Harbor Freight CenTech P37772 aka Mastech M9508 Teardown - Page 1
Forum section: electronics / general

author: PedroDaGr8
author_rank: Super Contributor
timestamp: December 05, 2012, 02:48:57 am
content: So I was walking through Harbor Freight Tools recently and came across this meter. It is the Cen-Tech P37772, which is really a rebranded Mastech M9508. Heck, even the leads say Mastech on them. It was $16 after a coupon so I figured what the hell. Why not? At best I'll have a beater meter; at worst I'll have something to post on here for us to ridicule. So I grabbed it.I don't want to spoil the fun so I will post images and typing commentary as I go.Well lets take a look at this beast!Quite frankly I am going to call this thing the Fisherprice meter because quite simply that's what it feels like. The red rubber case has that Playschool/Fisherprice kind of feel and the black plastic isn't any better. It feels almost like that black plastic they used to make VHS cassette tapes out of. Every gram of this thing screams cheap cheap cheap.Let's turn it on. Note that this one has a dedicated on-off button, not an on-off location for the dial. The display is nice and clear and large. Though the markings that show the units are ridiculously small. We can see clearly the meter does AC and DC voltage, AC and DC current, capacitance, temperature, resistance, frequency and hFE. Let's take a quick look at those jacks (the incorrect colors of the jacks is my fault, it was originally correct)Oh damn! Let's hope that is a mistake. No fuse on the 20A line! Also, note they don't even bother TRYING to fake CAT ratings. They just say their maximum rated voltages. Sure it will take that max voltage once, before it dies a fiery death (or worse).Let's take a look at the back. Nice cheap mounts for holding the probes. Note the lack of a stand, how do you view the screen when the meter is sitting on a table?Ta-da! Why use a stand when you can make the display rotate instead? To me this actually isn't a bad idea, the rubber should provide a good amount of friction to keep the meter from sliding everywhere when you change ranges. Too bad the hinge and what not feel very cheap as they rotate through their notched positions.Did I mention this thing is LARGE! This is it compared to my UT61E. Maybe if we removed the crap rubber sleeve.Nope still a beast, just an even cheaper feeling beast. This thing feels LIGHT, cheap and like crap. There is not much to instill confidence here so far. I'm not kidding when I say the rubber case makes up at least a third of the weight of the meter.Well let's take a look at the back. Oh, how cute the QC sticker stuck properly so it passed QC. At least there is a bit of humor in the warning label.This instrument contains no serviceable parts. Screw removal by qualified persons only.Last time I checked 9V batteries are user serviceable.Yeah, there is no battery door so you HAVE to remove the screws to change the battery. Since I know how to use a screwdriver (as well as drink one), I'm therefore qualified. Let's remove the screws.Hey, look at those small screws. Wait a minute, these don't look like the self-tappers found on most meters. Either they are using std screws into plastic (considering the cheapness of this meter very possible) or they actually splurged for brass inserts.WTF, they actually splurged for brass inserts.Actually, they use brass inserts (or nuts) for ALL of the screws in the entire meter except for the two which hold the LCD display module to the board (which may be because of clearance issues). There are two circuit boards. We also can clearly see the Mastech Logo and M9508 model number printed on the circuit boards. Note, the start point of the 9V battery leads on the right side of the image.Now we see the whole layout. Yep, one lonely glass fuse. Also, note that crazy long battery cable, it goes right by the unfused 20A connector. Plus it has a tendency to get caught in the slot on the body that allows the two halves to come together. This is incredibly unsafe, I can just imagine the 9V connector getting frayed by getting caught in the halves then jumpering a trace. Really safe! Yet hey they used brass inserts.Why you wouldn't use self tappers and instead use that money to provide a second fuse is beyond me. Maybe its just on the other side, though I severely doubt it. Also, that second circuit board appears to mainly serve the sole purpose of selecting the proper units on the LCD. One again a really confusing design choice. Why not cut the second board and figure out another way to route your display trace.With the second PCB removed we see this side is completely void of components other than the glass fuse. Lots of stray flux on the board it looks like NO attempt was made to clean the board at all. Those copper "connectors" are not held in place by anything other than pressure from the board on top. They fall out VERY easily. If one is in the wrong place the display goes crazy.On the board we have a bunch of opamps, a CMOS time base, a variety of precision MELF resistors (most are 0.25% or so). Most of the soldering appears reasonably clean with no botch jobs. It does appear two types of solder were used, the stuff that is SMD appears to be lead free solder (that or they all have cold solder joints) but the stuff that is through hole appears to use lead solder because it is VERY shiny.Not surprisingly, in general the meter looks very cheaply made.As for how does this meter meet its specs. It seems to meet it well for capacitance, though it maxes out at a lowly 2uF (not really very useful). That being said, I didn't bother testing much more due to how unsafe it is in general.They always say to leave the best for last. So I did just that. What's the best you ask? The test leads! They are mastech branded and are a bit shorter (i'd say 15cm shorter than the ones that come with the UT61). That being said they feel pretty nice and the point on them is needle sharp(I drew blood being careless with one uncapped in a bag). While checking them out I noticed some writing on the wire. At first glance I just saw the CatII 1000V, though yeah right, considering the crap inside the meter. Later while looking at the wires I saw 2000V and started laughing. It wasn't until the other day I spotted the backwards UR. So I decided to take a closer look. Sure enough I found not only the E-Number (E229772) which corresponds to DONGGUAN HUAYI MASTECH CO LTD but also a document number (1803). Clicking on that link we see the wire is clearly UL rated fr 2000 Vac/dc up to 85oC. A nice find for sure, it means at minimum at least the wire is decent quality.The most interesting thing to me is their internal resistance. It is HALF of the internal resistance of the Uni-T test leads. Sure the Uni-T test leads are longer but not near enough to double the internal resistance. The Uni-T test leads read around 120mOhms internal resistance on my UT61E while the Mastechs show around 60mOhms.All in all the test leads are the only thing worht anything out of this meter. The rest is a big piece of crap.

