Sperry Dm 4400a Digital Multimeter Continuously Beeps

Hello all,
I recently got a couple new multimeters to try out for my lab at home, and seeing as I couldn't find any teardowns of them anywhere online, I thought I would post some internal photos here. I have already done a teardown of the Sperry Instruments DM-8200. You can find it here:
https://www.eevblog.com/forum/testgear/teardown-and-impressions-of-sperry-instruments-dm-8200-techmaster-multimeter/

This next meter is another Sperry called the DM-4400A, a 2000-count, Cat. II rated, autoranging multimeter that I picked up new on Ebay for around USD $20.

As with my previous teardown, the best meter currently in my possession is my old Fluke 23 III, so I will use that as my "gold standard" for comparisons, although I will also be comparing it to the DM-8200 considering that both are from the same manufacturer and can both be purchased on Ebay for about the same prices at the time of posting.

This meter has some issues with its design and some very severe safety issues. Overall, in spite of a few good features, the unit is just poorly designed, and an absolute deathtrap in terms of safety due to massively improper overload protection. You can skip to the bottom for my pros/cons list, but here are my full, lengthy notes on it:

Unboxing and First Impressions:

The unit arrived in one of those absolutely evil plastic clamshell packages, which contained the probes, a manual booklet, a "Golden Power" battery (everyone's favorite), and the meter itself, of course. The main feature which drew me to buy this meter was the big rubber surround on the case. In a lot of ways, it is very reminiscent of the older Fluke series II and III meters (only with the colors inverted). Seeing it in person, the rubber surround seems to be of reasonable quality and is not too difficult to take on and off-- it even has the molded ribs on the inside to give it added drop protection. I'm reasonably confident that this would provide good survivability if I were to drop this meter. Even with the rubber surround on, the unit is fairly compact, measuring in at roughly 5.75x3.25 inches and 2 inches deep (14.6x8.3x5.1 cm). With the rubber surround removed, the unit measures 5.25x3x1.75 inches (13.3x7.6x4.4 cm, including the top of the range switch in the depth measurement).

After wrestling the unit out of the packaging (and disposing of the Golden Power battery), I noticed the first issue with this meter: the probes do not have proper shrouding on bananna plug inputs. The probes generally feel plastic-y and cheap, and have noticeable imperfections in the molding from the injection gates (you can't really see them in this image). Not a good start.

The manual booklet is fairly thick and includes the full manual in three languages (English, Spanish, and French). The paper quality does not seem to be quite as good as the manual for the DM-8200, but the printing and overall quality is still quite good, with well-labeled images, calibration procedures, and even what appears to be complete parts listing and a partial circuit diagram, which seems very generous of them. The front of the manual is marked with a cryptic "04/06" in the corner, which I presume means it was written or last revised in April 2006.

First use:

Although the LCD in this unit is on the small side, the digits themselves are quite large and make good use of the limited space. With no bar graph at the bottom taking up screen space, the digits are almost as large as on my Fluke. In spite of having a plastic shield on the face of the meter, the LCD inside is not very well protected, and pressing on the face of the meter causes the segments to appear.

Another bizarre feature on the display is that when the unit is over-range, instead of displaying the typical "OL" or blanking out all the numbers except the 4th digit (this is often done on many 2000-count meters), the unit displays "1000" but then flashes the "1" on and off. I suppose I could get used to a meter that did that, but it really confused me when I first saw it. The image below shows the meter just as the 1 is fading out.

The meter has all the basic functions, including mA and microamps ranges for both DC and AC. The microamps range only has a minimum resolution of 1uA, as opposed to the DM-8200 which goes down  to 0.1uA resolution. The ranging speed is quite slow-- in the Ohms setting it took maybe about 3 seconds for it to range from an open circuit down to 0 Ohms. Not good at all. The unit also has a non-contact voltage detection function, which isn't really something I would use that much, but I guess could be considered a useful feature. The range switch also has "off" settings on either end of its rotation, which is a nice touch. EDIT: the unit also doesn't appear to have an auto turn-off at all.

The continuity tester is latched, but has a slight delay on it of about a quarter of a second. The cheap probes are finicky about making constant contact, so it is difficult to estimate it accurately.  The beeper is surprisingly loud even with the rubber surround on it, perhaps even a bit too loud.

One really irritating feature of this meter is that the unit makes a loud beep and flashes the LED for the NCV every time you change the range, and switching across multiple ranges causes it to beep for each click on the range switch-- no matter how quickly you turn it-- so changing to a function multiple clicks away from the one you are on will result in a string of loud beeps that will be sure to annoy anyone in the vicinity. My Fluke also makes a beep whenever you change the range, but it is a much quieter and more subtle beep that isn't nearly as bothersome.

The range switch is slightly on the stiff side, but generally pretty decent. It snaps cleanly from one position to the next with no sponginess or risk of getting stuck between positions (more on that when I take it apart. The internal construction is similar to the DM-8200). Thanks to the rubber surround, the unit does not slide at all when turning the range switch when the meter is laid flat, but trying to turn it with the surround taken off causes it to slide quite a bit. The folding stand, although reasonably wide and stable against rocking or falling over, does not provide good friction, and causes the unit to slide and pivot around if you try and turn the range switch without applying downward pressure.

