Beckman Industrial HD140 Multimeter

Beckman Industrial HD140 MultimeterThe HD140 digital multimeter from Beckman Industrial is another in the “heavy-duty” series, very similar to the HD110 in a previous article.  Unlike the HD110 however, this is a 20,000-count 4½ digit model with RMS-responding AC capability.

Unfortunately I can find no information on it other than the fact it shares a service manual with the 4410 model.  Presumably the internals are the same, except that the HD140 has the extra-sturdy safety yellow enclosure.

This unit arrived with a small problem in the two least-significant digits.  Some segments were very dim or flickering.  This is the classic “faded segments” problem that often plagues older instruments with liquid-crystal displays. It is usually caused by contamination on the contact surfaces of the elastomeric connector (a.k.a. zebra strip) that couples the very low-current drive signals from the printed-circuit board (PCB) to the glass LCD.  This problem is often affected by mechanical pressure on the LCD.  In other words, you can squeeze it and make it look better or worse.

Fading segments should not be confused with more serious problems.  In some cases one or more segments will never come on at all, not even dimly.  This would indicate that the problem likely lies within the LCD glass itself, or with the semiconductor components driving the LCD.   If all the segments are uniformly faded or have low contrast over the entire display, then that symptom might indicate a sun-faded polarizer, or failing drive components.

Mere Alcohol Doesn’t Thrill Me At All

A quick cleaning of the PCB pads, connector strip, and the glass LCD contact surface with isopropyl alcohol (IPA) usually clears up the faded segment problem, just as it did here.  The simple cleaning procedure doesn’t warrant a lengthy explanation, so let’s just have a look at the restoration process from start to finish, and then take a good look at how it’s made.

 Missed It By THAT Much

I’m not very impressed with the extra digit of resolution in this unit.  It tends to “bobble” quite a bit, even for a very stable input.  It is normal for a DMM to flicker between two sequential values on occasion, but this one tends to make excursions both up and down by 1 count.  Not a huge problem, but it does not instill confidence in the device’s precision.  Without documentation, I can’t say for sure this unit meets its accuracy specifications.  The extra digit of resolution makes it hard to appear “spot-on”, but with an error of 0.06% at 5VDC, I would hazard a guess that it is in good shape.

Many DMM models have a simple calibration procedure that involves the use of a single low-voltage DC reference level (usually around 90% of full-scale) and a single trim potentiometer to adjust the unit’s basic DC measuring ability.  The accuracy of the rest of its functions will then simply depend on the tolerances of components like the precision resistors used in the voltage divider network.  Others have a more complicated set-up.  This particular model falls into the latter category.

The HD140 has 3 variable resistors and 3 variable capacitors.  None of them are labeled.  The trim caps are there to compensate the voltage divider network at AC frequencies higher than just 50 or 60Hz mains.  Proper adjustment requires the manufacturer’s recommended calibration procedure, and a means to generate the stable reference signals required.  Lacking both the procedure documentation and the necessary equipment, no effort was made to adjust this unit’s calibration.

DMMCheck calibration check results for this Beckman HD140:

Reference Reading Notes
DC 5V 4.997
1mA 1.0002
AC 5V 4.986
1mA 0.9954
Ohms 100Ω 0.1006K 0.0006K with leads shorted
1K 1.0004
10K 10.006
100K 100.06

Other Measurements

Current consumption was measured at 1.42 mA on both AC and DC function settings.  The low-battery annunciator comes on at a battery voltage of 7.15V.  Accurate measurements were still possible down to 5.00V.  Open-circuit voltage on the 2KΩ (diode-check) range was 3.88V, enough to illuminate and measure the Vf of a red LED.

About modemhead

Fixologist and multimeter junkie.
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9 Responses to Beckman Industrial HD140 Multimeter

  1. harvey says:

    Looks pretty dam accurate to me and it washed up a blooming treat 🙂

    Ive had cheap-n-cheerfull meters with a dodgy zebra strip, cleaning didnt work, i then resorted to applying thin strips of sticky parcel label to the inside of the plastic pushdown part.

    Just needs a tiny bit extra pressure to an old strip and works fine, yes its a bit bodgy but when all else fails you have to pack it a bit.

    That battery compartment was the most stupid i have ever seen, mad!!.

    Hmm plastic fantastic…..:-( ive put a cable/zip tie around split tubes and then applied hot glue to keep it in place, bodge bodge lol 🙂
    And for missing tubes a hacked up pen tube becomes a stand in.

    • modemhead says:

      It’s interesting that the exact same fantastic plastic bit failed in my other specimen from the HD series. It is a tough box, except for those screw posts.

      Parcel labels and pen tubes. A must for any repairer’s toolbox. Zip ties and hot glue though, too easy, that’s for amateurs. 🙂

  2. Joe says:

    I have a Beckman HD 140 that has developed a fault in reading AC voltage. AC 200 scale is normal for my routine tests of wall outlet voltage. The multimeter still tests resistance just fine, so the leads are still serviceable. The unit was opened and found an oxidized fuse in use. Cleaned fuse, holder and saw no change. Fuse has continuity. General cleaning was done while the case was open, but to no avail on the AC voltage measuring issue. Could a chip be at fault?
    Does Beckman do diagnosis over the phone, or do I need to send the multimeter to Beckman or another reputable repair facility? Thanks!

    • modemhead says:

      Beckman is no longer a company. It was absorbed into Wavetek, which then apparently disappeared into a Meterman/Amprobe jungle. Professional repair cost would be several times the price of a new DMM. If it isn’t something simple like dirty switch contacts, it could be a fault in the AC converter circuit, possibly an op-amp or one of those tantulum caps. Sorry I don’t have a schematic for this model so I can’t be very specific.

      • Joe says:

        Thanks! I appreciate your wisdom! I will look into a new meter.
        Joe
        PS Did I remember you saying the schematic for the HD140 was like the HD110? Mine is not the Industrial Model I guess because it only has Beckman HD140 printed below the display.

      • modemhead says:

        Somewhere along the line, “Beckman” became “Beckman Industrial”, so I think the presence of the word “Industrial” on the front relates to manufacturing date more than anything else.

        The HD140 is a 4-1/2 digit design based on the Intersil 7129. The 110, and other similar models, are 3-1/2 digit designs based on the Beckman 270-100 chip. So the schematics are probably quite different.

  3. Bob Kovach says:

    I have a Beckman CT-233 with all the trimmings leather case and includes the CT clamp on and a host of Probes. Also in the leather case is the HD140. I am looking to
    get it repaired. The HD140 does not come on when you turn it on. When I first got it
    the case wood get warm to the touch and that was it. One of the sites had an estimated repair cost based on repair of other units at $184.oo Does anyone know a respectable repair shop that can repair the HD140? at a reasonable cost? Free evaluation? I get
    leary about Free anything. There isn’t “no free lunch”

  4. George Gill says:

    I have a Beckman Industrial HD130B I can’t get the battery out. I have removed all screws ? and I can’t raise circuit board to get to the battery? It says to release battery remove 15A fuse? Any suggestions? Thanks

    • modemhead says:

      Not familiar with that model, but it’s probably like this HD110 I have where the large HRC fuse obstructs the battery compartment. In which case, remove the two short self-tapping screws at the bottom of the circuit board near the input jacks. Then remove the two long diagonally-opposed self-tapping screws that go through the rotary switch assembly. Don’t worry, the switch assembly will stay together because there are two more screws on the front side holding it together. Pull the board assembly straight up, which will give access to the battery. The switch shaft disengages without having to do anything special, just line it back up during re-assembly.

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