DMM test

[Fungus]

The biggest problem is the test leads breaking.

The secret is to squirt some hot glue into the top of the probes (the open tube part).

[rhb]

They already did. Check: https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg655719/#msg655719

Harbor Freight stuff has "Item Numbers".  There are at least 5 different item numbers for these free meters, I assume there are at least 5 different manufactories making them and they buy from whomever offers the lowest price.

I figured out how to add a trim pot to to item number 98025 if anyone's interested.

It worked for me, no guarantee.

Thanks,  That's the one with the worst error.  It's also the higher priced version with the backlight which usually is not a giveaway. .  I suspect that the item number is a single purchase order by HF.  Manufacturer may or may not change.  That provides everyone flexibility to modify designs and or suppliers.

[james_s]

No idea. The ones I found on Taobao either have Intersil logo (with a note saying it is a clone) or no logo at all.

LOL they clone the Intersil logo and then include a note that it's a fake part?  How very polite of them

[AtLarge]

The picture of the one with the backlight button is interesting.  Never saw one like that before and I have been stacking them up for a few years now.  I see you can get virtually the same DMM at Wally World now if you actually want to pay for one.  They are in Chartreuse and marked as AllSun.  They even had one on the rack with a GE logo but, exactly identical.     Wonder if that was an authorized version. 

[IanB]

The picture of the one with the backlight button is interesting.  Never saw one like that before and I have been stacking them up for a few years now.

I've seen many of the backlight ones in HF in the past. Usually they are priced a few dollars more and sold alongside the ones with no backlight.

[joeqsmith]

My free gift of choice at HF is the DMM.  I've given away quite a few, but I have 8 of the current red versions.  I just tested 8 of them against an LM399 voltage reference. 
.....

My reason for doing this is my concern that the voltnut aberration latent in many of us leads beginners on tight budgets to spend more on DMMs than they should.  If you're building things using 5% resistors and 10% capacitors you don't need a 0.01% DMM.

In many ways, these are much better than the first new analog meter the I owned.  As a beginner, I was not concerned with static.  Some of the cheap meters like these are easily damaged with ESD.      I damaged the analog meter several times and was able to repair it where the modern cheap meters are disposable.  No need for a battery to make voltage and current measurements was a plus as well. 

As a beginner, I certainly would have had no need for a higher end meter.  I would say having a meter like the free HF meter may have inhibited my growth.  If I knew every time I was going to play with it it may fail and I would need to replace it, I may not have played with electronics as much as a did. 

[rhb]

I've had one meter out of a dozen or so in regular use over many years (not the ones I tested).  Only one died.  No idea of the cause.

They certainly are not susceptible to damage from being dropped.  That's the main risk of damage to an analog meter.  I'd toss a DMM to someone on a roof.  I'd *never* do that with a VOM.

[joeqsmith]

I've had one meter out of a dozen or so in regular use over many years (not the ones I tested).  Only one died.  No idea of the cause.

They certainly are not susceptible to damage from being dropped.  That's the main risk of damage to an analog meter.  I'd toss a DMM to someone on a roof.  I'd *never* do that with a VOM.

I would imagine how long the meter lived will has a lot to do with how it was used and how much.  As a beginner, I did not have a lot of respect for the bits of equipment I had.   The meter was still working when I finally pitched it.  The case was badly damaged.  The plastic lens over the movement had a large section broke out.   It had been glued one too many times.   I guess a testament to Radio Shack.         

For me personally as a beginner, it was the meter's resistors that took the blunt of my lack of an education.   The leads took a fair amount of abuse as well.   

[6PTsocket]

Is it "classic" ICL7103 based unit?

Yes. If you search "DT830"you will see the meter. They are sold World wide and there are quite a few variants. One article I found was from the UK.

Sent from my SM-G900V using Tapatalk

[6PTsocket]

There is a lot of info on that meter under DT830. That is the chip under the blob and there are plenty of schematics of the meter.

I've never opened one up but I'd bet money it's a "classic" black blob of epoxy over an unknown die unit. Who can say what the IC actually is?

Sent from my SM-G900V using Tapatalk

[6PTsocket]

My free gift of choice at HF is the DMM.  I've given away quite a few, but I have 8 of the current red versions.  I just tested 8 of them against an LM399 voltage reference. 
.....

My reason for doing this is my concern that the voltnut aberration latent in many of us leads beginners on tight budgets to spend more on DMMs than they should.  If you're building things using 5% resistors and 10% capacitors you don't need a 0.01% DMM.

In many ways, these are much better than the first new analog meter the I owned.  As a beginner, I was not concerned with static.  Some of the cheap meters like these are easily damaged with ESD.      I damaged the analog meter several times and was able to repair it where the modern cheap meters are disposable.  No need for a battery to make voltage and current measurements was a plus as well. 