On the back of the Unit, I noticed that the unit had a UL listing file number on the label for the unit (E178257), however, entering the file number into UL's database did not return anything. Now, just because a random guy like me couldn't find it after a few minutes on google doesn't mean it isn't listed, so I'm not about to make any accusations. That said, between the unshrouded probes and the lack of proper fusing inside (we'll get to that in a moment), I would kind of like to see some confirmation of this product's category II and UL listed status.

The accuracy ratings are not that amazing: 0.5%+4d on the volts range, etc. It generally seemed to be within its rated accuracy when measured against my Fluke, but unfortunately my Fluke hasn't been calibrated in YEARS,  so I cannot really confirm the accuracy of these ratings.

Taking it Apart

The unit has a removable cover for the 9V battery compartment, which is just held in by some pressure-fit clips in the casing rather than a screw. Having a separate compartment is definitely appreciated, but I feel like the plastic clips might wear out after too much use. The entire case is held together by one self-tapping screw and some clips up at the top of the casing.

Inside, I immediately noticed that the unit has a standard 250V glass fuse for the mA range, and no fuse at all for the 10A range. Now, I wouldn't consider Sperry Instruments to be a top tier brand for multimeters by any means, but for a company that claims to be a manufacturer of professional tools, that's just unacceptable. Even if everything else on this meter were perfect (and it's not), the lack of proper fusing in this meter renders it basically unusable to me.

Everything else after that is pretty standard. The board has a single PTC covered in shrink tubing, and the overall layout is pretty minimal and not overly crowded. The 10A shunt has shrink tubing over it, presumably to provide better isolation from the fuse clip for the mA range and the input posts right next to it. The main front end of the unit is a JRC NJU9207F chip. The input jacks are the standard solid tube type, riveted down to metal strips over the input posts in the case.

Bizarrely, there seems to be a red LED marked as D1 on the inside of the case (on the top right in the image below). The LED for the NCV detection is on the other side of this board, and this LED wouldn't even be visible from outside the case, so I have absolutely no idea what it is for. After a minute or two of messing around with various functions on the meter, I couldn't get it to light up, so I can only presume that it is for some kind of debugging function.

Unscrewing the board and turning it over to the other side revealed surprisingly good quality gold plating on the traces for the range switch-- actually, both sides of this board have gold plating on the pads and plated-through vias, so I do believe that this is a properly ENIG-plated board. The buttons appear to be fairly standard rubber ones. They were stuck to the board, so I decided to leave them untouched for fear that I might not be able to put them back on again. The LCD is just connected on with a zebra-strip and held together by the pressure of the closed casing.

The range switch is a similar ball-bearing construction to the DM-8200; the position of the switch is held in place by two tiny ball bearings suspended on springs, which are pressed into a wavy track on the front panel of the case, which allows the switch to provide tension as the ball bearing rolls up one of the ridges, then snap across down to the next position as the ball bearing crests over the top of the ridge.

tl;dr here are my pros and cons on this meter:

Pros:
-reasonably thick rubber surround with molded ribs on the inside
-rubber surround prevents meter from sliding when laid flat
-good quality range switch with ball bearings and gold-plated traces
-gold-plated PCB
-reasonable quality manual with calibration procedures and circuit diagram
-separate battery compartment
-non-contact voltage sensor function

Cons:
-NO FUSE FOR 10A RANGE
-standard 250V glass fuse for mA range
-cheap, improperly shrouded probes
-a single PTC for input protection
-folding stand does not provide enough friction to keep the meter from sliding
-LCD is not well protected; pressing on the face of the meter causes segments to appear
-microamps range does not have 0.1uA resolution.
-unit makes a loud beep and flashes the LED whenever the range is changed
-case is held together with a single screw, and the battery compartment is held on only by plastic clips
-possible questions with UL listed and Cat. II status
-EDIT: the unit also doesn't appear to have an auto turn-off at all.

Overall, I don't think I will be using this meter. Nice features like rubber surrounds and gold-plated PCBs are rendered all but meaningless if the meter doesn't even have fuses on all the ranges. Even in this price range, this is the level of design quality I would expect of a no-name Chinese knockoff, not a brand-name meter from a seller of electricians tools. Many brand-name DMM manufacturers still manage to have proper fuse protection in even their cheapest of meters, so a meter without fusing on all the inputs is an immediate deal-breaker for me. Looking back at the page where I bought it, I should have spotted the marking on the front for the unfused 10A range, but I'm still just baffled that Sperry deemed this acceptable to put their brand name on.

My last question for everyone is going back to that UL listing and Cat. II rating: is it really possible for an unfused meter to be Cat. II rated? what are the requirements for this?

This is only my second time posting here, so let me know if this was a good teardown of this multimeter, or let me know any other things I should add, correct, or take out for future first impressions. I still have a couple more meters to look at, so more tear down threads will likely follow if people want them. I'm mainly just doing this so that the information can be out there for people who want to see the inside of this particular multimeter.

Cheers,
JLNY

lockwooddiscus.blogspot.com

Source: https://www.eevblog.com/forum/testgear/teardown-and-impressions-of-sperry-instruments-dm-4400a-multimeter/

Share this post