author: FenderBender
author_rank: Super Contributor
timestamp: December 05, 2012, 04:11:39 am
content: Heap of shit. But you're right. They're expenses seem to have been in the wrong places...

author: rsjsouza
author_rank: Super Contributor
timestamp: December 05, 2012, 04:40:14 am
content: It seems we coordinated the reviews... I just did a small teardown of another Cen-Tech DMM and saw yours when I was starting the post. Checkhere.

author: retiredcaps
author_rank: Super Contributor
timestamp: December 05, 2012, 06:11:21 am
content: Quote from: PedroDaGr8 on December 05, 2012, 02:48:57 amThanks for the review and teardown. I always wondered if those Mastech rubber holsters fit Fluke 80 series multimeters.Since I have no Harbor Freight in Canada and their manual does not state the dimensions, do you know?

author: PedroDaGr8
author_rank: Super Contributor
timestamp: December 05, 2012, 06:53:36 am
content: It doesnt but heres the dimensions:external width 95.5mmexternal length 200mmexternal height 44mmInternal: Best attempt made at dimensionswidth 88-90mmheight 38mmlength 180-190mm

author: T4P
author_rank: Super Contributor
timestamp: December 05, 2012, 08:20:15 am
content: All cheap and crappy multimeters come with no fuses on the amp side ...The leads are surprising in their own right though, it really is.But the expenses are indeed in the wrong places, like, the UTL-21 in china is veryyyy CHEAP. Something like about 1.20SGDBut the Mastech one on the other hand ... I have no idea but certainly about 3SGD

author: saturation
author_rank: Super Contributor
timestamp: December 05, 2012, 03:39:22 pm
content: Thanks for the tear down, certainly concerning. I would raise concern too over that Uni-T 16e meter shown as comparison, although better made, I'd downgrade the marks on those inputs to those of the EU version, as discussed here:https://www.eevblog.com/forum/reviews/uni-t-ut61e-multimeter-teardown-photos/msg165693/#msg165693And in Kiriakos site, with photos:http://www.ittsb.eu/forum/index.php?topic=322.0