As a beginner, I certainly would have had no need for a higher end meter.  I would say having a meter like the free HF meter may have inhibited my growth.  If I knew every time I was going to play with it it may fail and I would need to replace it, I may not have played with electronics as much as a did.

One of my freebees, an old yellow one says Mastech on the pc board. There is a foil shield on the inside of the back cover and a spring on the pc  board to contact the shield. At one time they gave a little thought to ESD.

Sent from my SM-G900V using Tapatalk

[rhb]

FWIW My most recent one doesn't have a trim pot :-(

[james_s]

Is there a spot for one, or did they change the design to rely purely on tolerances of the components used or some kind of digital calibration?

[rhb]

Here's a family portrait.  The two on the left are the most recent arrivals. I have 4 more of the 90899s and confirmed that all are the same as the example in the photo.

While they generally look the same, all the front panels are slightly different except for the 98025 and the 90899.

Also, the recent versions only go to 250 V.  Some time when I don't want to do anything, I'll round up as many of the yellow ones as I can find and add pictures of those and measurements of my DMMCheck Plus.

[rsjsouza]

While they generally look the same, all the front panels are slightly different except for the 98025 and the 90899.

Thanks for sharing a more recent comparison. Those were my observations as well:
https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg655719/#msg655719

Also, the recent versions only go to 250 V.

IMO this is a good change (also reported by someone on the thread I linked above), as it is a bit more honest about the device's limitations.

[rhb]

I wouldn't be worried about using one at 500 V, but I wouldn't trust the probes that come with them.

I'm a little disappointed by the loss of the trimmer.  It will be interesting to see how accurate the 63759 version marked DT833 is. The high current fuse was reduced from 0.085" to 0.050" in the 250 V versions.

[6PTsocket]

Here are two older yellow models.  The first is the rotary switch OFF. The second is identical to the red one on the outside. It appears to be the same mold, just different color plastic.

In another post a fellow member displayed his red collection. There appear to be a bunch of production changes: fuse, no fuse, trim pot, no trim pot, board layout changes, circuit changes, etc. The same applies to the yellows. The early ones had a lot of film resistors instead of SMD's. There are also all the letter variants with features not offered at HF. From this site I learned about the "blob". I assumed they were hiding the chip. I never knew you could make a chip integral to the board, with no case and  cover it with epoxy.

Sent from my SM-G900V using Tapatalk

[rhb]

All the ones I've seen are fused.  I think people are confused by the 5/10 A fuse because it's not encased in glass. Though at 10 A I suspect the test leads provided would be the fuse if you were foolish enough to use them to measure that much current.  More recent versions have a wire leaded  fuse soldered in place.

[besauk]

They already did. Check: https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg655719/#msg655719

Harbor Freight stuff has "Item Numbers".  There are at least 5 different item numbers for these free meters, I assume there are at least 5 different manufactories making them and they buy from whomever offers the lowest price.

I figured out how to add a trim pot to to item number 98025 if anyone's interested.

It worked for me, no guarantee.

Was the 10K resistor also needed?

[james_s]

In another post a fellow member displayed his red collection. There appear to be a bunch of production changes: fuse, no fuse, trim pot, no trim pot, board layout changes, circuit changes, etc. The same applies to the yellows. The early ones had a lot of film resistors instead of SMD's. There are also all the letter variants with features not offered at HF. From this site I learned about the "blob". I assumed they were hiding the chip. I never knew you could make a chip integral to the board, with no case and  cover it with epoxy.

Chip-On-Board (COB) has been around for many years. Loads of electronic toys from the 1970s on have been made that way, virtually all inexpensive calculators, musical greeting cards, etc.

[rhb]

I just went through and did a cal on all mine that had a pot using my DMMCheck Plus.  Much to my surprise, I discovered quite a bit of variation in units with the same lot #. I've attached a photo of the others.

Most were already within 0.2% which is as close as they will read with a 5 V input.  They are really tricky to trim as breathing on the trimmer is too much.  I suspect that trying to do better would drive a person crazy.

[IanB]

I just went through and did a cal on all mine that had a pot using my DMMCheck Plus.  Much to my surprise, I discovered quite a bit of variation in units with the same lot #. I've attached a photo of the others.

Most were already within 0.2% which is as close as they will read with a 5 V input.  They are really tricky to trim as breathing on the trimmer is too much.  I suspect that trying to do better would drive a person crazy.

I have a few older ones with a trim pot. All of mine were a bit off at 5 V when tested out of the package and could be adjusted to do better.