author: PedroDaGr8
author_rank: Super Contributor
timestamp: December 05, 2012, 05:06:55 pm
content: Quote from: saturation on December 05, 2012, 03:39:22 pmOh I completely agree on derating the Uni-T ratings. They are definitely over ambitions, if not outright fraudulent, but for 99% of hobbyists even the current derated values are more than enough.As for Kirakos I respect him but he very much has a bee-in-his-bonnet over the UT61E. He is insistent that unless it meets the specs of a $300 meter it isn't good enough for anyone. Everything has its place, for me the UT61E even at its derated values is more than enough.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: December 05, 2012, 07:20:02 pm
content: Quote from: T4P on December 05, 2012, 08:20:15 amOK, its funny I have already blown the 200mA fuse. Trying to measure the current on one of those cheapy 10 5mm led flashlights. It turns out they run those LEDs at over 200mA (212mA according to my UT61E but keep in mind its likely higher than that after you factor in burden voltage).Otherwise the meter basically is the intellectual equivalent of going full-retard (this quote is from a movie). It's just weird the choices they made. Machined pin sockets for the transistors when a simple female header would work. Brass inserts everywhere. Then combine that with cheap housing, weird display, etc. I just don't get it.As for cost of the test leads, here prices vary so widely I can't say which is more expensive. Plus I can't see if the cheaper Mastech test leads still use UL rated wire. I was just surprised to see that the test leads were actually pretty decent. The banana plug uses a machined banana pin (not just a formed one). In general the leads feel very nice.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: January 02, 2013, 02:18:34 am
content: Being bored today and trying to recover from last night I decided to test some resistors and caps to see how it compares to the Uni-T 61E. First, the resistors:First set, 33kOhm metal film 0.1% 1/2W from KOASpeer (Electrohm brand) Model:SF:HF (UT61E)32.8 (32.87)32.8 (32.87)32.8 (32.87)32.8 (32.86)Average: 32.8k(32.87k)Error: -0.606%(-0.402%)Second set,33kOhm metal film 0.1% 1/2W from KOASpeer Model:RNS:32.8(32.89) 32.8(32.88)32.8(32.89) 32.8(32.89)32.8(32.89) 32.8(32.88)32.8(32.89)32.8(32.88)Average:32.8k(32.88625k)Error: -0.606%(-0.3447%)Third set, 33.2kOhm metal film 0.1% 1/3W from KOASpeer Model:MRS:33.0(33.07) 33.0(33.08)33.0(33.07) 33.0(33.08)33.0(33.08) 33.0(33.08)33.0(33.07) 33.0(33.08)33.0(33.08) 33.0(33.09)Average: 33.0k(33.078k)Error: -0.60241%(-0.36747%)Fourth set, 220kOhm metal film 0.1% 1/2W from KOASpeer (Electrohm brand) Model:SF:HF (UT61E)217(219.64) 217(219.63)217(219.65)217(219.63)217(219.61)217(219.62)Average: 217k(219.63)Error: -1.363%(-0.16818%)Fifth set, 220kOhm metal film 0.1% 1/2W from KOASpeer Model:RNS:217(219.67) 217(219.68) 217(219.68)217(219.67) 217(219.64) 217(219.68)217(219.70) 217(219.68)217(219.68) 217(219.67)217(219.69) 217(219.74)Average: 217k(219.6817)Error: -1.363%(-0.1447%)Sixth set, 2kOhm metal film 0.1% 1/2W from KOASpeer (Electrohm brand) Model:SF:1.995(1.9941) 1.995(1.9941)1.995(1.9938) 1.995(1.9942)1.995(1.9938) 1.995(1.9937)1.995(1.9940) 1.995(1.9939)1.995(1.9939) 1.995(1.9938)Average: 1.995k(1.99393k)Error: -0.25%(-0.3035%)Seventh set, 2kOhm metal film 0.1% 1/2W from KOASpeer Model:RNS:1.995(1.9945) 1.996(1.9955) 1.996(1.9956) 1.996(1.9954)1.996(1.9951) 1.996(1.9949) 1.995(1.9956) 1.996(1.9950)1.995(1.9946) 1.996(1.9952) 1.996(1.9949) 1.996(1.9952)1.996(1.9950) 1.996(1.9953) 1.995(1.9947) 1.996(1.9948)1.995(1.9944) 1.996(1.9951) 1.995(1.9942) 1.996(1.9953)Average: 1.9958k(1.99501k)Error: -0.21%(-0.24925%)Eighth set,2kOhm metal film 0.1% 1/3W from KOASpeer Model:MRS:1.989(1.9948) 1.989(1.9945)1.989(1.9944) 1.989(1.9948)1.989(1.9947) 1.989(1.9948)1.988(1.9946) 1.989(1.9947)1.989(1.9948) 1.989(1.9947)Average: 1.9889k(1.99468k)Error: -0.555%(-0.266%)It is clear that the 61E is more precise, though accuracy on some for the HF DMM is actually technically better than the 61E. On the flipside, when the HF DMM is bad it gets really bad, getting more than 1% off for the resistance.